ORCID Profile
0000-0002-8478-533X
Current Organisation
Monash University
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Atmospheric Sciences | Cloud Physics | Atmospheric Dynamics | Climatology (excl. Climate Change Processes) | Meteorology | Physical Geography and Environmental Geoscience | Atmospheric Aerosols | Meteorology | Climate Change Processes | Surface Processes | Water Resources Engineering | Atmospheric sciences | Environmental Management And Rehabilitation | Climatology (Incl. Palaeoclimatology) | Global Change Biology | Other Chemical Sciences | Cloud physics | Climate change processes | Other Biological Sciences | Atmospheric dynamics | Environmental Chemistry (incl. Atmospheric Chemistry) | Environmental Management | Physical Geography
ANZSRC Socio-Economic Objective (SEO)
Weather | Atmospheric Processes and Dynamics | Weather | Climate Variability (excl. Social Impacts) | Atmospheric processes | Mountain and High Country Land and Water Management | Effects of Climate Change and Variability on Antarctic and Sub-Antarctic Environments (excl. Social Impacts) | Effects of Climate Change and Variability on Australia (excl. Social Impacts) | Ecosystem Assessment and Management of Antarctic and Sub-Antarctic Environments | Atmospheric Composition (incl. Greenhouse Gas Inventory) | Antarctic and Sub-Antarctic Air Quality | Hydro-electric | Natural Hazards in Urban and Industrial Environments | Land and water management | Climate variability | Climate change | Natural Hazards in Fresh, Ground and Surface Water Environments | Hydro-Electric Energy | Environmental Policy, Legislation and Standards not elsewhere classified |
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Publications
On the Analysis of a Cloud Seeding Dataset over Tasmania
Publisher: American Meteorological Society
Date: 06-2009
Abstract: An analysis of cloud seeding activity for the period 1960–2005 over a hydroelectric catchment (target) area located in central Tasmania, Australia, is presented. The analysis is performed using a double ratio on monthly area-averaged rainfall for the months of May–October. Results indicate that increases in monthly precipitation are observed within the target area relative to nearby controls during periods of cloud seeding activity. Ten independent tests were performed and all double ratios found are above unity with values that range from 5% to 14%. Nine out of 10 confidence intervals are entirely above unity and overlap in the range of 6%–11%. Nine tests obtain levels of significance & .05 level. If the Bonferroni adjustment is made to account for multiple comparisons, six tests are found to be significant at the adjusted alpha level. Further field measurements of the cloud microphysics over this region are needed to provide a physical basis for these statistical results.
Simulation of Heavy Precipitation and the Production of Graupel Related to the Passage of a Cold Front over the Australian Snowy Mountains
Publisher: American Meteorological Society
Date: 12-2022
Abstract: The case study of a heavy precipitation event associated with the passage of cold front over the Australian Snowy Mountains (ASM) on 3 August 2018 has been examined using the observational data from an intensive field c aign and high-resolution (1 km) Weather Research and Forecasting (WRF) simulation. We ided this event into prefrontal, cold front, and postfrontal periods. The cold front and postfrontal periods were characterized by higher production of graupel, while relatively low graupel was produced in the prefrontal period. Overall, aggregation along with deposition are likely the main growth mechanisms of snow in the prefrontal clouds, while heavy rain was produced below the melting level over windward slopes of the ASM. The simulated melting level is lower compared to the observations, which is consistent with model cold bias. Stronger orographic uplift and frontal forcing were mainly responsible for the enhanced supercooled liquid water (SLW) production over the ASM in the cold front period. A drop in elevation of the freezing level and increase in low-level relative humidity further enhanced the SLW production. The production of graupel through riming processes was highly efficient in the cold front period given the high concentration of ice-phase hydrometeors in the frontal clouds and the development of clouds comprising supercooled liquid water. The orographic updrafts and embedded convection were the main dynamical processes generating postfrontal SLW clouds and graupel. Ice initiation processes were activated once SLW cloud tops reached −15°C level followed by graupel production through riming processes.
Fungal Planet description sheets: 1383–1435
Publisher: Naturalis Biodiversity Center
Date: 30-06-2022
DOI: 10.3767/PERSOONIA.2022.48.08
Abstract: Novel species of fungi described in this study include those from various countries as follows: Australia , Agaricus albofoetidus , Agaricus aureoelephanti and Agaricus parviumbrus on soil, Fusarium ramsdenii from stem cankers of Araucaria cunninghamii , Keissleriella sporoboli from stem of Sporobolus natalensis , Leptosphaerulina queenslandica and Pestalotiopsis chiaroscuro from leaves of Sporobolus natalensis , Serendipita petricolae as endophyte from roots of Eriochilus petricola , Stagonospora tauntonensis from stem of Sporobolus natalensis , Teratosphaeria carnegiei from leaves of Eucalyptus grandis × E. camaldulensis and Wongia ficherai from roots of Eragrostis curvula . Canada , Lulworthia fundyensis from intertidal wood and Newbrunswickomyces abietophilus (incl. Newbrunswickomyces gen. nov.)on buds of Abies balsamea . Czech Republic , Geosmithia funiculosa from a bark beetle gallery on Ulmus minor and Neoherpotrichiella juglandicola (incl. Neoherpotrichiella gen. nov.)from wood of Juglans regia . France , Aspergillus rouenensis and Neoacrodontium gallica (incl. Neoacrodontium gen. nov.)from bore dust of Xestobium rufovillosum feeding on Quercus wood, Endoradiciella communis (incl. Endoradiciella gen. nov.)endophyticin roots of Microthlaspi perfoliatum and Entoloma simulans on soil. India , Amanita konajensis on soil and Keithomyces indicus from soil. Israel , Microascus rothbergiorum from Stylophora pistillata . Italy , Calonarius ligusticus on soil. Netherlands , Appendopyricularia juncicola (incl. Appendopyricularia gen. nov.), Eriospora juncicola and Tetraploa juncicola on dead culms of Juncus effusus , Gonatophragmium physciae on Physcia caesia and Paracosmospora physciae (incl. Paracosmospora gen. nov.)on Physcia tenella , Myrmecridium phragmitigenum on dead culm of Phragmites australis , Neochalara lolae on stems of Pteridium aquilinum , Niesslia nieuwwulvenica on dead culm of undetermined Poaceae , Nothodevriesia narthecii (incl. Nothodevriesia gen. nov.) on dead leaves of Narthecium ossifragum and Parastenospora pini (incl. Parastenospora gen. nov.)on dead twigs of Pinus sylvestris . Norway , Verticillium bjoernoeyanum from sand grains attached to a piece of driftwood on a sandy beach. Portugal , Collybiopsis cimrmanii on the base of living Quercus ilex and amongst dead leaves of Laurus and herbs. South Africa , Paraproliferophorum hyphaenes (incl. Paraproliferophorum gen. nov.) on living leaves of Hyphaene sp. and Saccothecium widdringtoniae on twigs of Widdringtonia wallichii . Spain , Cortinarius dryosalor on soil, Cyphellophora endoradicis endophytic in roots of Microthlaspi perfoliatum , Geoglossum laurisilvae on soil, Leptographium gemmatum from fluvial sediments, Physalacria auricularioides from a dead twig of Castanea sativa , Terfezia bertae and Tuber davidlopezii in soil. Sweden , Alpova larskersii , Inocybe alpestris and Inocybe boreogodeyi on soil. Thailand , Russula banwatchanensis , Russula purpureoviridis and Russula lilacina on soil. Ukraine , Nectriella adonidis on over wintered stems of Adonis vernalis . USA , Microcyclus jacquiniae from living leaves of Jacquinia keyensis and Penicillium neoherquei from a minute mushroom sporocarp. Morphological and culture characteristics are supported by DNA barcodes.
Wintertime In Situ Cloud Microphysical Properties of Mixed‐Phase Clouds Over the Southern Ocean
Publisher: American Geophysical Union (AGU)
Date: 27-05-2021
DOI: 10.1029/2021JD034832
Abstract: In situ observations made over 20 flights during three Austral winters (June to October 2013–2015) were analyzed to characterize the cloud microphysical properties and natural variability of mid‐latitude shallow convective clouds over the Southern Ocean (SO), with a focus on pristine conditions and the mixed‐phase temperature range (MPTR, 0°C to −31°C). Liquid, mixed‐phase, and ice cloud fractions were observed 39%, 44%, and 17% of the time, respectively, under various meteorological settings. Liquid phase clouds were typically characterized by low droplet number concentrations and the common presence of drizzle. Supercooled liquid water was prevalent in the MPTR, while freezing of supercooled raindrops likely formed the primary ice nucleation mechanism in these shallow clouds. Ice particles of various habits were present in the mature/maturing convective cloud cells, suggesting the operation of multiple particle growth regimes. Increased ice particle concentrations (exceeding 100 L −1 ), well in excess of the expected ice nuclei concentrations, were measured at temperature warmer than approximately −12°C, signaling the operation of secondary ice production mechanisms. However, these cloud segments were spatiotemporally inhomogeneous, suggesting the chaotic and turbulent nature of the secondary ice‐forming processes. Accurately representing these processes in global models, while necessary, is likely a challenge. Our analysis also found marked inconsistencies between several satellite‐based cloud phase products that have underpinned recent developments of model parameterization frameworks. Understanding and addressing these inconsistencies are critical toward improving the representation of SO clouds and their radiative properties in climate models.
