Claire Vincent

Characterization of aerosols over the Great Barrier Reef: The influence of transported continental sources

Publisher: Elsevier BV

Date: 11-2019

DOI: 10.1016/J.SCITOTENV.2019.07.007

Abstract: The rapid environmental changes in Australia prompt a more thorough investigation of the influence of transportation, local emissions, and optical-chemical properties on aerosol production across the region. A month-long intensive measurement c aign was conducted during spring 2016 at Mission Beach, a remote coastal site west of the Great Barrier Reef (GBR) on the north-east coast of Australia. One aerosol pollution episode was investigated in early October. This event was governed by meteorological conditions and characterized by the increase in black carbon (BC) mass concentration (averaged value of 0.35 ± 0.20 μg m

Diurnal Cycle of Surface Winds in the Maritime Continent Observed through Satellite Scatterometry

Publisher: American Meteorological Society

Date: 06-2019

DOI: 10.1175/MWR-D-18-0433.1

Abstract: The diurnal cycle of surface winds throughout the Maritime Continent plays a significant role in the formation of precipitation over the islands of the region and over the surrounding seas. This study investigates the connection between the diurnal cycles of surface wind and offshore precipitation using data from four satellite scatterometer instruments and two satellite precipitation radar instruments. For the first time, data from three scatterometer instruments are combined to yield a more temporally complete picture of the surface wind diurnal cycles over the Maritime Continent’s surrounding seas. The results indicate that land–sea breezes typically propagate over 400 km offshore, produce mean wind perturbations of between 1 and 5 m s −1 , and propagate as gravity waves at 25–30 m s −1 . Diurnal precipitation cycles are affected through gravity wave propagation processes associated with the land–sea breezes, and through the convergence of land breezes from nearby islands. These observational results are then compared with previous mesoscale modeling results. It is shown that land–sea breezes occur too early, and are too intense in these modeling results, and this may partly explain why these modeling results also exhibit an early, overly intense diurnal precipitation cycle. This study also investigates variations in the diurnal cycle of surface winds at seasonal and intraseasonal time scales. Previous work has suggested that seasonal and intraseasonal variations in surface heating affect the land–sea breeze circulation and diurnal precipitation cycles we argue that variations in background winds also play a defining role in modulating coastally influenced local winds.

Locally forced convection in subkilometre‐scale simulations with the Unified Model and WRF

Publisher: Wiley

Date: 16-08-2020

DOI: 10.1002/QJ.3855

Abstract: This study evaluates the performance and benefits of kilometre‐ and subkilometre‐scale convection‐permitting simulations over tropical Australia. Focusing on an extended monsoon break period, we can directly compare Unified Model (UM) and Weather Research and Forecasting model (WRF) simulations to C‐band polarimetric radar observations and soundings. We show that the two models have different behaviour, and both are different to observations. Whereas WRF produces daily squall lines whether or not they occurred in observations, the UM primarily generates small but intense storms. The UM and WRF produce qualitatively different surface density currents at different times in the diurnal cycle. Once the density currents are present, the models also show different behaviour in relation to convective initiation. While higher resolution helps in the distribution of total precipitation over the domain, most characteristics do not change with higher resolutions, and model differences are always larger than resolution differences. While Convective Available Potential Energy/Convective Inhibition (CAPE/CIN) does not seem to be important to explain model differences, our findings point to the evolution of density currents in the boundary layer as the most important source of model errors and differences.

Using Global and Regional Model Simulations to Understand Maritime Continent Wet‐Season Rainfall Variability

Publisher: American Geophysical Union (AGU)

Date: 28-11-2018

DOI: 10.1029/2018GL080201

Multiscale Influences on Rainfall in Northeast Australia

Publisher: American Meteorological Society

Date: 09-2023

DOI: 10.1175/JCLI-D-22-0835.1

Abstract: This study examines the multiscale modulation of mean and extreme rainfall in Northeast (NE) Australia under different background modes of variability, which is a new aspect given the high-resolution and long-term observational datasets. Daily rainfall probability is significantly modified by the Madden–Julian oscillation (MJO), and its influence varies with the seasons and is associated with atmospheric circulation anomalies. Rainfall generally decreases during El Niño and increases during La Niña years however, there is a notable spatial nuance to El Niño–Southern Oscillation (ENSO)-associated extreme rainfall, with some locations showing the opposite precipitation response to the typical ENSO–rainfall relationship. Despite more precipitation overall in La Niña years, the mean and extreme precipitation responses to the MJO appear to be stronger and more often statistically significant during El Niño compared to La Niña periods. The impact of ENSO on the MJO–rainfall relationship is stronger than the variation of the MJO itself with ENSO, and likely reflects a change in the MJO modulation of rain-bearing atmospheric processes. During El Niño periods, diurnal rainfall litude is generally stronger in the central and southern subtropical parts of the study area than during La Niña periods, while the opposite tendency occurs in the northern tropical part. The diurnal cycle of both mean and extreme precipitation is lified during suppressed convection phases compared to enhanced convection phases of the MJO. In general, the peak time of diurnal cycle does not change with MJO regimes, but there are some notable differences in rainfall propagation between enhanced and suppressed MJO phases. This study presents a new perspective on the relationship between precipitation in Northeast (NE) Australia and two important climate modes, the Madden–Julian oscillation (MJO) and El Niño–Southern Oscillation (ENSO). Rainfall in NE Australia is strongly influenced by the MJO, ENSO, and their interaction, suggesting that climate models need to capture both in idual climate modes and their interactions for reliable rainfall projections. These findings have societal climate risk implications, as NE Australia is an area prone to catastrophic flooding due to extreme rainfall.

