ORCID Profile
0000-0002-4378-2263
Current Organisation
Australian Bureau of Meteorology
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Publisher: Springer Science and Business Media LLC
Date: 26-05-2017
DOI: 10.1038/S41598-017-02688-Y
Abstract: Episodic anomalously warm sea surface temperature (SST) extremes, or marine heatwaves (MHWs), lify ocean warming effects and may lead to severe impacts on marine ecosystems. MHW-induced coral bleaching events have been observed frequently in recent decades in the southeast Indian Ocean (SEIO), a region traditionally regarded to have resilience to global warming. In this study, we assess the contribution of El Niño-Southern Oscillation (ENSO) to MHWs across the mostly understudied reefs in the SEIO. We find that in extended summer months, the MHWs at tropical and subtropical reefs ( ided at ~20°S) are driven by opposite ENSO polarities: MHWs are more likely to occur at the tropical reefs during eastern Pacific El Niño, driven by enhanced solar radiation and weaker Australian Monsoon, some likely alleviated by positive Indian Ocean Dipole events, and at the subtropical reefs during central Pacific La Niña, mainly caused by increased horizontal heat transport, and in some cases reinforced by local air-sea interactions. Madden-Julian Oscillations (MJO) also modulate the MHW occurrences. Projected future increases in ENSO and MJO intensity with greenhouse warming will enhance thermal stress across the SEIO. Implementing forecasting systems of MHWs can be used to anticipate future coral bleaching patterns and prepare management responses.
Publisher: American Meteorological Society
Date: 09-2010
Publisher: American Meteorological Society
Date: 03-2019
Abstract: El Niño and La Niña, the warm and cold phases of El Niño–Southern Oscillation (ENSO), cause significant year-to-year disruptions in global climate, including in the atmosphere, oceans, and cryosphere. Australia is one of the countries where its climate, including droughts and flooding rains, is highly sensitive to the temporal and spatial variations of ENSO. The dramatic impacts of ENSO on the environment, society, health, and economies worldwide make the application of reliable ENSO predictions a powerful way to manage risks and resources. An improved understanding of ENSO dynamics in a changing climate has the potential to lead to more accurate and reliable ENSO predictions by facilitating improved forecast systems. This motivated an Australian national workshop on ENSO dynamics and prediction that was held in Sydney, Australia, in November 2017. This workshop followed the aftermath of the 2015/16 extreme El Niño, which exhibited different characteristics to previous extreme El Niños and whose early evolution since 2014 was challenging to predict. This essay summarizes the collective workshop perspective on recent progress and challenges in understanding ENSO dynamics and predictability and improving forecast systems. While this essay discusses key issues from an Australian perspective, many of the same issues are important for other ENSO-affected countries and for the international ENSO research community.
Publisher: American Meteorological Society
Date: 02-2013
Abstract: Seasonal rainfall predictions for Australia from the Predictive Ocean Atmosphere Model for Australia (POAMA), version P15b, coupled model seasonal forecast system, which has been run operationally at the Australian Bureau of Meteorology since 2002, are overconfident (too low spread) and only moderately reliable even when forecast accuracy is highest in the austral spring season. The lack of reliability is a major impediment to operational uptake of the coupled model forecasts. Considerable progress has been made to reduce reliability errors with the new version of POAMA2, which makes use of a larger ensemble from three different versions of the model. Although POAMA2 can be considered to be multimodel, its in idual models and forecasts are similar as a result of using the same perturbed initial conditions and the same model lineage. Reliability of the POAMA2 forecasts, although improved, remains relatively low. Hence, the authors explore the additional benefit that can be attained using more independent models available in the European Union Ensemble-Based Predictions of Climate Changes and their Impacts (ENSEMBLES) project. Although forecast skill and reliability of seasonal predictions of Australian rainfall are similar for POAMA2 and the ENSEMBLES models, forming a multimodel ensemble using POAMA2 and the ENSEMBLES models is shown to markedly improve reliability of Australian seasonal rainfall forecasts. The benefit of including POAMA2 into this multimodel ensemble is due to the additional information and skill of the independent model, and not just due to an increase in the number of ensemble members. The increased reliability, as well as improved accuracy, of regional rainfall forecasts from this multimodel ensemble system suggests it could be a useful operational prediction system.
Publisher: American Meteorological Society
Date: 1998
Publisher: American Meteorological Society
Date: 10-1998
Publisher: Elsevier BV
Date: 05-2004
Publisher: American Meteorological Society
Date: 09-2011
Abstract: No Abstract available.
Publisher: American Geophysical Union (AGU)
Date: 21-08-2020
DOI: 10.1029/2020JD032952
Abstract: The Southern Hemisphere experienced its first recorded major sudden stratospheric warming during September 2002, which subsequently resulted in strong low polarity of the Southern Annular Mode (low SAM) and extreme daily mean maximum temperatures and low rainfall over eastern Australia during October 2002. The warming and weakening of the polar vortex were accompanied by anomalously high values of polar stratospheric ozone, which possibly could have constructively sustained the weakened vortex and subsequent development of low SAM. We explore the impact of this ozone variation by conducting an idealized forecast experiment using the Australian Bureau of Meteorology's operational subseasonal to seasonal prediction system (Australian Community Climate and Earth System Simulator‐Seasonal forecast system version 1, ACCESS‐S1), whose atmospheric model well resolves the stratosphere. The ACCESS‐S1 control forecasts are generated with prescribed climatological monthly mean ozone, whereas the observed monthly mean ozone during 2002 is prescribed during the forecast for the experiment. While the control forecasts initialized on 1 August 2002 demonstrate good skill in predicting the weakening of the polar vortex and the resultant occurrence of low SAM during October, the extremity of the SAM anomaly and associated extreme high temperatures and low rainfall over eastern Australia were significantly underpredicted. Prescribing the observed ozone results in more realistic weakening of the stratospheric vortex and stronger development of low SAM and extreme warm conditions in eastern Australia during October 2002. These results suggest that polar stratospheric ozone variations are a potential source of long lead climate variability, which can be tapped with future ACCESS‐S development.
Publisher: Springer Science and Business Media LLC
Date: 22-02-2014
Publisher: Springer Science and Business Media LLC
Date: 22-06-2018
Publisher: Springer Science and Business Media LLC
Date: 05-05-2006
Publisher: American Meteorological Society
Date: 07-1998
Publisher: Elsevier BV
Date: 12-2015
Publisher: American Meteorological Society
Date: 07-03-2016
Abstract: Interannual variations of upper-ocean salinity in the tropical Pacific and relationships with ENSO are investigated using the Bureau of Meteorology (Australia) POAMA Ensemble Ocean Data Assimilation System (PEODAS) reanalyses. Empirical orthogonal function (EOF) analysis reveals the systematic evolution of salinity and temperature during ENSO. EOF1 and EOF2 of both temperature and salinity capture the mature phase of El Niño and the discharge and recharge phase, respectively. Typical El Niño and La Niña evolution captured by the leading pair of EOFs depicts eastward or westward migration of the eastern edge of the warm/fresh pool in the western Pacific. Increased or decreased freshness in the western Pacific mixed layer occurs in the recharge/discharge phase. EOF3 captures extreme El Niño, when the strong positive temperature anomaly extends to the South American coast and the fresh pool detaches from the western Pacific and shifts into the central Pacific. Large loadings on EOF3 occurred only during 1982/83 and 1997/98, which suggests that eastern Pacific El Niño is actually the exception, whereas moderate central Pacific El Niño and La Niña are more typical. The eastward expansion of the warm/fresh pool during El Niño is also associated with a continuous eastward displacement of the barrier layer, indicating an active role of the barrier layer not just at the onset of an event. The barrier layer and fresh pool shift much farther eastward during strong El Niño, which could contribute to the eastward shift of strong events. The prior enhancement of the barrier layer in the western Pacific is also more concentrated and stronger, which might portend development of extreme El Niño.
Publisher: Springer Science and Business Media LLC
Date: 19-11-2019
DOI: 10.1038/S41598-019-53371-3
Abstract: Observational records show that occurrences of the negative polarity of the Southern Annular Mode (low SAM) is significantly linked to El Niño during austral spring and summer, potentially providing long-lead predictability of the SAM and its associated surface climate conditions. In this study, we explore how this linkage may change under a scenario of a continuation of the ocean temperature trends that have been observed over the past 60 years, which are plausibly forced by increasing greenhouse gas concentrations. We generated coupled model seasonal forecasts for three recent extreme El Niño events by initialising the forecasts with observed ocean anomalies of 1 September 1982, 1997 and 2015 added into (1) the current ocean mean state and into (2) the ocean mean state updated to include double the recent ocean temperature trends. We show that the strength of extreme El Niño is reduced with the warmer ocean mean state as a result of reduced thermocline feedback and weakened rainfall-wind-sea surface temperature coupling over the tropical eastern Pacific. The El Niño-low SAM relationship also weakens, implying the possibility of reduced long-lead predictability of the SAM and associated surface climate impacts in the future.