Experimental, Observational, and Numerical Research on Intentional and Inadvertent Weather Modification
Publisher: Hindawi Limited
Date: 28-06-2018
DOI: 10.1155/2018/1613756
Observations of high droplet number concentrations in Southern Ocean boundary layer clouds
Publisher: Copernicus GmbH
Date: 27-01-2016
Abstract: Abstract. Cloud physics data collected during the NSF/NCAR High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) Pole-to-Pole Observations (HIPPO) c aigns provide a snapshot of unusual wintertime microphysical conditions in the boundary layer over the Southern Ocean. On 29 June 2011, the HIAPER s led the boundary layer in a region of pre-frontal warm air advection between 58 and 48° S to the south of Tasmania. Cloud droplet number concentrations were consistent with climatological values in the northernmost profiles but were exceptionally high for wintertime in the Southern Ocean at 100–200 cm−3 in the southernmost profiles. Sub-micron (0.06 D 1 µm) aerosol concentrations for the southern profiles were up to 400 cm−3. Analysis of back trajectories and atmospheric chemistry observations revealed that while conditions in the troposphere were more typical of a clean remote ocean airmass, there was some evidence of continental or anthropogenic influence. However, the hypothesis of long-range transport of continental aerosol fails to explain the magnitude of the aerosol and cloud droplet concentration in the boundary layer. Instead, the gale force surface winds in this case (wind speed at 167 m above sea level was 25 m s−1) were most likely responsible for production of sea spray aerosol which influenced the microphysical properties of the boundary layer clouds. The smaller size and higher number concentration of cloud droplets is inferred to increase the albedo of these clouds, and these conditions occur regularly, and are expected to increase in frequency, over windy parts of the Southern Ocean.
Understanding Orographic Effects on Surface Observations at Macquarie Island
Publisher: American Meteorological Society
Date: 11-2016
Abstract: The meteorological observations on Macquarie Island have become of increasing value for efforts to understand the unique nature of atmospheric processes over the Southern Ocean. While the island is of modest elevation (peak altitude of 410 m), the orographic effects on observations on this island are still not clear. High-resolution numerical simulations [Weather Research and Forecasting (WRF) Model] with and without terrain have been used to identify orographic effects for four cases representing common synoptic patterns at Macquarie Island: a cold front, a warm front, postfrontal drizzle, and a midlatitude cyclone. Although the simulations cannot capture every possible feature of the precipitation, preliminary results show that clouds and precipitation can readily be perturbed by the island with the main enhancement of precipitation normally in the lee in accordance with the nondimensional mountain height being much less than 1. The weather station is located at the far north end of the island and is only in the lee to southerly and southwesterly winds, which are normally associated with drizzle. The station is on the upwind side for strong northwesterly winds, which are most common and can bring heavier frontal precipitation. Overall the orographic effect on the precipitation record is not found to be significant, except for the enhancement of drizzle found in southwesterly winds. Given the strong winds over the Southern Ocean and the shallow height of the island, the 3D nondimensional mountain height is smaller than 1 in 93.5% of the soundings. As a result, boundary layer flow commonly passes over the island, with the greatest impact in the lee.
In-situ observations of wintertime low-altitude clouds over the Southern Ocean
Publisher: Wiley
Date: 04-2017
DOI: 10.1002/QJ.3011
Radar‐based climatology of damaging hailstorms in Brisbane and Sydney, Australia
Publisher: Wiley
Date: 2020
DOI: 10.1002/QJ.3693
Quantification of volcanic cloud top heights and thicknesses using A-train observations for the 2008 Chaitén eruption
Publisher: American Geophysical Union (AGU)
Date: 13-04-2015
DOI: 10.1002/2014JD022399
Corrigendum to "An evaluation of COSMIC radio occultation data in the lower atmosphere over the Southern Ocean" published in Atmos. Meas. Tech., 8, 97–107, 2015
Publisher: Copernicus GmbH
Date: 22-01-2015
A Numerical Study of the Interaction between Stratocumulus and the Air Overlying It
Publisher: American Meteorological Society
Date: 11-1993
Airborne observations of the effect of a cold front on the aerosol particle size distribution and new particle formation
Publisher: Wiley
Date: 04-2010
DOI: 10.1002/QJ.515
A climatology of open and closed mesoscale cellular convection over the Southern Ocean derived from Himawari-8 observations
Publisher: Copernicus GmbH
Date: 15-02-2022
Abstract: Abstract. Marine atmospheric boundary layer clouds cover vast areas of the Southern Ocean (SO), where they are commonly organized into mesoscale cellular convection (MCC). Using 3 years of Himawari-8 geostationary satellite observations, open and closed MCC structures are identified using a hybrid convolutional neural network. The results of the climatology show that open MCC clouds are roughly uniformly distributed over the SO storm track across midlatitudes, while closed MCC clouds are most predominant in the southeast Indian Ocean, with a second maximum along the storm track. The ocean polar front, derived from ECMWF-ERA5 sea surface temperature gradients, is found to be aligned with the southern boundaries for both MCC types. Along the storm track, both closed and open MCCs are commonly located in post-frontal, cold air masses. The hourly classification of closed MCC reveals a pronounced daily cycle, with a peak occurring late night/early morning. Seasonally, the diurnal cycle of closed MCC is most intense during the summer months (December–February DJF). Conversely, almost no diurnal cycle is evident for open MCC.
An evaluation of COSMIC radio occultation data in the lower atmosphere over the Southern Ocean
Publisher: Copernicus GmbH
Date: 09-01-2015
Abstract: Abstract. The global positioning system (GPS) radio occultation (RO) method is a relatively new technique for taking atmospheric measurements for use in both weather and climate studies. As such, this technique needs to be evaluated for all parts of the globe. Here, we present an extensive evaluation of the performance of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) GPS RO observations of the Southern Ocean boundary layer. The two COSMIC products used here are the "wetPrf" product, which is based on 1-D variational analysis with European Centre for Medium-Range Weather Forecasts (ECMWF), and the "atmPrf" product, which contains the raw measurements from COSMIC. A direct comparison of temporally and spatially co-located COSMIC profiles and high resolution radiosonde profiles from Macquarie Island (54.62° S, 158.85° E) highlights weaknesses in the ability of both COSMIC products to identify the boundary layer structure, as identified by break points in the refractivity profile. In terms of reproducing the temperature and moisture profile in the lowest 2.5 km, the "wetPrf" COSMIC product does not perform as well as an analysis product from the ECMWF. A further statistical analysis is performed on a large number of COSMIC profiles in a region surrounding Macquarie Island. This indicates that, statistically, COSMIC performs well at capturing the heights of main and secondary break points. However, the frequency of break points detected is lower than the radiosonde profiles suggest, but this could be simply due to the long horizontal averaging in the COSMIC measurements. There is also a weak seasonal cycle in the boundary layer height similar to that observed in the radiosonde data, providing some confidence in the ability of COSMIC to detect an important boundary layer variable.
Terrestrial sources and sinks of halomethanes near Cape Grim, Tasmania
Publisher: Elsevier BV
Date: 07-2004
Impact of variations in upper-level shear on simulated supercells
Publisher: American Meteorological Society
Date: 07-2017
Abstract: It has previously been suggested, based on limited observations, that vertical wind shear in the upper troposphere is a key control on supercell morphology, with the low-precipitation, high-precipitation, and classic archetypes favored under strong, weak, and moderate shear, respectively. The idea is that, with increasing upper-level shear (ULS), hydrometeors are transported farther from the updraft by stronger storm-relative anvil-level winds, limiting their growth and thereby reducing precipitation intensity. The present study represents the first attempt to test this hypothesis, using idealized simulations of supercells performed across a range of 6–12-km shear profiles. Contrary to expectations, there is a significant increase in surface precipitation and an associated strengthening of outflow winds as ULS magnitude is increased from 0 to 20 m s −1 . These changes result from an increase in storm motion, which drives stronger low-level inflow, a wider updraft, and enhanced condensation. A further increase in ULS magnitude to 30 m s −1 promotes a slight reduction in storm intensity associated with surging rear-flank outflow. However, this transition in behavior is found to be sensitive to other factors that influence cold-pool strength, such as mixed-layer depth and model microphysics. Variations in the vertical distribution and direction of ULS are also considered, but are found to have a much smaller impact on storm intensity than variations in ULS magnitude. Suggestions for the disparity between the current results and the aforementioned observations are offered and the need for further research on supercell morphology—in particular, simulations in drier environments—is emphasized.
Regional Variation in the Wet Season of Northern Australia
Publisher: American Meteorological Society
Date: 12-2016
Abstract: Variability in the wet season of tropical northern Australia is examined over its main months, November–March, with a focus on zonal differences between the western, central, and eastern domains, which encompass the northern parts of Western Australia, Northern Territory, and Queensland, respectively. The seasonal progression of the wet season is similar across the region, with steadily increasing atmospheric moisture and rainfall into the core months of the monsoon, January and February, decreasing into March. This seasonal progression differs in the eastern domain, where there is an extension of premonsoonal conditions into December, and a delay of the onset of the monsoon until January. An analysis of TRMM precipitation features (PFs) reveals more intense convection during the premonsoon, steadily decreasing in intensity to much shallower convection by March, with a steady increase in the overall number of PFs throughout the wet season. Regionally, the intensity of PFs steadily decreases eastward across northern Australia with significantly weaker, shallower PFs over the eastern domain. Intraseasonal variability associated with the Madden–Julian oscillation (MJO) has a consistent impact on the rainfall and the total number of TRMM PFs across northern Australia, with both increasing and decreasing during the active and suppressed phases, respectively. However, regional variations in the effect of the MJO lead to radically different characteristics of PFs during the suppressed phases intense convection and thunderstorms become more frequent over the western and central domains, while shallow PFs associated with the warm rain precipitation process increase in number over the eastern domain.
Calibrating Ground-Based Radars against TRMM and GPM
Publisher: American Meteorological Society
Date: 02-2018
DOI: 10.1175/JTECH-D-17-0128.1
Abstract: Calibration error represents a significant source of uncertainty in quantitative applications of ground-based radar (GR) reflectivity data. Correcting it requires knowledge of the true reflectivity at well-defined locations and times during a volume scan. Previous work has demonstrated that observations from certain spaceborne radar (SR) platforms may be suitable for this purpose. Specifically, the Ku-band precipitation radars on board the Tropical Rainfall Measuring Mission (TRMM) satellite and its successor, the Global Precipitation Measurement (GPM) mission Core Observatory satellite together provide nearly two decades of well-calibrated reflectivity measurements over low-latitude regions (±35°). However, when comparing SR and GR reflectivities, great care must be taken to account for differences in instrument sensitivity and frequency, and to ensure that the observations are spatially and temporally coincident. Here, a volume-matching method, developed as part of the ground validation network for GPM, is adapted and used to quantify historical calibration errors for three S-band radars in the vicinity of Sydney, Australia. Volume-matched GR–SR s le pairs are identified over a 7-yr period and carefully filtered to isolate reflectivity differences associated with GR calibration error. These are then used in combination with radar engineering work records to derive a piecewise-constant time series of calibration error for each site. The efficacy of this approach is verified through comparisons between GR reflectivities in regions of overlapping coverage, with improved agreement when the estimated errors are removed.