A 10-Year Austral Summer Climatology of Observed and Modeled Intraseasonal, Mesoscale, and Diurnal Variations over the Maritime Continent

Publisher: American Meteorological Society

Date: 05-2017

DOI: 10.1175/JCLI-D-16-0688.1

Abstract: The Maritime Continent is one of the wettest regions on the planet and has been shown to be important for global budgets of heat and moisture. Convection in the region, however, varies on several interrelated scales, making it difficult to quantify the precipitation climate and understand the key processes. For ex le, the diurnal cycle in precipitation over the land varies substantially according to the phase of the Madden–Julian oscillation (MJO), and the diurnal precipitation cycle over the water is coupled to that over the land, in some cases for distances of over 1000 km from the coast. Here, a 10-yr austral summer climatology of diurnal and MJO-scale variations in rain rate over the land and sea over the Maritime Continent is presented. The climatology is based on mesoscale model simulations with a horizontal grid length of 4 km and satellite precipitation estimates. The litude of the observed diurnal precipitation cycle is shown to reach a maximum just prior to the MJO active phase, with a weaker secondary maximum after the MJO active phase. Although these two maxima also exist in the modeled diurnal precipitation cycle, there is less difference between the maxima before and after the MJO active phase than in the observations. The modeled sea-breeze circulation is also shown to possess approximately equal maxima just before and just after the MJO active period, suggesting that the asymmetry of the diurnal precipitation cycle about the MJO active period is related more to moisture availability than kinematic forcing.

Meso‐ and microscale response to variation in cloudiness at three forested sites in the Maritime Continent

Publisher: Wiley

Date: 17-12-2021

DOI: 10.1002/QJ.4212

Abstract: This study examines the relationships between the diurnal precipitation cycle, local morning insolation, and local and large‐scale moisture availability using local radiative flux and precipitation observations from three forested tropical sites, together with ERA5 reanalysis data. Our results suggest that, away from the coast, there is a weak positive correlation between local morning insolation and the magnitude of the afternoon precipitation peak, and a weak negative relationship between locally observed surface moisture in the morning and the magnitude of the afternoon precipitation peak. There is little relationship between large‐scale column moisture and the local afternoon precipitation peak. We examine analogous results in convection‐permitting simulations. Results suggest that the simulated afternoon precipitation rate shows almost no dependence on surface radiative forcing or moisture availability, while the observed afternoon precipitation rate is dominated by radiative forcing. Simulated and observed satellite precipitation and cloud estimates for a single case study suggest a ersity of surface‐flux–precipitation relationships amongst model configurations.

3-D Tomographic Reconstruction of Rain Field Using Microwave Signals From LEO Satellites: Principle and Simulation Results

Publisher: Institute of Electrical and Electronics Engineers (IEEE)

Date: 08-2019

DOI: 10.1109/TGRS.2019.2899391

Scatterometer estimates of the tropical sea‐breeze circulation near Darwin, with comparison to regional models

Publisher: Wiley

Date: 10-2017

DOI: 10.1002/QJ.3131

The Australian Northwest Cloudband: Climatology, Mechanisms, and Association with Precipitation

Publisher: American Meteorological Society

Date: 10-09-2019

DOI: 10.1175/JCLI-D-19-0031.1

Abstract: Australian northwest cloudbands (NWCBs) are continental-scale bands of continuous cloud that stretch from northwest to southeast Australia. In earlier studies, where the characteristics of NWCBs and their relationship with precipitation were identified from satellite imagery, there was considerable uncertainty in the results due to limited quality and availability of data. The present study identifies NWCBs from 31 years of satellite data using a pattern-matching algorithm. This new climatology is the longest record based entirely on observations. Our findings include a strong annual cycle in NWCB frequency, with a summer maximum and winter minimum, and a statistically significant increase in annual NWCB days over the period 1984–2014. Physical mechanisms responsible for NWCB occurrences are explored to determine whether there is a fundamental difference between summer and winter NWCBs as hypothesized in earlier studies. Composite analyses are used to reveal that a key difference between these is their genesis mechanisms. Whereas summer NWCBs are triggered by cyclonic disturbances, winter NWCBs tend to form when meridional sea surface temperature gradients trigger baroclinic instability. It was also found that while precipitation is enhanced over parts of Australia during a cloudband day, it is reduced in other regions. During a cloudband day, precipitation extremes are more likely over northwest, central, and southeast Australia, while the probability of extreme precipitation decreases in northeast and southwest Australia. Additionally, cold fronts and NWCBs can interact, leading to enhanced rainfall over Australia.