Publisher: American Meteorological Society
Date: 06-1990
Publisher: American Meteorological Society
Date: 02-09-2016
Abstract: Predictive skill for El Niño in the equatorial eastern Pacific across a range of forecast models declined sharply in the early twenty-first century relative to what was achieved in the late twentieth century despite ongoing improvements of forecast systems. This decline coincided with a shift in Pacific climate to an enhanced east–west surface temperature gradient across the Pacific and a stronger Walker circulation at the end of the twentieth century. Using seasonal forecast sensitivity experiments with the Australian Bureau of Meteorology coupled model POAMA2.4, the authors show that this shift in background climate acted to weaken key ocean–atmosphere feedbacks that lify eastern Pacific El Niño, thus resulting in weaker variability that is less predictable. These results indicate that extreme El Niños, such as those that occurred in 1982/83 and 1997/98, were conditioned by the background climate and so were favored to occur in the late twentieth century. However, anticipating future changes in El Niño variability and predictability is an outstanding challenge because causes and prediction of low-frequency variations of Pacific climate have not yet been demonstrated.
Publisher: American Meteorological Society
Date: 04-2001
Publisher: Wiley
Date: 31-01-2015
DOI: 10.1002/QJ.2510
Publisher: American Geophysical Union (AGU)
Date: 04-12-2013
DOI: 10.1002/2013GL057731
Abstract: Southern Hemisphere (SH) climate change has been partly attributed to Antarctic ozone depletion in the literatures. Here we show that the ozone hole has affected not only the long‐term climate change but also the interannual variability of SH surface climate. A significant negative correlation is observed between September ozone concentration and the October southern annular mode index, resulting in systematic variations in precipitation and surface air temperature throughout the SH. This time‐lagged relationship is comparable to and independent of that associated with El Niño‐Southern Oscillation and the Indian Ocean Dipole Mode, suggesting that SH seasonal forecasts could be improved by considering Antarctic stratospheric variability.
Publisher: American Meteorological Society
Date: 15-05-2009
Abstract: The impact of stochastic intraseasonal variability on the onset of the 1997/98 El Niño was examined using a large ensemble of forecasts starting on 1 December 1996, produced using the Australian Bureau of Meteorology Predictive Ocean Atmosphere Model for Australia (POAMA) seasonal forecast coupled model. This coupled model has a reasonable simulation of El Niño and the Madden–Julian oscillation, so it provides an ideal framework for investigating the interaction between the MJO and El Niño. The experiment was designed so that the ensemble spread was simply a result of internal stochastic variability that is generated during the forecast. For the initial conditions used here, all forecasts led to warm El Niño–type conditions with the litude of the warming varying from 0.5° to 2.7°C in the Niño-3.4 region. All forecasts developed an MJO event during the first 4 months, indicating that perhaps the background state favored MJO development. However, the details of the MJOs that developed during December 1996–March 1997 had a significant impact on the subsequent strength of the El Niño event. In particular, the forecasts with the initial MJOs that extended farther into the central Pacific, on average, led to a stronger El Niño, with the westerly winds in the western Pacific associated with the MJO leading the development of SST and thermocline anomalies in the central and eastern Pacific. These results imply a limit to the accuracy with which the strength of El Niño can be predicted because the details of in idual MJO events matter. To represent realistic uncertainty, coupled models should be able to represent the MJO, including its propagation into the central Pacific so that forecasts produce sufficient ensemble spread.
Publisher: Wiley
Date: 10-2017
DOI: 10.1002/QJ.3166
Publisher: American Meteorological Society
Date: 2013
Abstract: The authors assess the sensitivity of the simulated mean state and coupled variability to systematic initial state salinity errors in seasonal forecasts using the Australian Bureau of Meteorology Predictive Ocean Atmosphere Model for Australia (POAMA) coupled model. This analysis is based on two sets of hindcasts that were initialized from old and new ocean initial conditions, respectively. The new ocean initial conditions are provided by an ensemble multivariate analysis system that assimilates subsurface temperatures and salinity and is a clear improvement over the previous system, which was based on univariate optimal interpolation, using static error covariances and assimilating only temperature without updating salinity. Large systematic errors in the salinity field around the thermocline region of the tropical western and central Pacific produced by the old assimilation scheme are shown to have strong impacts on the predicted mean state and variability in the tropical Pacific for the entire 9 months of the forecast. Forecasts initialized from the old scheme undergo a rapid and systematic adjustment of density that causes large persistent changes in temperature both locally in the western and central Pacific thermocline, but also remotely in the eastern Pacific via excitation of equatorial waves. The initial subsurface salinity errors in the western and central Pacific ultimately result in an altered surface climate because of induced temperature changes in the thermocline that trigger a coupled feedback in the eastern Pacific. These results highlight the importance of accurately representing salinity in initial conditions for climate prediction on seasonal and potentially multiyear time scales.
Publisher: American Meteorological Society
Date: 06-2003
Publisher: Springer Science and Business Media LLC
Date: 20-11-2022
Publisher: American Meteorological Society
Date: 1984
Publisher: American Geophysical Union (AGU)
Date: 12-2019
DOI: 10.1029/2019JC015458
Publisher: American Meteorological Society
Date: 02-2007
DOI: 10.1175/JCLI4003.1
Abstract: Observations of the development of recent El Niño events suggest a pivotal role for the Madden–Julian oscillation (MJO). Previous attempts to uncover a systematic relationship between MJO activity and the El Niño–Southern Oscillation (ENSO), however, have yielded conflicting results. In this study the MJO–ENSO relationship is stratified by season, and the focus is on MJO activity in the equatorial western Pacific. The results demonstrate that MJO activity in late boreal spring leads El Niño in the subsequent autumn–winter for the period 1979–2005. Spring is the season when MJO activity is least asymmetric with respect to the equator and displays the most sensitivity to SST variations at the eastern edge of the warm pool. Enhanced MJO activity in the western Pacific in spring is associated with an eastward-expanded warm pool and low-frequency westerly surface zonal wind anomalies. These sustained westerly anomalies in the western Pacific are hypothesized to project favorably onto a developing El Niño in spring.
Publisher: American Meteorological Society
Date: 2004
Publisher: Springer Science and Business Media LLC
Date: 19-02-2011
Publisher: Springer Science and Business Media LLC
Date: 14-04-2009
Publisher: Springer Science and Business Media LLC
Date: 23-09-2019
Publisher: American Meteorological Society
Date: 12-2015
Publisher: Springer Science and Business Media LLC
Date: 09-01-2014
Publisher: American Meteorological Society
Date: 06-2007
DOI: 10.1175/JCLI4134.1
Abstract: Daily variations in Australian rainfall and surface temperature associated with the Southern Hemisphere annular mode (SAM) are documented using observations for the period 1979–2005. The high index polarity of the SAM is characterized by a poleward contraction of the midlatitude westerlies. During winter, the high index polarity of the SAM is associated with decreased daily rainfall over southeast and southwest Australia, but during summer it is associated with increased daily rainfall on the southern east coast of Australia and decreased rainfall in western Tasmania. Variations in the SAM explain up to ∼15% of the weekly rainfall variance in these regions, which is comparable to the variance accounted for by the El Niño–Southern Oscillation, especially during winter. The most widespread temperature anomalies associated with the SAM occur during the spring and summer seasons, when the high index polarity of the SAM is associated with anomalously low maximum temperature over most of central/eastern subtropical Australia. The regions of decreased maximum temperature are also associated with increased rainfall. Implications for recent trends in Australian rainfall and temperature are discussed.
Publisher: American Meteorological Society
Date: 23-04-2014
DOI: 10.1175/JCLI-D-13-00550.1
Abstract: Seasonal variations of subtropical precipitation anomalies associated with the southern annular mode (SAM) are explored for the period 1979–2011. In all seasons, high-polarity SAM, which refers to a poleward-shifted eddy-driven westerly jet, results in increased precipitation in high latitudes and decreased precipitation in midlatitudes as a result of the concomitant poleward shift of the midlatitude storm track. In addition, during spring–autumn, high SAM also results in increased rainfall in the subtropics. This subtropical precipitation anomaly is absent during winter. This seasonal variation of the response of subtropical precipitation to the SAM is shown to be consistent with the seasonal variation of the eddy-induced ergent meridional circulation in the subtropics (strong in summer and weak in winter). The lack of an induced ergent meridional circulation in the subtropics during winter is attributed to the presence of the wintertime subtropical jet, which causes a broad latitudinal span of eddy momentum flux ergence due primarily to higher phase speed eddies breaking poleward of the subtropical jet and lower speed eddies not breaking until they reach the equatorward flank of the subtropical jet. During the other seasons, when the subtropical jet is less distinctive, the critical line for both high and low speed eddies is on the equatorward flank of the single jet and so breaking in the subtropics occurs over a narrow range of latitudes. The implications of these findings for the seasonality of future subtropical climate change, in which a shift to high SAM in all seasons is expected to be promoted, are discussed.