Assessing Surface Heat Flux Products with In Situ Observations over the Australian Sector of the Southern Ocean
Publisher: American Meteorological Society
Date: 09-2019
DOI: 10.1175/JTECH-D-19-0009.1
Abstract: Given the large uncertainties in surface heat fluxes over the Southern Ocean, an assessment of fluxes obtained by European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) product, the Australian Integrated Marine Observing System (IMOS) routine observations, and the Objectively Analyzed Air–Sea Heat Fluxes (OAFlux) project hybrid dataset is performed. The surface fluxes are calculated using the COARE 3.5 bulk algorithm with in situ data obtained from the NOAA Physical Sciences Division flux system during the Clouds, Aerosols, Precipitation, Radiation, and Atmospheric Composition over the Southern Ocean (CAPRICORN) experiment on board the R/V Investigator during a voyage (March–April 2016) in the Australian sector of the Southern Ocean (43°–53°S). ERA-Interim and OAFlux data are further compared with the Southern Ocean Flux Station (SOFS) air–sea flux moored surface float deployed for a year (March 2015–April 2016) at ~46.7°S, 142°E. The results indicate that ERA-Interim (3 hourly at 0.25°) and OAFlux (daily at 1°) estimate sensible heat flux H s accurately to within ±5 W m −2 and latent heat flux H l to within ±10 W m −2 . ERA-Interim gives a positive bias in H s at low latitudes ( °S) and in H l at high latitudes ( °S), and OAFlux displays consistently positive bias in H l at all latitudes. No systematic bias with respect to wind or rain conditions was observed. Although some differences in the bulk flux algorithms are noted, these biases can be largely attributed to the uncertainties in the observations used to derive the flux products.
Objective classification of precipitating convective regimes using a weather radar in Darwin, Australia
Publisher: No publisher found
Date: 2009
On the Decline of Wintertime Precipitation in the Snowy Mountains of Southeastern Australia
Publisher: American Meteorological Society
Date: 12-2011
Abstract: Data from a precipitation gauge network in the Snowy Mountains of southeastern Australia have been analyzed to produce a new climatology of wintertime precipitation and airmass history for the region in the period 1990–2009. Precipitation amounts on the western slopes and in the high elevations (& m) of the Snowy Mountains region have experienced a decline in precipitation in excess of the general decline in southeastern Australia. The contrast in the decline east and west of the ranges suggests that factors influencing orographic precipitation are of particular importance. A synoptic decomposition of precipitation events has been performed, which demonstrates that about 57% of the wintertime precipitation may be attributed to storms associated with “cutoff lows” (equatorward of 45°S). A further 40% was found to be due to “embedded lows,” with the remainder due to Australian east coast lows and several other sporadically occurring events. The declining trend in wintertime precipitation over the past two decades is most clearly seen in the intensity of precipitation due to cutoff lows and coincides with a decline in the number of systems associated with a cold frontal passage. Airmass history during precipitation events was represented by back trajectories calculated from ECMWF Interim Reanalysis data, and statistics of air parcel position were related to observations of precipitation intensity. This approach gives insight into sources of moisture during wintertime storms, identifying “moisture corridors,” which are typically important for transport of water vapor from remote sources to the Snowy Mountains region. The prevalence of these moisture corridors is associated with the southern annular mode, which corresponds to fluctuations in the strength of the westerly winds in southeastern Australia.
A historical monthly upper-air humidity dataset for Australia
Publisher: CSIRO Publishing
Date: 21-06-2023
DOI: 10.1071/ES22022
Abstract: Monthly humidity (represented as dew point temperature, DWPT) data from 22 land and 5 island Australian upper-air sites were analysed, with trends estimated over the 1965–2017 period at four pressure levels. Humidity data were selected to ensure that data collected under consistent s ling conditions were used (‘modified data’). The quality control process involved examining station metadata and applying an objective statistical test that detected discontinuities in the data series. At each station and pressure level, modified data series were adjusted (homogenised) on a monthly timescale when discontinuities were identified. Analysis of the homogenised (adjusted) modified DWPT data indicates that, over the 1965–2017 period, linear trends are mostly positive and smaller compared to unadjusted modified data. The all-Australian time-series show positive trends at the 850–400-hPa levels. The total increases in DWPT since 1965 at 850-, 700-, 500- and 400-hPa levels are ~0.5, ~1.2, ~1.3 and ~0.8°C respectively. The increase in humidity in the lower and middle troposphere is in accordance with the expectation that, as the troposphere warms, the amount of moisture in it should increase (at a differential rate of ~7% °C–1 at low altitudes globally, following Clausius–Clapeyron scaling) due to increasing surface evaporation and moisture-holding capacity of the air. However, changes in atmospheric dynamics also influence the magnitude and distribution of humidity trends. The homogenised modified Australian radiosonde data for the 850-hPa level show that the amount of moisture at this level increased ~8.8% °C–1 during 1965–2015
Biases in the thermodynamic structure over the Southern Ocean in ERA5 and their radiative implications
Publisher: Wiley
Date: 29-04-2022
DOI: 10.1002/JOC.7672
Abstract: The thermodynamic structure of the lower troposphere in the 37 standard levels ERA5 reanalysis has been evaluated against 2,186 high‐resolution upper air soundings collected over the Southern Ocean (SO). The reanalysis, which incorporated these soundings, was found to be skilled in depicting the general synoptic meteorology and thermodynamic structure as defined by the cluster analysis of Truong et al. (2020) Journal of Geophysical Research: Atmospheres , 125, e2020JD033214. Using dew‐point depression as a proxy for cloud, however, we found a significant reduction in the number of inferred cloud layers, which is inherited from a bias in the specific humidity in the ERA5 reanalysis, most notably over the high latitudes of the SO, where a multilayer cloud structure is frequently observed. The reanalysis was also found to have thinner inferred cloud geometric layer and shallower cloud top heights. Further analysis showed that the reanalysis displays a greater percentage of soundings having no inversion with this bias being more pronounced at high latitudes that tends to be associated with the colder sea surface temperature. While the statistics of the main inversion height are largely consistent, the average inversion strength in the ERA5 reanalysis is found to be weaker than the observations. We anticipate the 137‐level ERA5 reanalysis simulation yields a smoothed vertical structure, from which the 37 standard levels ERA5 reanalysis is linearly interpolated. An examination of the sensitivity of the radiative transfer to cloud macrophysics suggests that the correct representation of thin multiple cloud layers can help reduce the amount of downward shortwave surface radiation over the SO.
Evaluation of boundary-layer cloud forecasts over the Southern Ocean in a limited-area numerical weather prediction system usingin situ, space-borne and ground-based observations
Publisher: Wiley
Date: 10-03-2015
DOI: 10.1002/QJ.2519
A Climatology of the Precipitation over the Southern Ocean as Observed at Macquarie Island
Publisher: American Meteorological Society
Date: 12-2015
Abstract: Macquarie Island (54.50°S, 158.94°E) is an isolated island with modest orography in the midst of the Southern Ocean with precipitation records dating back to 1948. These records (referred to as MAC) are of particular interest because of the relatively large biases in the energy and water budgets commonly found in climate simulations and reanalysis products over the region. A basic climatology of the surface precipitation P is presented and compared with the ERA-Interim (ERA-I) reanalysis. The annual ERA-I precipitation (953 mm) is found to underestimate the annual MAC precipitation (1023 mm) by 6.8% from 1979 to 2011. The frequency of 3-h surface precipitation at MAC is 36.4% from 2003 to 2011. Light precipitation (0.066 ≤ P 0.5 mm h −1 ) dominates this dataset (29.7%), and heavy precipitation ( P ≥ 1.5 mm h −1 ) is rare (1.1%). Drizzle (0 P 0.066 mm h −1 ) is commonly produced by ERA-I (43.9%) but is weaker than the detectable threshold of MAC. Warm rain intensity and frequency from CloudSat products were compared with those from MAC. These CloudSat products also recorded considerable drizzle (16%–30%) but were not significantly different from MAC when P ≥ 0.5 mm h −1 . Heavy precipitation events were, in general, more commonly associated with fronts and cyclonic lows. Some heavy precipitation events were found to arise from weaker fronts and lows that were not adequately represented in the reanalysis products. Yet other heavy precipitation events were observed at points/times not associated with either fronts or cyclonic lows. Two case studies are employed to further examine this finding.
Dynamical and thermodynamical interactions in daily precipitation regimes in the Western Himalayas
Publisher: Wiley
Date: 04-01-2022
DOI: 10.1002/JOC.7511
Abstract: The mechanisms by which moisture interacts with the Himalayas largely determine the amount of precipitation in Himalayan basins. While many recent studies have focused on mechanisms of independent precipitation events, climatological studies that are essential for a complete understanding of precipitation‐generating mechanisms are limited. This work presents synoptic regimes, which produced precipitation across all seasons in the Western Himalayas (WH) from 2000 to 2018. Using the k‐means clustering algorithm, seven clusters are employed to define relatively mild, moderate and wet regimes, showing distinct seasonality and a synoptic meteorology. We found positive precipitation anomalies at lower elevations in monsoonal regimes (M1, M2 and M3) but at higher elevations in winter (W1 and W2) and transitional regimes (T1 and T2). Moist monsoonal regimes are associated with dynamical interactions between low‐level tropical cyclonic circulations and mid‐level subtropical troughs. Synchronous primary and secondary cyclonic circulations facilitate tropical moisture influx and obstruct the further northward movement of cyclonic circulations, which results in large magnitudes of precipitation at lower elevations in monsoonal regimes. On the other hand, winter regimes exhibit intense western disturbances, which enable orographic ascent of tropical moisture towards higher elevations. Despite weaker dynamical interactions, a stronger thermodynamical instability and a steeper terrain gradient trigger deep convection at higher elevations in transitional regimes. Overall, monsoonal regimes account for 52% of rainy days, whereas winter and transitional regimes account for 20 and 28%, respectively. We present a methodology that identifies hotspots of anomalous precipitation over vulnerable higher elevations by tracking atmospheric variables in Delhi. Our results illustrate the dynamical and thermodynamical interactions responsible for precipitation and highlight the significant contribution from nonmonsoonal regimes to the precipitation across higher elevations in the WH.