The diurnal cycle of rainfall and cloud properties from Himawari-8 during the austral summer (2016-2020).

Publisher: Wiley

Date: 14-12-2021

DOI: 10.1002/ESSOAR.10509504.1

A Case Study of a West Sumatra Squall Line Using Satellite Observations

Publisher: American Meteorological Society

Date: 02-2023

DOI: 10.1175/MWR-D-21-0194.1

Abstract: A West Sumatra squall line occurred on 10 January 2016, with a clear offshore propagation of convection. Satellite-derived products from Himawari-8 Advanced Himawari Imager and the Geostationary Cloud Algorithm Testbed Geocat are used to investigate the westward propagation of cloudiness from Sumatra to the Indian Ocean with a lifetime of 1.5 days. A convective mask based on deep convective cell detection and a cell-tracking algorithm are used to estimate the propagation speed of the cloud system. Two distinct mesoscale convective responses are identified: 1) a rapid development in South Sumatra is influenced by the convective environment over the Indian Ocean. The propagation speed is estimated to be ∼5 m s −1 within the first 200 km from the coast. This speed is consistent with density currents. In contrast, 2) the coupling to the inertia–gravity wave is only evident for the northwest of Sumatra with speeds of ∼12 m s −1 . The analysis of brightness temperature from the 10.4- μ m spectral band and cloud-top temperature showed that the lifetime of the squall line is approximately 30 h with a propagating distance of ∼1000 km. Retrieved cloud properties and tracking of the offshore propagation indicated that the cloud structure consisted of multiple types of cells, propagating as envelopes of convection, and revealed the influence of large-scale variability of the Indian Ocean. Filtered OLR anomalies, satellite-derived rainfall, moisture flux convergence, and background winds flow around Sumatra are used to explore the effects of Kelvin wave activity that likely influenced the lifetime of the squall line.

A local index of Maritime Continent intraseasonal variability based on rain rates over the land and sea

Publisher: American Geophysical Union (AGU)

Date: 10-09-2016

DOI: 10.1002/2016GL069987

Mesoscale Variation in Diabatic Heating around Sumatra, and Its Modulation with the Madden–Julian Oscillation

Publisher: American Meteorological Society

Date: 26-07-2018

DOI: 10.1175/MWR-D-17-0392.1

Abstract: Diabatic heating in the Maritime Continent region is controlled by a unique blend of mesoscale variability associated with steep topography and complex coastlines and intraseasonal variability associated with propagating planetary-scale disturbances. In this study, the diabatic heating from a 10-yr austral summer simulation over the Maritime Continent with a 4-km horizontal grid length is analyzed with respect to diurnal, spatial, and intraseasonal variations. Results are compared, where possible, to analogous estimates from the TRMM precipitation radar. We show that the heating budget is largely a balance between latent heating and vertical advection, with rays of heating and cooling extending upward and outward from the coast evident in the advection terms, consistent with the gravity wave representation of the tropical sea breeze. By classifying rainfall into convective and stratiform components, it is shown that simulated convective heating over Sumatra peaks in MJO phases 2 and 3, while simulated stratiform heating peaks in phase 4. Similarly, spectral latent heating estimates from the TRMM Precipitation Radar show that stratiform heating peaks in phases 3 and 4, while convective heating peaks in phases 2 and 3. It is also shown that stratiform precipitation plays a greater role in offshore precipitation during the night, albeit with embedded convective cores, than over the land during the day. These results emphasize the importance of achieving a realistic representation of convective and stratiform processes in high-resolution simulations in the tropics, both for total rainfall estimates and for realistic latent heating.

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE200100040

Start Date: 04-2020

End Date: 07-2021

Amount: $580,000.00

Funder: Australian Research Council

ARC Centres Of Excellence - Grant ID: CE230100012

Start Date: 02-2024

End Date: 01-2030

Amount: $35,000,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP230100639

Start Date: 2023

End Date: 12-2025

Amount: $378,000.00

Funder: Australian Research Council

ARC Centres Of Excellence - Grant ID: CE170100023

Start Date: 08-2017

End Date: 12-2024

Amount: $30,050,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP190100786

Start Date: 02-2019

End Date: 04-2023

Amount: $465,000.00

Funder: Australian Research Council