Publisher: American Geophysical Union (AGU)
Date: 25-08-2017
DOI: 10.1002/2017GL074244
Publisher: American Meteorological Society
Date: 12-2000
Publisher: American Geophysical Union (AGU)
Date: 07-08-2019
DOI: 10.1029/2019GL083152
Abstract: Seasonal activity of the Madden‐Julian Oscillation (MJO) is observed to be greater during austral summer when the lower stratospheric winds are in the easterly phase of the quasi‐biennial oscillation (QBO). Using initialized predictions from two coupled model seasonal prediction systems, we show a systematic impact of the QBO on the litude of the MJO during the first few days of the forecast before model biases become too large. In both models as for the observed, the difference in MJO litude between easterly phases and westerly phases of the QBO increases with lead time, despite having similar initial litudes. Enhanced destabilization of the tropopause is argued to be the key mechanism that promotes stronger MJO convection during easterly phase of QBO. Caveats for the inability of the models to reproduce the observed strength of the MJO‐QBO relationship are discussed.
Publisher: American Meteorological Society
Date: 10-2009
Abstract: This work identifies and documents a suite of large-scale drivers of rainfall variability in the Australian region. The key driver in terms of broad influence and impact on rainfall is the El Niño–Southern Oscillation (ENSO). ENSO is related to rainfall over much of the continent at different times, particularly in the north and east, with the regions of influence shifting with the seasons. The Indian Ocean dipole (IOD) is particularly important in the June–October period, which spans much of the wet season in the southwest and southeast where IOD has an influence. ENSO interacts with the IOD in this period such that their separate regions of influence cover the entire continent. Atmospheric blocking also becomes most important during this period and has an influence on rainfall across the southern half of the continent. The Madden–Julian oscillation can influence rainfall in different parts of the continent in different seasons, but its impact is strongest on the monsoonal rains in the north. The influence of the southern annular mode is mostly confined to the southwest and southeast of the continent. The patterns of rainfall relationship to each of the drivers exhibit substantial decadal variability, though the characteristic regions described above do not change markedly. The relationships between large-scale drivers and rainfall are robust to the selection of typical indices used to represent the drivers. In most regions the in idual drivers account for less than 20% of monthly rainfall variability, though the drivers relate to a predictable component of this variability. The amount of rainfall variance explained by in idual drivers is highest in eastern Australia and in spring, where it approaches 50% in association with ENSO and blocking.
Publisher: American Meteorological Society
Date: 09-1990
Publisher: Springer Science and Business Media LLC
Date: 02-01-2019
DOI: 10.1038/S41467-018-07689-7
Abstract: After exhibiting an upward trend since 1979, Antarctic sea ice extent (SIE) declined dramatically during austral spring 2016, reaching a record low by December 2016. Here we show that a combination of atmospheric and oceanic phenomena played primary roles for this decline. The anomalous atmospheric circulation was initially driven by record strength tropical convection over the Indian and western Pacific Oceans, which resulted in a wave-3 circulation pattern around Antarctica that acted to reduce SIE in the Indian Ocean, Ross and Bellingshausen Sea sectors. Subsequently, the polar stratospheric vortex weakened significantly, resulting in record weakening of the circumpolar surface westerlies that acted to decrease SIE in the Indian Ocean and Pacific Ocean sectors. These processes appear to reflect unusual internal atmosphere-ocean variability. However, the warming trend of the tropical Indian Ocean, which may partly stem from anthropogenic forcing, may have contributed to the severity of the 2016 SIE decline.
Publisher: American Meteorological Society
Date: 15-08-2007
DOI: 10.1175/JCLI4228.1
Abstract: Australia typically experiences drought during El Niño, especially across the eastern two-thirds of the continent during austral spring (September–November). There have, however, been some interesting departures from this paradigm. For instance, the near-record-strength El Niño of 1997 was associated with near-normal rainfall. In contrast, eastern Australia experienced near-record drought during the modest El Niño of 2002. This stark contrast raises the issue of how the magnitude of the drought is related to the character and magnitude of El Niño, for instance as measured by the broadscale sea surface temperature (SST) anomaly in the equatorial eastern Pacific. Internal (unpredictable) atmospheric noise is one plausible explanation for this contrasting behavior during these El Niño events. Here, the authors suggest that Australian rainfall is sensitive to the zonal distribution of SST anomalies during El Niño and, in particular, the greatest sensitivity is to the SST variations on the eastern edge of the Pacific warm pool rather than in the eastern Pacific where El Niño variations are typically largest. Positive SST anomalies maximized near the date line in 2002, but in 1997 maximum anomalies were shifted well into the eastern Pacific, where their influence on Australian rainfall appears to be less. These findings provide a plausible physical basis for the view that forecasting the strength of El Niño is not sufficient to accurately predict rainfall variations across Australia during El Niño.
Publisher: American Meteorological Society
Date: 13-08-2019
Abstract: The seasonal-mean variance of the Madden–Julian oscillation (MJO) in austral summer has recently been shown to be significantly (p & 5%) enhanced during easterly phases of the quasi-biennial oscillation (QBO). The impact is large, with the mean MJO variance increasing by ~50% compared to the QBO westerly phase. In contrast, we show using observed outgoing longwave radiation that seasonal variations for convectively coupled equatorial Kelvin, Rossby, and mixed Rossby–gravity waves are insensitive to the QBO. This insensitivity extends to all high-frequency (2–30-day period) and the non-MJO component of the intraseasonal (30–120-day period) convective variance. However, convectively coupled Kelvin wave variability shows a modest increase (~13%) that is marginally significant (p = 10%) during easterly phases of the QBO in austral autumn, when Kelvin wave activity is seasonally strongest along the equator. The mechanism of impact on the Kelvin wave appears to be similar to what has previously been argued for the MJO during austral summer. However, the more tilted and shallower vertical structure of the Kelvin waves suggests that they cannot tap into the extra destabilization at the tropopause provided by the easterly phase of the QBO as effectively as the MJO. Lack of impact on the convectively coupled Rossby and mixed Rossby–gravity waves is argued to stem from their horizontal structure that results in weaker ergent anomalies along the equator, where the QBO impact is greatest. Our results further emphasize that the MJO in austral summer is uniquely affected by the QBO.
Publisher: Springer Science and Business Media LLC
Date: 04-03-2014
Publisher: American Meteorological Society
Date: 06-2013
Abstract: The development of a dynamical model seasonal prediction service for island nations in the tropical South Pacific is described. The forecast model is the Australian Bureau of Meteorology's Predictive Ocean–Atmosphere Model for Australia (POAMA), a dynamical seasonal forecast system. Using a hindcast set for the period 1982–2006, POAMA is shown to provide skillful forecasts of El Niño and La Niña many months in advance and, because the model faithfully simulates the spatial and temporal variability of rainfall associated with displacements of the southern Pacific convergence zone (SPCZ) and ITCZ during La Niña and El Niño, it also provides good predictions of rainfall throughout the tropical Pacific region. The availability of seasonal forecasts from POAMA should be beneficial to Pacific island countries for the production of regional climate outlooks across the region.
Publisher: American Meteorological Society
Date: 03-2008
Abstract: Simulations using an atmospheric model forced with observed SST climatology and the same atmospheric model coupled to a slab-ocean model are used to investigate the role of air–sea interaction on the dynamics of the MJO. Slab-ocean coupling improved the MJO in Australia’s Bureau of Meteorology atmospheric model over the Indo-Pacific warm pool by reducing its period from 70–100 to 45–70 days, thereby showing better agreement with the 30–80-day observed oscillation. Air–sea coupling improves the MJO by increasing the moisture flux in the lower troposphere prior to the passage of active convection, which acts to promote convection and precipitation on the eastern flank of the main convective center. This process is triggered by an increase in surface evaporation over positive SST anomalies ahead of the MJO convection, which are driven by the enhanced shortwave radiation in the region of suppressed convection. This in turn generates enhanced convergence into the region, which supports evaporation–wind feedback in the presence of weak background westerly winds. A subsequent increase in low-level moisture convergence acts to further moisten the lower troposphere in advance of large-scale convection in a region of reduced atmospheric pressure. This destabilizing mechanism is referred to as enhanced moisture convergence–evaporation feedback (EMCEF) and is utilized to understand the role of air–sea coupling on the observed MJO. The EMCEF mechanism also reconciles traditionally opposing ideas on the roles of frictional wave–conditional instability of the second kind (CISK) and wind–evaporation feedback. These results support the idea that the MJO is primarily an atmospheric phenomenon, with air–sea interaction improving upon, but not critical for, its existence in the model.