A comparison of cloud microphysical properties derived from MODIS and CALIPSO with in-situ measurements over the wintertime Southern Ocean
Publisher: American Geophysical Union (AGU)
Date: 03-10-2018
DOI: 10.1029/2018JD028535
A short climatology of nanoparticles at the Cape Grim Baseline Air Pollution Station, Tasmania
Publisher: CSIRO Publishing
Date: 2007
DOI: 10.1071/EN07038
Abstract: Environmental context. Atmospheric particles play an important role in the global climate system they contribute to the radiation balance directly, but they also have an indirect effect by modifying cloud properties and influencing precipitation. Over the Southern Ocean, nanometre-sized particle production is believed to be largely natural, although the processes that lead to these particles are not well understood. This work provides new observations of atmospheric nanoparticles, and shows that they arise from erse sources of production. Abstract. This paper presents analyses of a two-year record of aerosol measurements made at the Cape Grim Baseline Air Pollution Station (CGBAPS) in Tasmania covering the period 1999 and 2000. The focus of the study is nanoparticles, defined here as particles with diameter Dp, in the range 3 ≤ Dp ≤ 12 nm with the number concentration determined using two condensation particle counters, a TSI 3025 UCPC (Dp ≥ 3 nm) and a TSI CN3760 (Dp ≥ 12 nm). Total aerosol (Dp ≥ 3 nm) and nanoparticle concentrations were examined for three broad air mass origins, namely ‘Baseline’ or background maritime, continental Australia and Tasmanian air masses. Total median aerosol concentrations in the Baseline, continental and Tasmanian sectors typically ranged from 100 to 900, 1300 to 1900 and 500 to 1200 cm–3, respectively. The median ranges for the nanoparticle concentrations were 50–350 cm–3 in Baseline air, 150–450 cm–3 in continental air and 100–300 cm–3 in Tasmanian air. While the total aerosol concentrations in the three sectors were quite different, the nanoparticle concentrations were less so. Nanoparticle diurnal concentrations showed substantial differences between the three sectors, indicative of different aerosol sources or precursor sources in the regions designated by these wind sectors.
In situ observations of supercooled liquid clouds over the Southern Ocean during the HIAPER Pole‐to‐Pole Observation campaigns
Publisher: American Geophysical Union (AGU)
Date: 03-10-2013
DOI: 10.1002/GRL.50986
Buoyancy reversal and cloud‐top entrainment instability
Publisher: Wiley
Date: 04-1990
A Numerical Investigation of Cloud‐Top Entrainment Instability and Related Experiments
Publisher: Wiley
Date: 07-1992
Observations of Wind-Direction Variability in the Nocturnal Boundary Layer
Publisher: Springer Science and Business Media LLC
Date: 07-09-2017
Evaluating Himawari-8 Cloud Products Using Shipborne and CALIPSO Observations: Cloud-top Height and Cloud-top Temperature
Publisher: American Meteorological Society
Date: 12-2019
DOI: 10.1175/JTECH-D-18-0231.1
Abstract: Cloud-top height (CTH) and cloud-top temperature (CTT) retrieved from the Himawari-8 observations are evaluated using the active shipborne radar–lidar observations derived from the 31-day Clouds, Aerosols, Precipitation Radiation and Atmospheric Composition over the Southern Ocean (CAPRICORN) experiment in 2016 and 1-yr observations from the spaceborne Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) cloud product over a large sector of the Southern Ocean. The results show that the Himawari-8 CTH (CTT) retrievals agree reasonably well with both the shipborne estimates, with a correlation coefficient of 0.837 (0.820), a mean bias error of 0.226 km (−2.526°C), and an RMSE of 1.684 km (10.069°C). In the comparison with CALIOP, the corresponding quantities are found to be 0.786 (0.480), −0.570 km (1.343°C), and 2.297 km (25.176°C). The Himawari-8 CTH (CTT) generally falls between the physical CTHs observed by CALIOP and the shipborne radar–lidar estimates. However, major systematic biases are also identified. These errors include (i) a low (warm) bias in CTH (CTT) for warm liquid cloud type, (ii) a cold bias in CTT for supercooled liquid water cloud type, (iii) a lack of CTH at ~3 km that does not have a corresponding gap in CTT, (iv) a tendency of misclassifying some low-/mid-top clouds as cirrus and overlap cloud types, and (v) a saturation of CTH (CTT) around 10 km (−40°C), particularly for cirrus and overlap cloud types. Various challenges that underpin these biases are also explored, including the potential of parallax bias, low-level inversion, and cloud heterogeneity.
A Climatology of the Marine Atmospheric Boundary Layer Over the Southern Ocean From Four Field Campaigns During 2016–2018
Publisher: American Geophysical Union (AGU)
Date: 14-10-2020
DOI: 10.1029/2020JD033214
Evidence for secondary ice production in Southern Ocean open cellular convection
Publisher: Wiley
Date: 04-2017
DOI: 10.1002/QJ.3041
Regional sources of methyl chloride, chloroform and dichloromethane identified from AGAGE observations at Cape Grim, Tasmania, 1998-2000
Publisher: Springer Science and Business Media LLC
Date: 2003
On a Natural Environment for Glaciogenic Cloud Seeding
Publisher: American Meteorological Society
Date: 05-2013
Abstract: A “climatology” of supercooled cloud tops is presented for southeastern Australia and the western United States, where historic glaciogenic cloud-seeding trials have been located. The climatology finds that supercooled cloud tops are common over the mountainous region of southeastern Australia and Tasmania (SEAT). Regions where cloud-seeding trials reported positive results coincide with a higher likelihood of observing supercooled cloud tops. Maximum absolute frequencies (AFs) occur ∼40% of the time during winter. There is a relationship between the underlying orography and the likelihood of observing supercooled liquid water (SLW)-topped clouds. Regions of the United States that have been the subject of cloud-seeding trials show lower AFs of SLW-topped clouds. The maximum is located over the Sierra Nevada and occurs ∼20% of the time during winter (Sierra Cooperative Pilot Project). These sites are on mountains with peaks higher than any found in SEAT ( m). For the Sierra Nevada, the AF of SLW-topped clouds decreases as the elevation increases, with glaciation occurring at the higher elevations. The remote sensing of supercooled cloud tops is not proof of a region’s amenability for glaciogenic cloud seeding. This study simply highlights the significant environmental differences between historical cloud-seeding regions in the United States and Australia, suggesting that it is not reasonable to extrapolate results from one region to another. Without in situ cloud microphysical measurements, in-depth knowledge of the timing and duration of potentially seedable events, or knowledge of the synoptic forcing of such events, it is not possible to categorize a region’s potential for precipitation augmentation operations.
A Characterization of Clouds and Precipitation Over the Southern Ocean From Synoptic to Micro Scales During the CAPRICORN Field Campaigns
Publisher: American Geophysical Union (AGU)
Date: 12-09-2022
DOI: 10.1029/2022JD036796
Abstract: The persistent Southern Ocean (SO) shortwave radiation biases in climate models and reanalyses have been associated with the poor representation of clouds, precipitation, aerosols, the atmospheric boundary layer, and their intrinsic interactions. Capitalizing on shipborne observations collected during the Clouds Aerosols Precipitation Radiation and atmospheric Composition Over the Southern Ocean 2016 and 2018 field c aigns, this research investigates and characterizes cloud and precipitation processes from synoptic to micro scales. Distinct cloud and precipitation regimes are found to correspond to the seven thermodynamic clusters established using a K‐means clustering technique, while less distinctions are evident using the cyclone and (cold) front compositing methods. Cloud radar and disdrometer data reveal that light precipitation is common over the SO with higher intensities associated with cyclonic and warm frontal regions. Multiple lines of evidence suggest the presence of erse microphysical features in several cloud regimes, including the likely dominance of ice aggregation in deep precipitating clouds. Signatures of mixed phase, and in some cases, riming were detected in shallow convective clouds away from the frontal conditions. Two of the K‐means clusters with contrasting cloud and precipitation properties are observed over the high‐latitude SO and coastal Antarctica, suggesting distinct physical processes therein. Through a single case study, in‐situ and remote‐sensing data collected by an overflight of the Southern Ocean Clouds Radiation Aerosol Transport Experimental Study were also evaluated and complement the ship‐based analysis.
An evaluation of WRF simulations of clouds over the southern ocean with a-train observations
Publisher: American Meteorological Society
Date: 24-01-2014
Abstract: The representation of the marine boundary layer (BL) clouds remains a formidable challenge for state-of-the-art simulations. A recent study by Bodas-Salcedo et al. using the Met Office Unified Model highlights that the underprediction of the low/midlevel postfrontal clouds contributes to the largest bias of the surface downwelling shortwave radiation over the Southern Ocean (SO). A-Train observations and limited in situ measurements have been used to evaluate the Weather Research and Forecasting Model, version 3.3.1 (WRFV3.3.1), in simulating the postfrontal clouds over Tasmania and the SO. The simulated cloud macro/microphysical properties are compared against the observations. Experiments are also undertaken to test the sensitivity of model resolution, microphysical (MP) schemes, planetary boundary layer (PBL) schemes, and cloud condensation nuclei (CCN) concentration. The simulations demonstrate a considerable level of skill in representing the clouds during the frontal passages and, to a lesser extent, in the postfrontal environment. The simulations, however, have great difficulties in portraying the widespread marine BL clouds that are not immediately associated with fronts. This shortcoming is persistent to the changes of model configuration and physical parameterization. The representation of large-scale conditions and their connections with the BL clouds are discussed. A lack of BL moisture is the most obvious explanation for the shortcoming, which may be a consequence of either strong entrainment or weak surface fluxes. It is speculated that the BL wind shear/turbulence may be an issue over the SO. More comprehensive observations are necessary to fully investigate the deficiency of the simulations.
