Andrew G. Marshall

• PhD
• Senior Researcher at Bureau of Meteorology

Diverse characteristics of El Niño Southern Oscillation (ENSO) events challenge the traditional view of tropical coupled ocean-atmosphere systems. The probability of a transition from one type of event to another is influenced by multiple factors of which many are projected to change. Here we assess the likelihood of ENSO transitions in observation...

The increasing frequency and severity of wildfires in Australia, driven by climate change, pose a significant threat to ecosystems, lives, and property. This study examines the impact of climate drivers, specifically El Niño Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Southern Annular Mode (SAM), Madden-Julian Oscillation (MJO), and two...

South-west Western Australia (SWWA) is home to a world class grains industry that is significantly affected by periods of drought. Previous research has shown a link between the Southern Annular Mode (SAM) and rainfall in SWWA, especially during winter months. Hence, the predictability of the SAM and its relationship to SWWA rainfall can potentiall...

In the original publication [...]

Local meteorology over the Great Barrier Reef (GBR) can significantly influence ocean temperatures, which in turn impacts coral ecosystems. While El Niño–Southern Oscillation (ENSO) provides insight into the expected synoptic states, it lacks details of anticipated sub‐seasonal weather variability at local scales. This study explores the influence...

The skill of subseasonal (multiweek) forecasts of tropical‐cyclone (TC) occurrence over the Northern Hemisphere is examined in the Australian Bureau of Meteorology's (BoM) multiweek to seasonal prediction system, ACCESS‐S2. ACCESS‐S2 shows a good representation of the spatial distribution of TCs in the Northern Hemisphere; however, TC track frequen...

As marine heatwaves (MHWs) become more intense and longer lasting due to global warming, understanding the drivers and impacts of these events is crucial for effective marine resource management. This study investigates the influence of El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), Southern Annular Mode (SAM), Sub-Tropical Rid...

The increasing frequency and duration of severe fire events in Australia further necessitate accurate and timely forecasting to mitigate their consequences. This study evaluated the performance of two distinct approaches to forecasting extreme fire danger at two- to three-week lead times for the period 2003 to 2017: the official Australian climate...

Exposure to weather extremes, such as heatwaves, can cause discomfort, harm, or death in grazing cattle in pastures. While the Australian Bureau of Meteorology issues sheep graziers alerts when there is an exposure risk to chill for livestock, there is no equivalent alert for heat stress for Australian cattle. Before any such alert system can be de...

Local meteorology over the Great Barrier Reef (GBR) can significantly influence ocean temperatures, which in turn impacts coral ecosystems. While El Niño–Southern Oscillation (ENSO) provides insight into the expected synoptic states, it lacks details of the anticipated sub-seasonal weather variability at local scales. This study explores the influe...

According to the Australian Bureau of Meteorology, the northern Australian wet season extends through to April, which also formally marks the end of Australia’s tropical cyclone season. Mid-autumn is when the tropical dry season transition period begins, when crop farmers prepare land for annual crops or pasture–fodder harvest, or when beef cattle...

Fire danger poses a pressing threat to ecosystems and societies worldwide. Adequate preparation and forewarning can help reduce these threats, but these rely on accurate prediction of extreme fire danger. With the knowledge that climatic conditions contribute heavily to overall fire danger, this study evaluates the skill with which episodes of extr...

The variability and distribution of Australia’s summer rainfall are influenced by modes of climate variability on multi-week to multi-year time scales. Here, we investigate the role of the stratospheric quasi-biennial oscillation (QBO) and demonstrate that the QBO influences rainfall variations and extremes’ responses across large regions of Austra...

Aims We investigate the associations between major Australian climate drivers and extreme weekly fire danger throughout the year. Methods We use a composite-based approach, relating the probability of top-decile observed potential fire intensity to the positive and negative modes of the El Niño Southern Oscillation, Indian Ocean Dipole, Madden–Jul...

As marine heatwaves (MHWs) become more intense and longer lasting due to global warming, understanding the drivers and impacts of these events is crucial for effective marine resource management. This study investigates the influence of El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), Southern Annular Mode (SAM), Sub-Tropical Rid...

Extended warning of above‐average and extreme precipitation is valuable to a wide range of stakeholders. However, the sporadic nature of precipitation makes it difficult to forecast skilfully beyond one week. Subseasonal forecasting is a growing area of science that aims to predict average weather conditions multiple weeks in advance using dynamica...