Publisher: Springer Science and Business Media LLC
Date: 19-03-2019
Publisher: American Meteorological Society
Date: 07-1995
Publisher: American Geophysical Union (AGU)
Date: 13-09-2011
DOI: 10.1029/2010WR009834
Publisher: Springer Science and Business Media LLC
Date: 22-01-2015
Publisher: American Meteorological Society
Date: 05-1999
Publisher: American Meteorological Society
Date: 10-07-2014
DOI: 10.1175/JCLI-D-13-00497.1
Abstract: Process-oriented diagnostics for Madden–Julian oscillation (MJO) simulations are being developed to facilitate improvements in the representation of the MJO in weather and climate models. These process-oriented diagnostics are intended to provide insights into how parameterizations of physical processes in climate models should be improved for a better MJO simulation. This paper proposes one such process-oriented diagnostic, which is designed to represent sensitivity of simulated convection to environmental moisture: composites of a relative humidity (RH) profile based on precipitation percentiles. The ability of the RH composite diagnostic to represent the ersity of MJO simulation skill is demonstrated using a group of climate model simulations participating in phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). A set of scalar process metrics that captures the key physical attributes of the RH diagnostic is derived and their statistical relationship with indices that quantify the fidelity of the MJO simulation is tested. It is found that a process metric that represents the amount of lower-tropospheric humidity increase required for a transition from weak to strong rain regimes has a robust statistical relationship with MJO simulation skill. The results herein suggest that moisture sensitivity of convection is closely related to a GCM’s ability to simulate the MJO.
Publisher: Springer Science and Business Media LLC
Date: 07-10-2019
Publisher: Frontiers Media SA
Date: 08-08-2019
Publisher: American Meteorological Society
Date: 04-2009
Abstract: The ocean dynamics of the Madden–Julian oscillation (MJO) and its interaction with El Niño–Southern Oscillation (ENSO) are assessed using a flux-corrected coupled model experiment from the Australian Bureau of Meteorology. The model demonstrates the correct oceanic Kelvin wave response to the MJO-related westerly winds in the western Pacific. Although there may be a role for the MJO in influencing the strength of El Niño, its impact is difficult to separate from that of strong heat content preconditioning of ENSO. Hence, the MJO–ENSO relationship is assessed starting from a background state of low heat content anomalies in the western Pacific that are also characteristic of recent observed El Niño events. The model shows a strong relationship between ENSO and the MJO near the peak of El Niño. At this time, the sea surface temperature (SST) anomaly is largest in the central Pacific, and it is difficult to separate cause and effect. Near the onset of El Niño, however, when Pacific Ocean SST anomalies are near zero, an increase in MJO activity is associated with Kelvin wave activity and stronger subsequent ENSO warming. A significant increase in the number of MJO events, rather than the strength of in idual MJO events, leads to stronger eastern Pacific warming the MJO appears not to be responsible for the occurrence of El Niño itself, but, rather, is important for influencing its development thus. This research supports a role for downwelling oceanic Kelvin waves and subsequent deepening of the thermocline in contributing to eastern Pacific warming during the onset of El Niño.
Publisher: Springer Science and Business Media LLC
Date: 26-04-2012
Publisher: American Meteorological Society
Date: 03-2013
Abstract: Seasonal predictions based on coupled atmosphere–ocean general circulation models (GCMs) provide useful predictions of large-scale circulation but lack the conditioning on topography required for locally relevant prediction. In this study a statistical downscaling model based on meteorological analogs was applied to continental-scale GCM-based seasonal forecasts and high quality historical site observations to generate a set of downscaled precipitation hindcasts at 160 sites in the South Murray Darling Basin region of Australia. Large-scale fields from the Predictive Ocean–Atmosphere Model for Australia (POAMA) 1.5b GCM-based seasonal prediction system are used for analog selection. Correlation analysis indicates modest levels of predictability in the target region for the selected predictor fields. A single best-match analog was found using model sea level pressure, meridional wind, and rainfall fields, with the procedure applied to 3-month-long reforecasts, initialized on the first day of each month from 1980 to 2006, for each model day of 10 ensemble members. Assessment of the total accumulated rainfall and number of rainy days in the 3-month reforecasts shows that the downscaling procedure corrects the local climate variability with no mean effect on predictive skill, resulting in a smaller magnitude error. The amount of total rainfall and number of rain days in the downscaled output is significantly improved over the direct GCM output as measured by the difference in median and tercile thresholds between station observations and downscaled rainfall. Confidence in the downscaled output is enhanced by strong consistency between the large-scale mean of the downscaled and direct GCM precipitation.
Publisher: American Meteorological Society
Date: 15-05-2005
DOI: 10.1175/JCLI3332.1
Abstract: Coupled ocean–atmosphere variability in the tropical Indian Ocean is explored with a multicentury integration of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Mark 3 climate model, which runs without flux adjustment. Despite the presence of some common deficiencies in this type of coupled model, zonal dipolelike variability is produced. During July through November, the dominant mode of variability of sea surface temperature resembles the observed zonal dipole and has out-of-phase rainfall variations across the Indian Ocean basin, which are as large as those associated with the model El Niño–Southern Oscillation (ENSO). In the positive dipole phase, cold SST anomaly and suppressed rainfall south of the equator on the Sumatra–Java coast drives an anticyclonic circulation anomaly that is consistent with the steady response (Gill model) to a heat sink displaced south of the equator. The northwest–southeast tilting Sumatra–Java coast results in cold sea surface temperature (SST) centered south of the equator, which forces anticylonic winds that are southeasterly along the coast, which thus produces local upwelling, cool SSTs, and promotes more anticylonic winds on the equator, the easterlies raise the thermocline to the east via upwelling Kelvin waves and deepen the off-equatorial thermocline to the west via off-equatorial downwelling Rossby waves. The model dipole mode exhibits little contemporaneous relationship with the model ENSO however, this does not imply that it is independent of ENSO. The model dipole often (but not always) develops in the year following El Niño. It is triggered by an unrealistic transmission of the model’s ENSO discharge phase through the Indonesian passages. In the model, the ENSO discharge Rossby waves arrive at the Sumatra–Java coast some 6 to 9 months after an El Niño peaks, causing the majority of model dipole events to peak in the year after an ENSO warm event. In the observed ENSO discharge, Rossby waves arrive at the Australian northwest coast. Thus the model Indian Ocean dipolelike variability is triggered by an unrealistic mechanism. The result highlights the importance of properly representing the transmission of Pacific Rossby waves and Indonesian throughflow in the complex topography of the Indonesian region in coupled climate models.
Publisher: American Meteorological Society
Date: 10-1991
Publisher: American Meteorological Society
Date: 06-2005
DOI: 10.1175/JCLI3374.1
Abstract: To shed light onto the possible role of stochastic forcing of the El Niño–Southern Oscillation (ENSO), the characteristics of observed tropical atmospheric variability that is statistically uncoupled from slowly evolving sea surface temperature (SST) are diagnosed. The Madden–Julian oscillation (MJO) is shown to be the dominant mode of variability within these uncoupled or “stochastic” components. The dominance of the MJO is important because the MJO generates oceanic Kelvin waves and perturbs SST in the equatorial Pacific that may feed back onto the El Niño–Southern Oscillation. The seasonality present in the uncoupled zonal stress (maximum in austral summer), which reflects the seasonality of MJO activity, is also transmitted to the eastern Pacific thermocline variability by these Kelvin waves. Hence, the MJO component of the uncoupled stress could plausibly contribute to the observed phase locking of ENSO to the seasonal cycle. During an El Niño event, maximum uncoupled zonal stress variance shifts eastward from the western Pacific along with the coupled surface westerly wind and warm SST anomalies. The MJO accounts for less than half of this low-frequency behavior of the uncoupled stress but accounts for nearly two-thirds of the resultant thermocline variability. The uncoupled zonal stress also exhibits weak, westerly anomalies in the western Pacific some 8–10 months prior to El Niño, which is mostly accounted for by the low-frequency (period ≫ 50 days) behavior of the MJO. This low-frequency behavior possibly explains why observed El Niño variability is recovered when weakly d ed models are forced with similar estimates of observed stochastic zonal stress.
Publisher: American Geophysical Union (AGU)
Date: 20-04-1994
DOI: 10.1029/94JD00045
Publisher: Springer Science and Business Media LLC
Date: 23-05-2017
DOI: 10.1038/S41598-017-01479-9
Abstract: Multi-year La Niña events often induce persistent cool and wet climate over global lands, altering and in some case mitigating regional climate warming impacts. The latest event lingered from mid-2010 to early 2012 and brought about intensive precipitation over many land regions of the world, particularly Australia. This resulted in a significant drop in global mean sea level despite the background upwards trend. This La Niña event is surprisingly predicted out to two years ahead in a few coupled models, even though the predictability of El Niño-Southern Oscillation during 2002–2014 has declined owing to weakened ocean-atmosphere interactions. However, the underlying mechanism for high predictability of this multi-year La Niña episode is still unclear. Experiments based on a climate model that demonstrates a successful two-year forecast of the La Niña support the hypothesis that warm sea surface temperature (SST) anomalies in the Atlantic and Indian Oceans act to intensify the easterly winds in the central equatorial Pacific and largely contribute to the occurrence and two-year predictability of the 2010–2012 La Niña. The results highlight the importance of increased Atlantic-Indian Ocean SSTs for the multi-year La Niña’s predictability under global warming.