Cloud-System-Resolving Model Simulations of Tropical Cloud Systems Observed during the Tropical Warm Pool-International Cloud Experiment
Publisher: American Meteorological Society
Date: 2010
Abstract: Nested cloud-system-resolving model simulations of tropical convective clouds observed during the recent Tropical Warm Pool-International Cloud Experiment (TWP-ICE) are conducted using the Weather Research and Forecasting (WRF) model. The WRF model is configured with a highest-resolving domain that uses 1.3-km grid spacing and is centered over Darwin, Australia. The performance of the model in simulating two different convective regimes observed during TWP-ICE is considered. The first regime is characteristic of the active monsoon, which features widespread cloud cover that is similar to maritime convection. The second regime is a monsoon break, which contains intense localized systems that are representative of diurnally forced continental convection. Many aspects of the model performance are considered, including their sensitivity to physical parameterizations and initialization time, and the spatial statistics of rainfall accumulations and the rain-rate distribution. While the simulations highlight many challenges and difficulties in correctly modeling the convection in the two regimes, they show that provided the mesoscale environment is adequately reproduced by the model, the statistics of the simulated rainfall agrees reasonably well with the observations.
A characterization of clouds over the Great Barrier Reef and the role of local forcing
Publisher: Wiley
Date: 02-05-2022
DOI: 10.1002/JOC.7660
Abstract: A characterization of cloud properties associated with precipitation in the region around the Great Barrier Reef (GBR) is constructed using decade‐long (2007–2017) satellite observations from Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) combined with CloudSat. The spatial and vertical distributions of low‐level cloud properties over the region are also investigated and discussed. In general, different cloud types are observed over different regions and vary by season: high clouds are dominant over the low latitudes in summer, altocumulus are mainly observed over northeast Queensland and low‐level clouds are dominant over the ocean and coast during the winter months at higher latitudes under a trade wind regime. A strong latitudinal dependence of total precipitation across the Greater GBR region is identified with a significant orographic enhancement near Cairns in the wet tropics. MODIS and CloudSat‐CALIPSO cloud observations show good agreement on significant differences in low‐level cloud microphysical properties between the land and the ocean. The largest land–ocean differences in warm cloud microphysical properties are found over the mid‐latitudes near 18°S, which is strongly associated with orographic forcing, with these enhancements extending further east to the coral reef area. However, the frequency of warm cloud is not enhanced upwind of the mountains in the wet tropics. In addition, no significant differences in warm cloud properties between the actual GBR and the open ocean are identified. These results suggest that low‐level clouds over the GBR do not show any significant response to the reef‐related microphysical perturbations.
Lidar ratios of stratospheric volcanic ash and sulfate aerosols retrieved from CALIOP measurements
Publisher: Copernicus GmbH
Date: 14-07-2017
Abstract: Abstract. We apply a two-way transmittance constraint to nighttime CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) observations of volcanic aerosol layers to retrieve estimates of the particulate lidar ratio (Sp) at 532 nm. This technique is applied to three volcanic eruption case studies that were found to have injected aerosols directly into the stratosphere. Numerous lidar observations permitted characterization of the optical and geometric properties of the volcanic aerosol layers over a time period of 1–2 weeks. For the volcanic ash-rich layers produced by the Puyehue-Cordón Caulle eruption (June 2011), we obtain mean and median particulate lidar ratios of 69 ± 13 sr and 67 sr, respectively. For the sulfate-rich aerosol layers produced by Kasatochi (August 2008) and Sarychev Peak (June 2009), the means of the retrieved lidar ratios were 66 ± 19 sr (median 60 sr) and 63 ± 14 sr (median 59 sr), respectively. The 532 nm layer-integrated particulate depolarization ratios (δp) observed for the Puyehue layers (δp = 0.33 ± 0.03) were much larger than those found for the volcanic aerosol layers produced by the Kasatochi (δp = 0.09 ± 0.03) and Sarychev (δp = 0.05 ± 0.04) eruptions. However, for the Sarychev layers we observe an exponential decay (e-folding time of 3.6 days) in δp with time from 0.27 to 0.03. Similar decreases in the layer-integrated attenuated colour ratios with time were observed for the Sarychev case. In general, the Puyehue layers exhibited larger colour ratios (χ′ = 0.53 ± 0.07) than what was observed for the Kasatochi (χ′ = 0.35 ± 0.07) and Sarychev (χ′ = 0.32 ± 0.07) layers, indicating that the Puyehue layers were generally composed of larger particles. These observations are particularly relevant to the new stratospheric aerosol subtyping classification scheme, which has been incorporated into version 4 of the level 2 CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) data products.
Estimation of Wind-Induced Losses from a Precipitation Gauge Network in the Australian Snowy Mountains
Publisher: American Meteorological Society
Date: 17-11-2015
Abstract: Wind-induced losses, or undercatch, can have a substantial impact on precipitation gauge observations, especially in alpine environments that receive a substantial amount of frozen precipitation and may be exposed to high winds. A network of NOAH II all-weather gauges installed in the Snowy Mountains since 2006 provides an opportunity to evaluate the magnitude of undercatch in an Australian alpine environment. Data from two intercomparison sites were used with NOAH II gauges with different configurations of wind fences installed: unfenced, WMO standard double fence intercomparison reference (full DFIR) fences, and an experimental half-sized double fence (half DFIR). It was found that average ambient temperature over 6-h periods was sufficient to classify the precipitation phase as snow, mixed precipitation, or rain in a statistically robust way. Empirical catch ratio relationships (i.e., the quotient of observations from two gauges), based on wind speed, ambient temperature, and measured precipitation amount, were established for snow and mixed precipitation. An adjustment scheme to correct the unfenced NOAH II gauge data using the catch ratio relationships was cross validated with independent data from two additional sites, as well as from the intercomparison sites themselves. The adjustment scheme was applied to the observed precipitation amounts at the other sites with unfenced NOAH II gauges. In the worst-case scenario, it was found that the observed precipitation amount would need to be increased by 52% to match what would have been recorded had adequate shielding been installed. However, gauges that were naturally well protected, and those below about 1400 m, required very little adjustment. Spatial analysis showed that the average seasonal undercatch was between 6% and 15% for gauges above 1000 m MSL.
Wintertime orographic precipitation over western Tasmania
Publisher: CSIRO Publishing
Date: 31-12-2018
DOI: 10.22499/3.6801.003
Prediction and observation of cloud processing of the aerosol size distribution by a band of cumulus
Publisher: Wiley
Date: 04-2006
DOI: 10.1256/QJ.05.106
Observations of Supercooled Liquid Water in Wintertime Alpine Storms in South Eastern Australia
Publisher: Elsevier BV
Date: 03-2016
Inter‐decadal change of leading pattern of spring rainfall over southern China during 1901–2010
Publisher: Wiley
Date: 18-04-2018
DOI: 10.1002/JOC.5511
Towards a better understanding of fog at Perth Airport
Publisher: Elsevier BV
Date: 09-2021
Observations of Clouds, Aerosols, Precipitation, and Surface Radiation over the Southern Ocean: An Overview of CAPRICORN, MARCUS, MICRE, and SOCRATES
Publisher: American Meteorological Society
Date: 04-2021
Abstract: Weather and climate models are challenged by uncertainties and biases in simulating Southern Ocean (SO) radiative fluxes that trace to a poor understanding of cloud, aerosol, precipitation, and radiative processes, and their interactions. Projects between 2016 and 2018 used in situ probes, radar, lidar, and other instruments to make comprehensive measurements of thermodynamics, surface radiation, cloud, precipitation, aerosol, cloud condensation nuclei (CCN), and ice nucleating particles over the SO cold waters, and in ubiquitous liquid and mixed-phase clouds common to this pristine environment. Data including soundings were collected from the NSF–NCAR G-V aircraft flying north–south gradients south of Tasmania, at Macquarie Island, and on the R/V Investigator and RSV Aurora Australis . Synergistically these data characterize boundary layer and free troposphere environmental properties, and represent the most comprehensive data of this type available south of the oceanic polar front, in the cold sector of SO cyclones, and across seasons. Results show largely pristine environments with numerous small and few large aerosols above cloud, suggesting new particle formation and limited long-range transport from continents, high variability in CCN and cloud droplet concentrations, and ubiquitous supercooled water in thin, multilayered clouds, often with small-scale generating cells near cloud top. These observations demonstrate how cloud properties depend on aerosols while highlighting the importance of dynamics and turbulence that likely drive heterogeneity of cloud phase. Satellite retrievals confirmed low clouds were responsible for radiation biases. The combination of models and observations is examining how aerosols and meteorology couple to control SO water and energy budgets.
Evidence of a Diurnal Cycle in Precipitation over the Southern Ocean as Observed at Macquarie Island
Publisher: MDPI AG
Date: 09-02-2020
Abstract: Due to a lack of observations, relatively large discrepancies exist between precipitation products over the Southern Ocean. In this manuscript, surface hourly precipitation observations from Macquarie Island (54.62 ° S, 158.85 ° E) are analysed (1998–2016) to reveal a diurnal cycle. The precipitation rate is at a maximum during night/early morning and a minimum in the afternoon at Macquarie Island station. Seasonally, the diurnal cycle is strongest in summer and negligible over winter. Such a cycle is consistent with precipitation arising from marine boundary layer clouds, suggesting that such clouds are making a substantial contribution to total precipitation over Macquarie Island and the Southern Ocean. Using twice daily upper air soundings (1995–2011), lower troposphere stability parameters show a stronger inversion at night, again consistent with precipitation arising from marine boundary layer clouds. The ERA-Interim precipitation is dominated by a 12 hourly cycle, year around, which is likely to be a consequence of the twice-daily initialisation. The implication of a diurnal cycle in boundary layer clouds over the Southern Ocean to derived A-Train satellite precipitation products is also discussed.