Publisher: American Meteorological Society
Date: 04-1997
Publisher: Springer Science and Business Media LLC
Date: 03-10-2017
DOI: 10.1038/S41598-017-12674-Z
Abstract: In the latter half of 2016 Indonesia and Australia experienced extreme wet conditions and East Africa suffered devastating drought, which have largely been attributed to the occurrence of strong negative Indian Ocean Dipole (IOD) and weak La Niña. Here we examine the causes and predictability of the strong negative IOD and its impact on the development of La Niña in 2016. Analysis on atmosphere and ocean reanalyses and forecast sensitivity experiments using the Australian Bureau of Meteorology’s dynamical seasonal forecast system reveals that this strong negative IOD, which peaked in July-September, developed primarily by the Indian Ocean surface and subsurface conditions. The long-term trend over the last 55 years in sea surface and subsurface temperatures, which is characterised by warming of the tropical Indian and western Pacific and cooling in the equatorial eastern Pacific, contributed positively to the extraordinary strength of this IOD. We further show that the strong negative IOD was a key promoter of the weak La Niña of 2016. Without the remote forcing from the IOD, this weak La Niña may have been substantially weaker because of the extraordinarily long-lasting warm surface condition over the dateline from the tail end of strong El Niño of 2015–16.
Publisher: American Geophysical Union (AGU)
Date: 09-2021
DOI: 10.1029/2021JC017591
Abstract: Sea surface temperature (SST) variability in the western half of the Niño 4 region (Niño‐4W), bounded by 160°E−175°W and 5°S–5°N, has a significant impact on weather and the marine environment of the Indo‐Pacific. It exhibits significant negative skewness, with the strong penetration of the cold tongue into the western Pacific during strong La Niñas but a more muted response during El Niños. Zonal advection plays a dominant role in driving Niño‐4W SST cooling during the strong La Niña events vertical processes also contribute, with air‐sea heat fluxes providing weak negative feedback. Advection also plays a key role in driving the Niño‐4W SST warming, which is not always in sync with El Niño events. Among the advection terms, the advection of mean temperature by zonal velocity anomalies, or zonal advective feedback, plays a key role during the development phase of the warm and cold events. Strong negative air‐sea heat flux anomalies during the development of warm events are linked to the negative SST skewness in the Niño‐4W region.
Publisher: American Geophysical Union (AGU)
Date: 14-12-2016
DOI: 10.1002/2016GL071423
Publisher: American Meteorological Society
Date: 15-08-2012
DOI: 10.1175/JCLI-D-11-00324.1
Abstract: Off the Western Australia coast, interannual variations of wind regime during the austral winter and spring are significantly correlated with the Indian Ocean dipole (IOD) and the southern annular mode (SAM) variability. Atmospheric general circulation model experiments forced by an idealized IOD sea surface temperature anomaly field suggest that the IOD-generated deep atmospheric convection anomalies trigger a Rossby wave train in the upper troposphere that propagates into the southern extratropics and induces positive geopotential height anomalies over southern Australia, independent of the SAM. The positive geopotential height anomalies extended from the upper troposphere to the surface, south of the Australian continent, resulting in easterly wind anomalies off the Western Australia coast and a reduction of the high-frequency synoptic storm events that deliver the majority of southwest Australia rainfall during austral winter and spring. In the marine environment, the wind anomalies and reduction of storm events may h er the western rock lobster recruitment process.
Publisher: American Meteorological Society
Date: 07-2000
Publisher: Springer Science and Business Media LLC
Date: 13-11-2015
Publisher: Elsevier BV
Date: 09-2018
Publisher: Springer Science and Business Media LLC
Date: 24-05-2019
Publisher: American Meteorological Society
Date: 04-10-2013
DOI: 10.1175/JCLI-D-13-00006.1
Abstract: Predictability of the southern annular mode (SAM) for lead times beyond 1–2 weeks has traditionally been considered to be low because the SAM is regarded as an internal mode of variability with a typical decorrelation time of about 10 days. However, the association of the SAM with El Niño–Southern Oscillation (ENSO) suggests the potential for making seasonal predictions of the SAM. In this study the authors explore seasonal predictability and the predictive skill of SAM using observations and retrospective forecasts (hindcasts) from the Australian Bureau of Meteorology dynamical seasonal forecast system [the Predictive Ocean and Atmosphere Model for Australia, version 2 (POAMA2)]. Based on the observed seasonal relationships of the SAM with tropical sea surface temperatures, two distinctive periods of high seasonal predictability are suggested: austral late autumn to winter and late spring to early summer. Predictability of the SAM in the austral cold seasons stems from the association of the SAM with warm-pool (or Modoki/central Pacific) ENSO, whereas predictability in the austral warm seasons stems from the association of the SAM with cold-tongue (or eastern Pacific) ENSO. Using seasonal hindcasts for 1980–2010 from POAMA2, it is shown that the observed relationship between SAM and ENSO is faithfully depicted and SST variations associated with ENSO are skillfully predicted. Consequently, POAMA2 can skillfully predict the phase and litude of seasonal anomalies of the SAM in early summer and early winter for at least one season in advance. Zero-lead monthly forecasts of the SAM are furthermore shown to be highly skillful in almost all months, which is ascribed to predictability stemming from observed atmospheric initial conditions.
Publisher: American Geophysical Union (AGU)
Date: 08-2006
DOI: 10.1029/2006GL026786
Publisher: American Meteorological Society
Date: 18-04-2012
DOI: 10.1175/JCLI-D-11-00501.1
Abstract: Recent research has shown that the climatic impact from El Niño–Southern Oscillation (ENSO) on middle latitudes west of the western Pacific (e.g., southeast Australia) during austral spring (September–November) is conducted via the tropical Indian Ocean (TIO). However, it is not clear whether this impact pathway is symmetric about the positive and negative phases of ENSO and the Indian Ocean dipole (IOD). It is shown that a strong asymmetry does exist. For ENSO, only the impact from El Niño is conducted through the TIO pathway the impact from La Niña is delivered through the Pacific–South America pattern. For the IOD, a greater convection anomaly and wave train response occurs during positive IOD (pIOD) events than during negative IOD (nIOD) events. This “impact asymmetry” is consistent with the positive skewness of the IOD, principally due to a negative skewness of sea surface temperature (SST) anomalies in the east IOD (IODE) pole. In the IODE region, convection anomalies are more sensitive to a per unit change of cold SST anomalies than to the same unit change of warm SST anomalies. This study shows that the IOD skewness occurs despite the greater d ing, rather than due to a breakdown of this d ing as suggested by previous studies. This IOD impact asymmetry provides an explanation for much of the reduction in spring rainfall over southeast Australia during the 2000s. Key to this rainfall reduction is the increased occurrences of pIOD events, more so than the lack of nIOD events.
Publisher: Springer Science and Business Media LLC
Date: 30-04-2010
Publisher: American Geophysical Union (AGU)
Date: 12-03-2011
DOI: 10.1029/2010GL046515
Publisher: Springer Science and Business Media LLC
Date: 26-10-2013
Publisher: American Meteorological Society
Date: 12-2016
Publisher: American Meteorological Society
Date: 1988
Publisher: American Meteorological Society
Date: 27-03-2015
DOI: 10.1175/JCLI-D-14-00582.1
Abstract: This study investigates the causes and predictability of the different springtime rainfall responses over Australia for El Niño in 1997 and 2002. The rainfall deficit over Australia is generally assumed to be linearly related to the strength of El Niño. However, Australia received near-normal springtime rainfall during the record strong El Niño in 1997, whereas it suffered from severe drought, especially in the east, during the weak El Niño of 2002. Statistical reconstruction of the rainfall anomalies and forecasts produced from the Australian Bureau of Meteorology’s dynamical seasonal forecast system [Predictive Ocean and Atmosphere Model for Australia (POAMA)] demonstrated that the eastward and westward shifts of the maximum SST warming of El Niño contributed to the near-normal and dry responses of Australian spring rainfall in 1997 and 2002, respectively. Hence, the contrasting rainfall responses were largely predictable. However, the dry conditions in 2002 were significantly lified by the occurrence of the record strength negative phase of the southern annular mode (SAM), which could only be predicted with the use of realistic atmospheric initial conditions in the atmosphere–ocean coupled configuration of POAMA. Therefore, predictability of the severity of the 2002 drought over Australia was strongly constrained by the predictability of the SAM, despite the high predictability of the drier than normal condition of 2002 spring that stems from the anomalous central Pacific warming of 2002 El Niño.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 14-12-2007
Publisher: American Geophysical Union (AGU)
Date: 19-12-2015
DOI: 10.1002/2015GL067086
Publisher: American Meteorological Society
Date: 09-1982
Publisher: American Meteorological Society
Date: 09-2009
Abstract: The behavior of convection and the Madden–Julian oscillation (MJO) is compared in two simulations from the same global climate model but with two very different treatments of convection: one has a conventional parameterization of moist processes and the other replaces the parameterization with a two-dimensional cloud-resolving model, the so-called superparameterization. The different behavior of local convection and the MJO in the two model simulations reveals that the accurate representation of the following characteristics in the modes of convection might contribute to the improvement of the MJO simulations: (i) precipitation should be an exponentially increasing function of the column saturation fraction, (ii) heavy precipitation should be associated with a stratiform diabatic heating profile, and (iii) there should be a positive relationship between precipitation and surface latent heat flux.
Publisher: Springer Science and Business Media LLC
Date: 20-02-2021
Publisher: American Meteorological Society
Date: 08-02-2012
DOI: 10.1175/JCLI-D-11-00125.1
Abstract: Forecast skill for seasonal mean rainfall across northern Australia is lower during the summer monsoon than in the premonsoon transition season based on 25 years of hindcasts using the Predictive Ocean Atmosphere Model for Australia (POAMA) coupled model seasonal forecast system. The authors argue that this partly reflects an intrinsic property of the monsoonal system, whereby seasonally varying air–sea interaction in the seas around northern Australia promotes predictability in the premonsoon season and demotes predictability after monsoon onset. Trade easterlies during the premonsoon season support a positive feedback between surface winds, SST, and rainfall, which results in stronger and more persistent SST anomalies to the north of Australia that compliment the remote forcing of Australian rainfall from El Niño in the Pacific. After onset of the Australian summer monsoon, this local feedback is not supported in the monsoonal westerly regime, resulting in weaker SST anomalies to the north of Australia and with lower persistence than in the premonsoon season. Importantly, the seasonality of this air–sea interaction is captured in the POAMA forecast model. Furthermore, analysis of perfect model forecasts and forecasts generated by prescribing observed SST results in largely the same conclusion (i.e., significantly lower actual and potential forecast skill during the monsoon), thereby supporting the notion that air–sea interaction contributes to intrinsically lower predictability of rainfall during the monsoon.
Publisher: American Meteorological Society
Date: 2000
Publisher: Meteorological Society of Japan
Date: 1993
Publisher: Springer Science and Business Media LLC
Date: 10-12-2010
Publisher: Springer Science and Business Media LLC
Date: 10-12-2013
Publisher: Springer Science and Business Media LLC
Date: 27-02-2019
DOI: 10.1038/S41598-019-40034-6
Abstract: A strong relationship between the quasi-biennial oscillation (QBO) of equatorial stratospheric winds and the litude of the Madden-Julian oscillation (MJO) during the boreal winter has recently been uncovered using observational data from the mid-1970s to the present. When the QBO is in its easterly phase in the lower stratosphere, it favors stronger MJO activity during boreal winter, while the MJO tends to be weaker during the westerly phase of the QBO. Here we show using reconstructed indices of the MJO and QBO back to 1905 that the relationship between enhanced boreal winter MJO activity and the easterly phase of the QBO has only emerged since the early 1980s. The emergence of this relationship coincides with the recent cooling trend in the equatorial lower stratosphere and the warming trend in the equatorial upper troposphere, which appears to have sensitized MJO convective activity to QBO-induced changes in static stability near the tropopause. Climate change is thus suggested to have played a role in promoting coupling between the MJO and the QBO.
Publisher: Elsevier BV
Date: 06-2021
Publisher: Springer Science and Business Media LLC
Date: 19-02-2014
Publisher: American Geophysical Union (AGU)
Date: 05-01-2015
DOI: 10.1002/2014GL062509
Publisher: American Meteorological Society
Date: 11-2001
Publisher: American Meteorological Society
Date: 08-2004
Publisher: American Meteorological Society
Date: 06-2009
Abstract: The Madden–Julian oscillation (MJO) interacts with and influences a wide range of weather and climate phenomena (e.g., monsoons, ENSO, tropical storms, midlatitude weather), and represents an important, and as yet unexploited, source of predictability at the subseasonal time scale. Despite the important role of the MJO in climate and weather systems, current global circulation models (GCMs) exhibit considerable shortcomings in representing this phenomenon. These shortcomings have been documented in a number of multimodel comparison studies over the last decade. However, diagnosis of model performance has been challenging, and model progress has been difficult to track, because of the lack of a coherent and standardized set of MJO diagnostics. One of the chief objectives of the U.S. Climate Variability and Predictability (CLIVAR) MJO Working Group is the development of observation-based diagnostics for objectively evaluating global model simulations of the MJO in a consistent framework. Motivation for this activity is reviewed, and the intent and justification for a set of diagnostics is provided, along with specification for their calculation, and illustrations of their application. The diagnostics range from relatively simple analyses of variance and correlation to more sophisticated space–time spectral and empirical orthogonal function analyses. These diagnostic techniques are used to detect MJO signals, to construct composite life cycles, to identify associations of MJO activity with the mean state, and to describe interannual variability of the MJO.
Publisher: American Meteorological Society
Date: 03-2011
Abstract: The prediction skill of the Australian Bureau of Meteorology dynamical seasonal forecast model Predictive Ocean Atmosphere Model for Australia (POAMA) is assessed for probabilistic forecasts of spring season rainfall in Australia and the feasibility of increasing forecast skill through statistical postprocessing is examined. Two statistical postprocessing techniques are explored: calibrating POAMA prediction of rainfall anomaly against observations and using dynamically predicted mean sea level pressure to infer regional rainfall anomaly over Australia (referred to as “bridging”). A “homogeneous” multimodel ensemble prediction method (HMME) is also introduced that consists of the combination of POAMA’s direct prediction of rainfall anomaly together with the two statistically postprocessed predictions. Using hindcasts for the period 1981–2006, the direct forecasts from POAMA exhibit skill relative to a climatological forecast over broad areas of eastern and southern Australia, where El Niño and the Indian Ocean dipole (whose behavior POAMA can skillfully predict at short lead times) are known to exert a strong influence in austral spring. The calibrated and bridged forecasts, while potentially offering improvement over the direct forecasts because of POAMA’s ability to predict the main drivers of springtime rainfall (e.g., El Niño and the Southern Oscillation), show only limited areas of improvement, mainly because strict cross-validation limits the ability to capitalize on relatively modest predictive signals with short record lengths. However, when POAMA and the two statistical–dynamical rainfall forecasts are combined in the HMME, higher deterministic and probabilistic skill is achieved over any of the single models, which suggests the HMME is another useful method to calibrate dynamical model forecasts.
Publisher: American Meteorological Society
Date: 12-1985
Publisher: American Meteorological Society
Date: 12-1986
Publisher: American Meteorological Society
Date: 02-1988
Publisher: American Meteorological Society
Date: 04-1991
Publisher: Meteorological Society of Japan
Date: 1994
Publisher: American Meteorological Society
Date: 07-1989
Publisher: Springer Science and Business Media LLC
Date: 15-03-2018
Publisher: American Geophysical Union (AGU)
Date: 09-07-2016
DOI: 10.1002/2016GL069453
Publisher: Springer Science and Business Media LLC
Date: 23-03-2017
Publisher: Springer Science and Business Media LLC
Date: 25-02-2010
Publisher: Springer Science and Business Media LLC
Date: 28-10-2010
Publisher: Springer Science and Business Media LLC
Date: 12-10-2017
Publisher: American Meteorological Society
Date: 09-2008
Abstract: Three aspects of space–time spectral analysis are explored for diagnosis of the organization of tropical convection by the Madden–Julian oscillation (MJO) and other equatorial wave modes: 1) definition of the background spectrum upon which spectral peaks are assessed, 2) alternate variance preserving display of the spectra, and 3) the space–time coherence spectrum. Here the background spectrum at each zonal wavenumber is assumed to result from a red noise process. The associated decorrelation time for the red noise process for tropical convection is found to be half as long as for zonal wind, reflecting the different physical processes controlling each field. The significance of spectral peaks associated with equatorial wave modes for outgoing longwave radiation (OLR), which is a proxy for precipitating deep convection, and zonal winds that stand out above the red background spectrum is similar to that identified using a background spectrum resulting from ad hoc smoothing of the original spectrum. A variance-preserving display of the space–time power spectrum with a logarithmic frequency axis is useful for directly detecting Kelvin waves (periods 5–15 days for eastward zonal wavenumbers 1–5) and for highlighting their distinction from the MJO. The space–time coherence of OLR and zonal wind is predominantly associated with the MJO and other equatorial waves. The space–time coherence is independent of estimating the background spectrum and is quantifiable thus, it is suggested as a useful metric for the MJO and other equatorial waves in observations and simulations. The space–time coherence is also used to quantify the association of Kelvin waves in the stratosphere with convective variability in the troposphere and for detection of barotropic Rossby–Haurwitz waves.