Statistical Assessment of Tropical Convection-Permitting Model Simulations Using a Cell-Tracking Algorithm
Publisher: American Meteorological Society
Date: 02-2013
Abstract: This study presents a method for comparing convection-permitting model simulations to radar observations using an innovative object-based approach. The method uses the automated cell-tracking algorithm, Thunderstorm Identification Tracking Analysis and Nowcasting (TITAN), to identify in idual convective cells and determine their properties. Cell properties are identified in the same way for model and radar data, facilitating comparison of their statistical distributions. The method is applied to simulations of tropical convection during the Tropical Warm Pool-International Cloud Experiment (TWP-ICE) using the Weather Research and Forecasting Model, and compared to data from a ground-based radar. Simulations with different microphysics and model resolution are also conducted. Among other things, the comparisons between the model and the radar elucidate model errors in the depth and size of convective cells. On average, simulated convective cells reached higher altitudes than the observations. Also, when using a low reflectivity (25 dBZ) threshold to define convective cells, the model underestimates the size of the largest cells in the observed population. Some of these differences are alleviated with a change of microphysics scheme and higher model resolution, demonstrating the utility of this method for assessing model changes.
Observed Trends in Wind Speed over the Southern Ocean
Publisher: American Geophysical Union (AGU)
Date: 06-2012
DOI: 10.1029/2012GL051734
Application of The Air Pollution Model (TAPM) to the urban airshed of Bangkok, Thailand
Publisher: Inderscience Publishers
Date: 2010
Estimation of Daily Winter Precipitation in the Snowy Mountains of Southeastern Australia
Publisher: American Meteorological Society
Date: 06-2014
Abstract: Wintertime precipitation in the Snowy Mountains provides water for agriculture, industry, and domestic use in inland southeastern Australia. Unlike most of Australia, much of this precipitation falls as snow, and it is recorded by a private network of heated tipping-bucket gauges. These observations are used in the present study to assess the accuracy of a poor man’s ensemble (PME) prediction of precipitation in the Snowy Mountains based on seven numerical weather prediction models. While the PME performs quite well, there is significant underestimation of precipitation intensity. It is shown that indicators of the synoptic environment can be used to improve the PME estimates of precipitation. Four synoptic regimes associated with different precipitation classes are identified from upper-air data. The reliability of the PME forecasts can be sharpened by considering the precipitation in each of the four synoptic classes. A linear regression, based on the synoptic classification and the PME estimate, is used to reduce the forecast errors. The potential to extend the method for forecasting purposes is discussed.
A study on the low-altitude clouds over the Southern Ocean using the DARDAR-MASK
Publisher: American Geophysical Union (AGU)
Date: 21-09-2012
DOI: 10.1029/2012JD017800
A characterization of clouds and precipitation over the Southern Ocean from synoptic to micro scales during the CAPRICORN field campaigns
Publisher: Wiley
Date: 22-03-2022
Observations of wind shear over the Southern Ocean
Publisher: American Geophysical Union (AGU)
Date: 27-06-2012
DOI: 10.1029/2012JD017488
Polarimetric Backscatter Sonde Observations of Southern Ocean Clouds and Aerosols
Publisher: MDPI AG
Date: 17-04-2020
Abstract: Balloon-borne polarimetric backscatter sonde (polarsonde) observations of aerosol and cloud during the approach of a cold front at Macquarie Island (54.499 S 158.937 E) are described. The polarsonde captures vertical profiles of cloud occurrence and phase. The cloud base and cloud top heights from the backscatter sonde compare favourably with observations made by a co-located cloud radar and ceilometer. An estimate of the total scatter probability from a liquid cloud layer at 1000 m height is used with a Monte Carlo model of the instrument to obtain cloud particle concentration, and this is compared to a measurement of cloud condensation nucleus concentration made at sea level. Backscatter from aerosol, as well as cloud, is significant. A high aerosol loading in part of the pre-frontal airmass is observed at altitudes up to 6 km. Below the melting level, the high cross-polarised return, relative to the co-polarised, indicates a substantial concentration of solid, non-spherical aerosol particles, which due to the high humidity cannot be sea salt or sulphate. A back trajectory analysis indicates that the observed aerosol includes continental dust.
Identification of Regional Sources of Methyl Bromide and Methyl Iodide from AGAGE Observations at Cape Grim, Tasmania
Publisher: Springer Science and Business Media LLC
Date: 2005
What is the role of sea surface temperature in modulating cloud and precipitation properties over the Southern Ocean?
Publisher: American Meteorological Society
Date: 28-09-2016
Abstract: This study employs four years of spatiotemporally collocated A-Train satellite observations to investigate cloud and precipitation characteristics in relation to the underlying properties of the Southern Ocean (SO). Results show that liquid-phase cloud properties strongly correlate with the sea surface temperature (SST). In summer, ubiquitous supercooled liquid water (SLW) is observed over SSTs less than about 4°C. Cloud-top temperature (CTT) and effective radius of liquid-phase clouds generally decrease for colder SSTs, whereas the opposite trend is observed for cloud-top height, cloud optical thickness, and liquid water path. The deduced cloud depth is larger over the colder oceans. Notable differences are observed between “precipitating” and “nonprecipitating” clouds and between different ocean sectors. Using a novel joint SST–CTT histogram, two distinct liquid-phase cloud types are identified, where the retrieved particle size appears to increase with decreasing CTT over warmer water (SSTs & ~7°C), while the opposite is true over colder water. A comparison with the Northern Hemisphere (NH) storm-track regions suggests that the ubiquitous SLW with markedly smaller droplet size is a unique feature for the cold SO (occurring where SSTs & ~4°C), while the presence of this cloud type is much less frequent over the NH counterparts, where the SSTs are rarely colder than about 4°C at any time of the year. This study also suggests that precipitation, which has a profound influence on cloud properties, remains poorly observed over the SO with the current spaceborne sensors. Large uncertainties in precipitation properties are associated with the ubiquitous boundary layer clouds within the lowest kilometer of the atmosphere.
An evaluation of kilometer-scale ICON simulations of mixed-phase stratocumuli over the Southern Ocean during CAPRICORN
Publisher: Wiley
Date: 05-12-2022
Homogenized monthly upper‐air temperature data set for Australia
Publisher: Wiley
Date: 25-11-2016
DOI: 10.1002/JOC.4909
Postfrontal nanoparticles at Cape Grim: observations
Publisher: CSIRO Publishing
Date: 2009
DOI: 10.1071/EN09075
Abstract: Environmental context. Clouds and the factors controlling cloud properties are essential components in understanding and accurately predicting global climate change. This work examines nanometre-sized atmospheric particles, particularly bursts of enhanced particle concentrations following cold fronts over the Southern Ocean. The properties of these events have been established to enable modelling of their significance as a source of cloud-droplet-forming nuclei. Abstract. Nanoparticles (diameter nm) were studied in clean maritime air at Cape Grim over a 2-year period. Concentrations were determined using a condensation nucleus counter (CNC) and an ultra-CNC (UCNC), requiring careful treatment of drifts in counter efficiency. This is the first extended examination of nanoparticles following cold fronts and shows that nanoparticle enhancements were present following 94% of 121 cold fronts studied. Typical enhancements were ~100 cm–3 with maxima ~300–500 cm–3, occur 9–11 h after the front and contain multiple peaks with peak-to-peak separation of 8–11 h. Most enhancements were associated with drier conditions, indicative of increased entrainment of free-tropospheric air after the front. The quasi-periodicity of the enhancements may be related to mesoscale structures in cloud fields following fronts but this requires testing. This quantification of event properties allows evaluation of the significance of these events for the cloud nucleating particle (CCN) population.
Objective Classification of Precipitating Convective Regimes Using a Weather Radar in Darwin, Australia
Publisher: American Meteorological Society
Date: 05-2009
Abstract: A clustering algorithm was applied to Frequency with Altitude Diagrams (FADs) derived from 4 yr of hourly radar data to objectively define four tropical precipitation regimes that occur during the wet season over Darwin Australia. The precipitation regimes defined are distinguished in terms of convective intensity, presence of stratiform precipitation, and precipitation coverage. Regime 1 consists of patchy convection of medium intensity and low area coverage, and regime 2 contains strong convection with relatively small area coverage. Regime 3 is composed of weak convection with large area coverage and large stratiform regions, and regime 4 contains strong convection with large area coverage and large stratiform regions. Analysis of the seasonal cycle, diurnal cycle, and regime occurrence as a function of monsoon activity all provide insight into the different physical character of the precipitation regimes. Two of the regimes exhibit a diurnal cycle with a peak in the afternoon, while the other two show a peak in their frequency of occurrence in the early morning. The different character of the regimes is also confirmed by the varying contributions that convective and stratiform rainfall make to the overall within-regime precipitation.