Publisher: American Meteorological Society
Date: 2018
Publisher: Springer Science and Business Media LLC
Date: 26-08-2017
Publisher: Springer Science and Business Media LLC
Date: 08-01-2016
Publisher: American Meteorological Society
Date: 06-1996
Publisher: American Meteorological Society
Date: 08-2011
Abstract: Impacts of El Niño–Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD) on Australian rainfall are diagnosed from the perspective of tropical and extratropical teleconnections triggered by tropical sea surface temperature (SST) variations. The tropical teleconnection is understood as the equatorially trapped, deep baroclinic response to the diabatic (convective) heating anomalies induced by the tropical SST anomalies. These diabatic heating anomalies also excite equivalent barotropic Rossby wave trains that propagate into the extratropics. The main direct tropical teleconnection during ENSO is the Southern Oscillation (SO), whose impact on Australian rainfall is argued to be mainly confined to near-tropical portions of eastern Australia. Rainfall is suppressed during El Niño because near-tropical eastern Australia directly experiences subsidence and higher surface pressure associated with the western pole of the SO. Impacts on extratropical Australian rainfall during El Niño are argued to stem primarily from the Rossby wave trains forced by convective variations in the Indian Ocean, for which the IOD is a primary source of variability. These equivalent-barotropic Rossby wave trains emanating from the Indian Ocean induce changes to the midlatitude westerlies across southern Australia, thereby affecting rainfall through changes in mean-state baroclinicity, west–east steering, and possibly orographic effects. Although the IOD does not mature until austral spring, its impact on Australian rainfall during winter is also ascribed to this mechanism. Because ENSO is largely unrelated to the IOD during austral winter, there is limited impact of ENSO on rainfall across southern latitudes of Australia in winter. A strong impact of ENSO on southern Australia rainfall in spring is ascribed to the strong covariation of ENSO and the IOD in this season. Implications of this pathway from the tropical Indian Ocean for impacts of both the IOD and ENSO on southern Australian climate are discussed with regard to the ability to make seasonal climate predictions and with regard to the role of trends in tropical SST for driving trends in Australian climate.
Publisher: American Meteorological Society
Date: 12-2012
Abstract: In light of the growing recognition of the role of surface temperature variations in the Indian Ocean for driving global climate variability, the predictive skill of the sea surface temperature (SST) anomalies associated with the Indian Ocean dipole (IOD) is assessed using ensemble seasonal forecasts from a selection of contemporary coupled climate models that are routinely used to make seasonal climate predictions. The authors assess predictions from successive versions of the Australian Bureau of Meteorology Predictive Ocean–Atmosphere Model for Australia (POAMA 15b and 24), successive versions of the NCEP Climate Forecast System (CFSv1 and CFSv2), the ECMWF seasonal forecast System 3 (ECSys3), and the Frontier Research Centre for Global Change system (SINTEX-F) using seasonal hindcasts initialized each month from January 1982 to December 2006. The lead time for skillful prediction of SST in the western Indian Ocean is found to be about 5–6 months while in the eastern Indian Ocean it is only 3–4 months when all start months are considered. For the IOD events, which have maximum litude in the September–November (SON) season, skillful prediction is also limited to a lead time of about one season, although skillful prediction of large IOD events can be longer than this, perhaps up to about two seasons. However, the tendency for the models to overpredict the occurrence of large events limits the confidence of the predictions of these large events. Some common model errors, including a poor representation of the relationship between El Niño and the IOD, are identified indicating that the upper limit of predictive skill of the IOD has not been achieved.
Publisher: American Geophysical Union (AGU)
Date: 07-05-2018
DOI: 10.1029/2018GL077207
Publisher: American Meteorological Society
Date: 15-03-2009
Abstract: Impacts of the Madden–Julian oscillation (MJO) on Australian rainfall and circulation are examined during all four seasons. The authors examine circulation anomalies and a number of different rainfall metrics, each composited contemporaneously for eight MJO phases derived from the real-time multivariate MJO index. Multiple rainfall metrics are examined to allow for greater relevance of the information for applications. The greatest rainfall impact of the MJO occurs in northern Australia in (austral) summer, although in every season rainfall impacts of various magnitude are found in most locations, associated with corresponding circulation anomalies. In northern Australia in all seasons except winter, the rainfall impact is explained by the direct influence of the MJO’s tropical convective anomalies, while in winter a weaker and more localized signal in northern Australia appears to result from the modulation of the trade winds as they impinge upon the eastern coasts, especially in the northeast. In extratropical Australia, on the other hand, the occurrence of enhanced (suppressed) rainfall appears to result from induced upward (downward) motion within remotely forced extratropical lows (highs), and from anomalous low-level northerly (southerly) winds that transport moisture from the tropics. Induction of extratropical rainfall anomalies by remotely forced lows and highs appears to operate mostly in winter, whereas anomalous meridional moisture transport appears to operate mainly in the summer, autumn, and to some extent in the spring.
Publisher: IOP Publishing
Date: 11-03-2021
Abstract: Extreme weather and climate events associated with El Niño and La Niña cause massive societal impacts. Therefore, observations and forecasts are used around the world to prepare for such events. However, global warming has caused warm El Niño events to seem bigger than they are, while cold La Niña events seem smaller, in the commonly used Niño3.4 index (sea surface temperature (SST) anomalies over 5 ∘ S–5 ∘ N, 120–170 ∘ W). We propose a simple and elegant adjustment, defining a relative Niño3.4 index as the difference between the original SST anomaly and the anomaly over all tropical oceans (20 ∘ S–20 ∘ N). This relative index describes the onset of convection better, is not contaminated by global warming and can be monitored and forecast in real-time. We show that the relative Niño3.4 index is better in line with effects on rainfall and would be more useful for preparedness for El Niño and La Niña in a changing climate and for El Niño—Southern Oscillation research.
Publisher: American Geophysical Union (AGU)
Date: 10-11-2018
DOI: 10.1029/2018JD029321
Publisher: American Meteorological Society
Date: 25-11-2013
Abstract: A new Madden–Julian oscillation (MJO) index is developed from a combined empirical orthogonal function (EOF) analysis of meridionally averaged 200-hPa velocity potential (VP200), 200-hPa zonal wind (U200), and 850-hPa zonal wind (U850). Like the Wheeler–Hendon Real-time Multivariate MJO (RMM) index, which was developed in the same way except using outgoing longwave radiation (OLR) data instead of VP200, daily data are projected onto the leading pair of EOFs to produce the two-component index. This new index is called the velocity potential MJO (VPM) indices and its properties are quantitatively compared to RMM. Compared to the RMM index, the VPM index detects larger- litude MJO-associated signals during boreal summer. This includes a slightly stronger and more coherent modulation of Atlantic tropical cyclones. This result is attributed to the fact that velocity potential preferentially emphasizes the planetary-scale aspects of the ergent circulation, thereby spreading the convectively driven component of the MJO’s signal across the entire globe. VP200 thus deemphasizes the convective signal of the MJO over the Indian Ocean warm pool, where the OLR variability associated with the MJO is concentrated, and enhances the signal over the relatively drier longitudes of the equatorial Pacific and Atlantic. This work provides a useful framework for systematic analysis of the strengths and weaknesses of different MJO indices.
Publisher: American Meteorological Society
Date: 11-2009
Abstract: The relationship between variations of Indo-Pacific sea surface temperatures (SSTs) and Australian springtime rainfall over the last 30 years is investigated with a focus on predictability of inter–El Niño variations of SST and associated rainfall anomalies. Based on observed data, the leading empirical orthogonal function (EOF) of Indo-Pacific SST represents mature El Niño conditions, while the second and fourth modes depict major east–west shifts of in idual El Niño events. These higher-order EOFs of SST explain more rainfall variance in Australia, especially in the southeast, than does the El Niño mode. Furthermore, intense springtime droughts tend to be associated with peak warming in the central Pacific, as captured by EOFs 2 and 4, together with warming in the eastern Pacific as depicted by EOF1. The ability to predict these inter–El Niño variations of SST and Australian rainfall is assessed with the Australian Bureau of Meteorology dynamical coupled model seasonal forecast system, the Predictive Ocean and Atmospheric Model for Australia (POAMA). A 10-member ensemble of 9-month hindcasts was generated for the period 1980–2006. For the September–November season, the leading 2 EOFs of SST are predictable with lead times of 3–6 months, while SST EOF4 is predictable out to a lead time of 1 month. The teleconnection between the leading EOFs of SST and Australian rainfall is also well depicted in the model. Based on this ability to predict major east–west variations of El Niño and the teleconnection to Australian rainfall, springtime rainfall over eastern Australia, and major drought events are predictable up to a season in advance.