Southern Ocean precipitation: Toward a process‐level understanding
Publisher: Wiley
Date: 12-09-2022
DOI: 10.1002/WCC.800
Abstract: Large differences continue to exist between current precipitation products over the Southern Ocean (SO). This limits our ability to close the hydrological cycle over the SO and Antarctica, as well as limiting our understanding of a range of climatological and meteorological processes. This uncertainty arises from the absence of long‐term, high‐quality surface observational records of precipitation suitable for evaluation across a range of temporal and spatial scales. We have no “truth” for precipitation across this region that covers ~15% of the Earth's surface. These differences extend to spatial and temporal distributions and trends. Precipitation products that have been calibrated and evaluated against established observations in the Northern Hemisphere potentially may be biased due to fundamental differences in the dynamics and microphysics over the remote SO. This review first considers recent advances in our understanding of the precipitation of the SO, including spatial and temporal variability, thermodynamic phase, and response to climate drivers. We then examine several commonly used precipitation products derived from satellite observations (both passive and active), reanalyses, and merged products. Where possible, we examine the skill of these products across a range of precipitation processes that commonly occur across the SO. Finally, we look briefly at the potential of new resources, such as dual‐polarized radars and maritime disdrometers, that can be used in field c aigns specifically designed to observe precipitation at the process level, and ultimately used to evaluate precipitation products over the SO. This article is categorized under: Paleoclimates and Current Trends Earth System Behavior Paleoclimates and Current Trends Climate Forcing
Cloudiness and Marine Boundary Layer Dynamics in the ASTEX Lagrangian Experiments. Part II: Cloudiness, Drizzle, Surface Fluxes, and Entrainment
Publisher: American Meteorological Society
Date: 08-1995
Characteristics of marine boundary layers during two Lagrangian measurement periods: 1. General conditions and mean characteristics
Publisher: American Geophysical Union (AGU)
Date: 09-1999
DOI: 10.1029/1998JD100099
Characteristics of wintertime daily precipitation over the Australian Snowy Mountains
Publisher: American Meteorological Society
Date: 10-2017
Abstract: The relationship between orographic precipitation, low-level thermodynamic stability, and the synoptic meteorology is explored for the Snowy Mountains of southeast Australia. A 21-yr dataset (May–October, 1995–2015) of upper-air soundings from an upwind site is used to define synoptic indicators and the low-level stability. A K-means clustering algorithm was employed to classify the daily meteorology into four synoptic classes. The initial classification, based only on six synoptic indicators, distinctly defines both the surface precipitation and the low-level stability by class. Consistent with theory, the wet classes are found to have weak low-level stability, and the dry classes have strong low-level stability. By including low-level stability as an additional input variable to the clustering method, statistically significant correlations were found between the precipitation and the low-level stability within each of the four classes. An examination of the joint PDF reveals a highly nonlinear relationship heavy rain was associated with very weak low-level stability, and conversely, strong low-level stability was associated with very little precipitation. Building on these historical relationships, model output statistics (MOS) from a moderate resolution (12-km spatial resolution) operational forecast were used to develop stepwise regression models designed to improve the 24-h forecast of precipitation over the Snowy Mountains. A single regression model for all days was found to reduce the RMSE by 7% and the bias by 75%. A class-based regression model was found to reduce the overall RMSE by 30% and the bias by 85%.
Air‐Sea Heat and Momentum Fluxes in the Southern Ocean
Publisher: American Geophysical Union (AGU)
Date: 03-12-2019
DOI: 10.1029/2018JD029761
Abstract: The Clouds, Aerosols, Precipitation, Radiation, and atmospherIc Composition Over the southeRn oceaN (CAPRICORN) experiment was carried out in March–April 2016 onboard R/V Investigator studying momentum ( τ ), sensible heat ( H s ), and latent heat ( H l ) fluxes over the Australian sector of the Southern Ocean including over one cyclonic cold‐core and one anticyclonic warm‐core mesoscale oceanic eddy. The turbulence‐based flux measurements obtained with the NOAA PSD flux system employing eddy covariance (EC) and inertial dissipation (ID) methods are compared with those obtained by the Coupled Ocean‐Atmosphere Response Experiment (COARE) 3.5 bulk model, and the neutral transfer coefficients are studied. The relative uncertainty between the turbulence‐based and COARE 3.5 estimates of τ , H s , and H l are 22%, 70%, and 26%, respectively, at 1‐hr time scale over the Southern Ocean. Further, the variability in bulk fluxes is investigated with respect to oceanic eddies, precipitation events, atmospheric stability, and extratropical cyclones encountered during the voyage. The main observed variability is an increase in significant wave height or γ w (∼33%), τ (∼89%), H s (∼187%), and H l (∼79%) over the warm eddy as compared to average voyage values. During the passage of six extratropical cyclones, an increase in τ (∼62% average) and a decrease in H s (∼235%) and H l (∼79%) is noted in the warm sector, compared to prestorm conditions, but the pattern reverses behind the cold front.
Wintertime precipitation over the Australian Snowy Mountains: Observations from an Intensive Field Campaign 2018
Publisher: American Meteorological Society
Date: 07-2021
Abstract: Understanding the key dynamical and microphysical mechanisms driving precipitation in the Snowy Mountains region of southeast Australia, including the role of orography, can help improve precipitation forecasts, which is of great value for efficient water management. An intensive observation c aign was carried out during the 2018 austral winter, providing a comprehensive range of ground-based observations across the Snowy Mountains. We used data from three vertically pointing rain radars, cloud radar, a PARSIVEL disdrometer, and a network of 76 pluviometers. The observations reveal that all of the precipitation events were associated with cold front passages. About half accumulated during the frontal passage associated with deep, fully glaciated cloud tops while the rest occurred in the post-frontal environment and was associated with clouds with supercooled liquid water (SLW) tops. About three quarters of the accumulated precipitation were observed under blocked conditions, likely associated with blocked stratiform orographic enhancement. Specifically, more than a third of the precipitation resulted from moist cloudless air being lifted over stagnant air, upwind from the barrier, creating SLW-top clouds. These SLW-clouds then produced stratiform precipitation mostly over the upwind slopes and mountain tops, with hydrometeors reaching the mountain tops mostly as rimed snow. Two precipitation events were studied in detail, which showed that during unblocked conditions, orographic convection invigoration and unblocked stratiform enhancement were the two main mechanisms driving the precipitation with the latter being more prevalent after the frontal passage. During these events, ice particle growth was likely dominated by vapor deposition and aggregation during the frontal periods, while riming dominated during the post-frontal periods.
A Three-Year Climatology of Cloud-Top Phase over the Southern Ocean and North Pacific
Publisher: American Meteorological Society
Date: 05-2011
Abstract: Moderate Resolution Imaging Spectroradiometer (MODIS) Level 2 observations from the Terra satellite are used to create a 3-yr climatology of cloud-top phase over a section of the Southern Ocean (south of Australia) and the North Pacific Ocean. The intent is to highlight the extensive presence of supercooled liquid water over the Southern Ocean region, particularly during summer. The phase of such clouds directly affects the absorbed shortwave radiation, which has recently been found to be “poorly simulated in both state-of-the-art reanalysis and coupled global climate models” (Trenberth and Fasullo). The climatology finds that supercooled liquid water is present year-round in the low-altitude clouds across this section of the Southern Ocean. Further, the MODIS cloud phase algorithm identifies very few glaciated cloud tops at temperatures above −20°C, rather inferring a large portion of “uncertain” cloud tops. Between 50° and 60°S during the summer, the albedo effect is compounded by a seasonal reduction in high-level cirrus. This is in direct contrast to the Bering Sea and Gulf of Alaska. Here MODIS finds a higher likelihood of observing warm liquid water clouds during summer and a reduction in the relative frequency of cloud tops within the 0° to −20°C temperature range. As the MODIS cloud phase product has limited ability to confidently identify cloud-top phase between −5° and −25°C, future research should include observations from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and other space-based sensors to help with the classification within this temperature range. Further, multiregion in situ verification of any remotely sensed observations is vital to further understanding the cloud phase processes.
Sensitivity of the orographic precipitation across the Australian Snowy Mountains to regional climate indices
Publisher: CSIRO Publishing
Date: 2019
DOI: 10.1071/ES19014
Abstract: The wintertime (May–October) precipitation across south-eastern Australia, and the Snowy Mountains, was studied for 22 years (1995–2016) to explore the sensitivity of the relationships between six established climate indices and the precipitation to the orography, both regionally and locally in high-elevation areas. The high-elevation (above 1100 m) precipitation records were provided by an independent network of rain gauges maintained by Snowy Hydro Ltd. These observations were compared with the Australian Water Availability Project (AWAP) precipitation analysis, a commonly used gridded nationwide product. As the AWAP analysis does not incorporate any high-elevation sites, it is unable to capture local orographic precipitation processes. The analysis demonstrates that the alpine precipitation over the Snowy Mountains responds differently to the indices than the AWAP precipitation. In particular, the alpine precipitation is found to be most sensitive to the position of the subtropical ridge and less sensitive to a number of other climate indices tested. This sensitivity is less evident in the AWAP representation of the high-elevation precipitation. Regionally, the analysis demonstrates that the precipitation to the east of the Snowy Mountains (the downwind precipitation) is weakly correlated with the upwind and peak precipitation. This is consistent with previous works that found that the precipitation in this downwind region commonly occurs from mechanisms other than storm systems passing over the mountains.
Relationship between rainfall and weather regimes in south‐eastern Queensland, Australia
Publisher: Wiley
Date: 11-04-2012
DOI: 10.1002/JOC.3484
Evaluation of wintertime precipitation forecasts over the Australian Snowy Mountains
Publisher: Elsevier BV
Date: 07-2018
Evaluation of the AWAP daily precipitation spatial analysis with an independent gauge network in the Snowy Mountains
Publisher: CSIRO Publishing
Date: 2016
DOI: 10.22499/3.6601.006
Cloud Seeding
Publisher: Springer Netherlands
Date: 2013
A-Train observations of maritime midlatitude storm-track cloud systems: Comparing the Southern Ocean against the North Atlantic
Publisher: American Meteorological Society
Date: 26-02-2015
DOI: 10.1175/JCLI-D-14-00169.1
Abstract: Cloud and precipitation properties of the midlatitude storm-track regions over the Southern Ocean (SO) and North Atlantic (NA) are explored using reanalysis datasets and A-Train observations from 2007 to 2011. In addition to the high-level retrieval products, lower-level observed variables—CloudSat radar reflectivity and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar attenuated backscatter—are directly examined using both contoured frequency by altitude diagrams (CFADs) and contoured frequency by temperature diagrams (CFTDs) to provide direct insight into thermodynamic phase properties. While the wintertime temperature profiles are similar over the two regions, the summertime environment is warmer over the NA. The NA atmosphere is generally moister than the SO, while the SO boundary layer is moister during winter. The results herein suggest that although the two regions exhibit many similarities in the prevalence of boundary layer clouds (BLCs) and frontal systems, notable differences exist. The NA environment exhibits stronger seasonality in thermodynamic structure, cloud, and precipitation properties than the SO. The regional differences of cloud properties are dominated by microphysics in winter and thermodynamics in summer. Glaciated clouds with higher reflectivities are found at warmer temperatures over the NA. BLCs (primarily below 1.5 km) are a predominant component over the SO. The wintertime boundary layer is shallower over the SO. Midlevel clouds consisting of smaller hydrometeors in higher concentration (potentially supercooled liquid water) are more frequently observed over the SO. Cirrus clouds are more prevalent over the NA. Notable differences exist in both the frequencies of thermodynamic phases of precipitation and intensity of warm rain over the two regions.