Publisher: American Meteorological Society
Date: 25-11-2013
Abstract: The Australian Bureau of Meteorology has recently enhanced its capability to make coupled model forecasts of intraseasonal climate variations. The Predictive Ocean Atmosphere Model for Australia (POAMA, version 2) seasonal prediction forecast system in operations prior to March 2013, designated P2-S, was not designed for intraseasonal forecasting and has deficiencies in this regard. Most notably, the forecasts were only initialized on the 1st and 15th of each month, and the growth of the ensemble spread in the first 30 days of the forecasts was too slow to be useful on intraseasonal time scales. These deficiencies have been addressed in a system upgrade by initializing more often and through enhancements to the ensemble generation. The new ensemble generation scheme is based on a coupled-breeding approach and produces an ensemble of perturbed atmosphere and ocean states for initializing the forecasts. This scheme impacts favorably on the forecast skill of Australian rainfall and temperature compared to P2-S and its predecessor (version 1.5). In POAMA-1.5 the ensemble was produced using time-lagged atmospheric initial conditions but with unperturbed ocean initial conditions. P2-S used an ensemble of perturbed ocean initial conditions but only a single atmospheric initial condition. The improvement in forecast performance using the coupled-breeding approach is primarily reflected in improved reliability in the first month of the forecasts, but there is also higher skill in predicting important drivers of intraseasonal climate variability, namely the Madden–Julian oscillation and southern annular mode. The results illustrate the importance of having an optimal ensemble generation strategy.
Publisher: Springer Science and Business Media LLC
Date: 09-07-2011
Publisher: American Geophysical Union (AGU)
Date: 10-2009
DOI: 10.1029/2009GL040100
Publisher: American Meteorological Society
Date: 02-1989
Publisher: Wiley
Date: 2009
DOI: 10.1002/QJ.370
Publisher: American Meteorological Society
Date: 27-02-2017
Abstract: Interannual variation of seasonal-mean tropical convection over the Indo-Pacific region is primarily controlled by El Niño–Southern Oscillation (ENSO). For ex le, during El Niño winters, seasonal-mean convection around the Maritime Continent becomes weaker than normal, while that over the central to eastern Pacific is strengthened. Similarly, subseasonal convective activity, which is associated with the Madden–Julian oscillation (MJO), is influenced by ENSO. The MJO activity tends to extend farther eastward to the date line during El Niño winters and contract toward the western Pacific during La Niña winters. However, the overall level of MJO activity across the Maritime Continent does not change much in response to the ENSO. It is shown that the boreal winter MJO litude is closely linked with the stratospheric quasi-biennial oscillation (QBO) rather than with ENSO. The MJO activity around the Maritime Continent becomes stronger and more organized during the easterly QBO winters. The QBO-related MJO change explains up to 40% of interannual variation of the boreal winter MJO litude. This result suggests that variability of the MJO and the related tropical–extratropical teleconnections can be better understood and predicted by taking not only the tropospheric circulation but also the stratospheric mean state into account. The seasonality of the QBO–MJO link and the possible mechanism are also discussed.
Publisher: Springer Science and Business Media LLC
Date: 19-04-2014
Publisher: American Meteorological Society
Date: 09-2005
DOI: 10.1175/JCLI3493.1
Abstract: The evolution of the Indian Ocean during El Niño–Southern Oscillation is investigated in a 100-yr integration of an Australian Bureau of Meteorology coupled seasonal forecast model. During El Niño, easterly anomalies are induced across the eastern equatorial Indian Ocean. These act to suppress the equatorial thermocline to the west and elevate it to the east and initially cool (warm) the sea surface temperature (SST) in the east (west). Subsequently, the entire Indian Ocean basin warms, mainly in response to the reduced latent heat flux and enhanced shortwave radiation that is associated with suppressed rainfall. This evolution can be partially explained by the excitation of an intrinsic coupled mode that involves a feedback between anomalous equatorial easterlies and zonal gradients in SST and rainfall. This positive feedback develops in the boreal summer and autumn seasons when the mean thermocline is shallow in the eastern equatorial Indian Ocean in response to trade southeasterlies. This positive feedback diminishes once the climatological surface winds become westerly at the onset of the Australian summer monsoon. ENSO is the leading mechanism that excites this coupled mode, but not all ENSO events are efficient at exciting it. During the typical El Niño (La Niña) event, easterly (westerly) anomalies are not induced until after boreal autumn, which is too late in the annual cycle to instigate strong dynamical coupling. Only those ENSO events that develop early (i.e., before boreal summer) instigate a strong coupled response in the Indian Ocean. The coupled mode can also be initiated in early boreal summer by an equatorward shift of the subtropical ridge in the southern Indian Ocean, which stems from uncoupled extratropical variability.
Publisher: Springer Berlin Heidelberg
Date: 17-10-2012
Publisher: American Meteorological Society
Date: 12-2002
Publisher: American Geophysical Union (AGU)
Date: 13-01-2016
DOI: 10.1002/2015GL066984
Publisher: Wiley
Date: 07-2018
DOI: 10.1002/QJ.3260
Publisher: Springer Science and Business Media LLC
Date: 20-03-2020
DOI: 10.1038/S41598-020-61482-5
Abstract: Northern Australia wet season (November–April) rainfall exhibits strong variability on multiyear timescales. In order to reveal the underlying mechanisms of this variability, we investigate observational records for the period 1900–2017. At multiyear timescales, the rainfall varies coherently across north-western Australia (NW) and north-eastern Australia (NE), but the variability in these two regions is largely independent. The variability in the NE appears to be primarily controlled by the remote influence of low frequency variations of El Niño-Southern Oscillation (ENSO). In contrast, multiyear variations in the NW appear to be largely driven locally and stem from a combination of rainfall-wind-evaporation feedback, whereby enhanced land-based rainfall is associated with westerly wind anomalies to the west that enhance local evaporation over the ocean to feed the enhanced land based rainfall, and soil moisture-rainfall feedback. Soil-moisture and associated evapotranspiration over northern Australia appear to act as sources of memory for sustaining multiyear wet and dry conditions in the NW. Our results imply that predictability of multiyear rainfall variations over the NW may derive from the initial soil moisture state and its memory, while predictability in the NE will be limited by the predictability of the low frequency variations of ENSO.
Publisher: Wiley
Date: 21-03-2011
DOI: 10.1002/QJ.769
Publisher: Frontiers Media SA
Date: 28-06-2019
Publisher: American Meteorological Society
Date: 11-1989
Publisher: American Meteorological Society
Date: 15-07-2011
Abstract: This study investigates the impact of Indian Ocean sea surface temperature (SST) anomalies on the atmospheric circulation of the Southern Hemisphere during El Niño events, with a focus on Australian climate. During El Niño episodes, the tropical Indian Ocean exhibits two types of SST response: a uniform “basinwide warming” and a dipole mode—the Indian Ocean dipole (IOD). While the impacts of the IOD on climate have been extensively studied, the effects of the basinwide warming, particularly in the Southern Hemisphere, have received less attention. The interannual basinwide warming response has important implications for Southern Hemisphere atmospheric circulation because 1) it accounts for a greater portion of the Indian Ocean monthly SST variance than the IOD pattern and 2) its maximum litude occurs during austral summer to early autumn, when large parts of Australia, South America, and Africa experience their monsoon. Using observations and numerical experiments with an atmospheric general circulation model forced with historical SST from 1949 to 2005 over different tropical domains, the authors show that the basinwide warming leads to a Gill–Matsuno-type response that reinforces the anomalies caused by changes in the Pacific as part of El Niño. In particular, the basinwide warming drives strong subsidence over Australia, prolonging the dry conditions during January–March, when El Niño–related SST starts to decay. In addition to the anomalous circulation in the tropics, the basinwide warming excites a pair of barotropic anomalies in the Indian Ocean extratropics that induces an anomalous anticyclone in the Great Australian Bight.
Publisher: American Meteorological Society
Date: 02-2000
Publisher: Springer Science and Business Media LLC
Date: 20-04-2012
Publisher: American Meteorological Society
Date: 12-2013
Publisher: American Meteorological Society
Date: 03-2017
Abstract: This study focuses on the impact of the Madden–Julian oscillation (MJO)—as monitored by a well-known multivariate index—on large daily precipitation events in West Africa for the period 1981–2014. Two seasons are considered: the near-equatorial wet season in March–May (MAM) and the peak of the West African monsoon during July–September (JAS), when the intertropical convergence zone (ITCZ) is at its most northerly position. Although the MJO-related interannual variation of seasonal mean rainfall is large, the focus here is on the impacts of the MJO on daily time scales because variations in the frequency of intense, short-term, flood-causing, rainfall events are more important for West African agriculture than variations in seasonal precipitation, particularly near the Guinean coast, where precipitation is abundant. Using composites based on thresholds of daily precipitation amounts, changes in mean precipitation and frequency of the heaviest daily events associated with the phase of the MJO are investigated. The expected modulation of mean rainfall by the MJO is much stronger during MAM than during JAS yet the modulation of the largest events (i.e., daily rainfall rates above the 90th percentile) is comparable in both seasons. Conservative statistical tests of local and field significance indicate unambiguous impacts of the MJO of the expected sign during certain phases, but the nature of the impact depends on the local seasonal precipitation regime. For instance, in JAS, the early stages of the MJO increase the risk of flooding in the Sahel monsoon region while providing relief to the dry southern coast.
No related grants have been discovered for Harry H. Hendon.