The Role of Clouds in Coral Bleaching Events Over the Great Barrier Reef
Publisher: American Geophysical Union (AGU)
Date: 28-07-2021
DOI: 10.1029/2021GL093936
Abstract: Thermal coral bleaching events (CBEs) over the Pacific, including those over the Great Barrier Reef (GBR), have commonly been linked to the El Niño–Southern Oscillation (ENSO), with bleaching reported to be a direct result of sea surface temperature (SST) anomalies driven by El Niño. However, such a relationship cannot explain CBEs that occurred during La Niña or the neutral phase of the ENSO. Here, we show that the GBR is characterized by a significant negative correlation between total cloud cover anomaly (TCCA) and lagged SST anomaly (SSTA) whose magnitude and spatial extent are greater than the SSTA‐ENSO correlation. This significant negative TCCA‐SSTA (lagged) correlation prevails over two‐thirds of the study domain even after the ENSO signal is removed, which suggests that local‐scale reduced cloud cover is a key component of the regional warm shallow water formation over the GBR and the occurrence of thermal CBEs.
Improving discrimination between clouds and optically thick aerosol plumes in geostationary satellite data
Publisher: Copernicus GmbH
Date: 17-05-2022
Abstract: Abstract. Cloud masking is a key initial step in the retrieval of geophysical properties from satellite data. Despite decades of research, problems still exist of over- or underdetection of clouds. High aerosol loadings, in particular from dust storms or fires, are often classified as clouds, and vice versa. In this paper, we present a cloud mask created using machine learning for the Advanced Himawari Imager (AHI) aboard Himawari-8. In order to train the algorithm, a parallax-corrected collocated data set was created from AHI and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) lidar data. Artificial neural networks (ANNs) were trained on the collocated data to identify clouds in AHI scenes. The resulting neural network (NN) cloud masks are validated and compared to cloud masks produced by the Japanese Meteorological Association (JMA) and the Bureau of Meteorology (BoM) for a number of different solar and viewing geometries, surface types and air masses. Here, five case studies covering a range of challenging scenarios for cloud masks are also presented to demonstrate the performance of the masking algorithm. The NN mask shows a lower false positive rate (FPR) for an equivalent true positive rate (TPR) across all categories, with FPRs of 0.160 and 0.259 for the NN and JMA masks, respectively, and 0.363 and 0.506 for the NN and BoM masks, respectively, at equivalent TPR values. This indicates the NN mask accurately identifies 1.13 and 1.29 times as many non-cloud pixels for the equivalent hit rate when compared to the JMA and BoM masks, respectively. The NN mask was shown to be particularly effective in distinguishing thick aerosol plumes from cloud, most likely due to the inclusion of the 0.47 and 0.51 µm bands. The NN cloud mask shows an improvement over current operational cloud masks in most scenarios, and it is suggested that improvements to current operational cloud masks could be made by including the 0.47 and 0.51 µm bands. The collocated data are made available to facilitate future research.
The Queensland Cloud Seeding Research Program
Publisher: American Meteorological Society
Date: 2012
Simulation of orographic precipitation in the Snowy Mountain of Southeast Australia
Publisher: Elsevier BV
Date: 05-2019
The structure of low-altitude clouds over the Southern Ocean as seen by CloudSat
Publisher: American Meteorological Society
Date: 28-03-2012
DOI: 10.1175/JCLI-D-11-00131.1
Abstract: A climatology of the structure of the low-altitude cloud field (tops below 4 km) over the Southern Ocean (40°–65°S) in the vicinity of Australia (100°–160°E) has been constructed with CloudSat products for liquid water and ice water clouds. Averaging over longitude and time, CloudSat produces a roughly uniform cloud field between heights of approximately 750 and 2250 m across the extent of the domain for both winter and summer. This cloud field makes a transition from consisting primarily of liquid water at the lower latitudes to ice water at the higher latitudes. This transition is primarily driven by the gradient in the temperature, which is commonly between 0° and −20°C, rather than by direct physical observation. The uniform lower boundary is a consequence of the CloudSat cloud detection algorithm being unable to reliably separate radar returns because of the bright surface versus returns due to clouds, in the lowest four range bins above the surface. This is potentially very problematic over the Southern Ocean where the depth of the boundary layer has been observed to be as shallow as 500 m. Cloud fields inferred from upper-air soundings at Macquarie Island (54.62°S, 158.85°E) similarly suggest that the peak frequency lies between 260 and 500 m for both summer and winter. No immediate explanation is available for the uniformity of the cloud-top boundary. This lack of a strong seasonal cycle is, perhaps, remarkable given the large seasonal cycles in both the shortwave (SW) radiative forcing experienced and the cloud condensation nuclei (CCN) concentration over the Southern Ocean.
Shallow Convection and Precipitation Over the Southern Ocean: A Case Study During the CAPRICORN 2016 Field Campaign
Publisher: American Geophysical Union (AGU)
Date: 29-04-2021
DOI: 10.1029/2020JD034088
Abstract: Marine boundary layer clouds and precipitation observed in a sustained period of open mesoscale cellular convection (MCC) over the Southern Ocean (SO) are investigated using Clouds, Aerosols, Precipitation, Radiation, and atmospherIc Composition Over the southeRn oceaN 2016 observations, Himawari‐8 products, and numerical simulations. The shallow convection was characterized by the presence of supercooled liquid water and mixed‐phase clouds in the sub‐freezing temperature range, consistent with earlier in‐situ observations where ice multiplication is found to be active in producing large quantities of ice in open MCC clouds. Ice‐phase precipitation was observed to melt below cloud base with evidence of cold pools produced in a decoupled boundary layer. Convection‐permitting simulations using the weather research and forecasting model were able to reproduce many of the surface meteorological features and their evolution. However, the evolution of the boundary layer height and the degree of decoupling were poorly simulated, along with the absence of cold pools. The observed cloud morphology and microphysical characteristics were also not well reproduced in the control simulation with the Thompson microphysics scheme, where too much supercooled water was simulated in a too homogenous cloud field. Sensitivity experiments with modified microphysical parameters led to a higher production of glaciated clouds and precipitation. Sensitivity experiments with different boundary layer schemes and vertical resolution, however, showed a smaller impact. A bias of ∼4°C in the initial boundary conditions of the sea surface temperature is discussed. This study highlights the challenge of representing the complex physical processes that underpin the cloud, precipitation, and boundary layer characteristics of the open MCC over the SO.
A Modeling Case Study of Mixed-Phase Clouds over the Southern Ocean and Tasmania
Publisher: American Meteorological Society
Date: 03-2010
Abstract: The cloud structure associated with two frontal passages over the Southern Ocean and Tasmania is investigated. The first event, during August 2006, is characterized by large quantities of supercooled liquid water and little ice. The second case, during October 2007, is more mixed phase. The Weather Research and Forecasting model (WRFV2.2.1) is evaluated using remote sensed and in situ observations within the post frontal air mass. The Thompson microphysics module is used to describe in-cloud processes, where ice is initiated using the Cooper parameterization at temperatures lower than −8°C or at ice supersaturations greater than 8%. The evaluated cases are then used to numerically investigate the prevalence of supercooled and mixed-phase clouds over Tasmania and the ocean to the west. The simulations produce marine stratocumulus-like clouds with maximum heights of between 3 and 5 km. These are capped by weak temperature and strong moisture inversions. When the inversion is at temperatures warmer than −10°C, WRF produces widespread supercooled cloud fields with little glaciation. This is consistent with the limited in situ observations. When the inversion is at higher altitudes, allowing cooler cloud tops, glaciated (and to a lesser extent mixed phase) clouds are more common. The simulations are further explored to evaluate any orographic signature within the cloud structure over Tasmania. No consistent signature is found between the two cases.
Variations in Precipitation across the Southern Ocean
Publisher: American Meteorological Society
Date: 15-12-2020
Abstract: The Southern Ocean lies beneath a unique region of the global atmosphere with minimal effects of landmasses on the zonal flow. The absence of landmasses also means that in situ observations of precipitation are limited to a few ocean islands. Two reanalyses and two satellite-based gridded datasets are analyzed to estimate the character of the distribution of precipitation across the region. The latitudinal variation is computed across three longitudinal sectors, representing the Pacific, Atlantic, and Indian Oceans. The most recent ECMWF reanalysis (ERA5) is found to produce the most accurate estimate of the mean profile and seasonal cycle of precipitation. However, there is little consistency in the estimates of trends in monthly anomalies of precipitation. A more consistent description of precipitation trends is found by using linear regression of the precipitation anomaly with the local mean sea level pressure anomaly, the southern annular mode, and the Southern Oscillation index. In broad terms, precipitation is found to be decreasing at lower latitudes and increasing at higher latitudes, which is consistent with earlier climate model simulations on the impacts of anthropogenic climate change.
Characteristics of marine atmospheric boundary layer over the Southern Ocean in response to the synoptic forcing
Publisher: American Geophysical Union (AGU)
Date: 03-08-2018
DOI: 10.1029/2018JD028700
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