The skill of subseasonal (multiweek) forecasts of tropical cyclone (TC) occurrence over the Southern Hemisphere is examined in the Australian Bureau of Meteorology's (BoM) multiweek to seasonal prediction system, ACCESS‐S2. Relative to its predecessor, ACCESS‐S1, ACCESS‐S2 shows improved biases in spatial TC frequency in the South Pacific and South...

Marine heatwaves (MHWs) can severely impact marine biodiversity, fisheries, and aquaculture. Consequently, there is an increasing desire to understand the drivers of these events to inform their predictability so that proactive decisions may be made to reduce potential impacts. In the Tasman Sea (TS), several relatively intense and broad-scale MHWs...

ACCESS-S2 is a major upgrade to the Australian Bureau of Meteorology’s multi-week to seasonal prediction system. It was made operational in October 2021, replacing ACCESS-S1. The focus of the upgrade is the addition of a new weakly coupled data assimilation system to provide initial conditions for atmosphere, ocean, land and ice fields. The model i...

We examine impacts of the Madden–Julian Oscillation (MJO) on Australian springtime temperatures and extremes, explore the mechanisms behind the teleconnections, and assess their prediction in retrospective forecasts using the Bureau of Meteorology’s ACCESS-S1 dynamical forecast system. The MJO incites strong and significant warming across southern...

We assess seasonally-varying impacts of the Madden-Julian Oscillation (MJO) on Australian maximum and minimum temperature anomalies and extremes, and their modulation by the El Niño – Southern Oscillation (ENSO), for the period June 1974 to May 2022. Our composite-based approach uses observed temperatures from the Australian Gridded Climate Data, a...

Since 2017, the Northern Australia Climate Program (NACP) has assisted the pastoral grazing industry to better manage drought risk and climate variability. The NACP funding is sourced from the beef cattle industry, government, and academia, representing the program’s broad range of aims and target beneficiaries. The program funds scientists in the...

This study first re-examines the impact of the Madden–Julian oscillation (MJO) on weekly rainfall probabilities and wind anomalies across Australia, motivated by the need for a contemporary understanding of the MJO’s influence on Australian rainfall, whether this has changed from a previous assessment published in 2009. With an extra 15 years of ob...

We assess the ability of the Bureau of Meteorology’s ACCESS-S1 dynamical forecast system to simulate and predict extreme fire weather over Australia during austral spring (SON) and summer (DJF) on subseasonal timescales. Specifically, we focus on the roles of the El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Southern Annular Mode...

The austral spring climate of 2020 was characterised by the occurrence of La Niña, which is the most predictable climate driver of Australian springtime rainfall. Consistent with this La Niña, the Bureau of Meteorology’s dynamical sub-seasonal to seasonal forecast system, ACCESS-S1, made highly confident predictions of wetter-than-normal conditions...

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 Niña...

We assessed the ability of the Bureau of Meteorology’s ACCESS-S1 dynamical forecast system to simulate and predict high rainfall extremes for each season over Australia, especially focusing on the role of the Madden-Julian Oscillation (MJO). Using retrospective forecasts for the period 1990–2012, we show that ACCESS-S1 simulated the observed modula...

This study aims to provide an insight into why the Australian spring climate of 2020 was not as wet as predicted by both statistical and dynamical forecast models despite the occurrence of the decent strength of La Nina. Only moderate warming of the SSTs north of Australia, an early demise of the negative Indian Ocean dipole mode, and the suppresse...

We explore the causes and predictability of extreme low minimum temperatures (Tmin) that occurred across northern and eastern Australia in September 2019. Historically, reduced Tmin is related to the occurrence of a positive Indian Ocean Dipole (IOD) and central Pacific El Niño. Positive IOD events tend to locate an anomalous anticyclone over the G...

Plain Language Summary El Niño Southern Oscillation events are extremely important for many countries around the world due to their impacts on rainfall. By separating El Niño into central Pacific (CP) and eastern Pacific (EP) events, we show that the strength of a CP event controls the rainfall amount for southeastern Australia. The stronger a CP e...

ACCESS-S1 will be the next version of the Australian Bureau of Meteorology's seasonal prediction system, due to become operational in early 2018. The multiweek and seasonal performance of ACCESS-S1 has been evaluated based on a 23-year hindcast set and compared to the current operational system, POAMA. The system has considerable enhancements compa...

In this study, we analyze the influence of the Pacific‐South American modes (PSA‐1 and PSA‐2) on the global wind‐wave climate using wave data derived from a WAVEWATCH III global wave hindcast. We apply an empirical orthogonal function analysis to daily‐averaged directional wave spectra to extract the two main patterns of interannual wave spectral v...

Seasonal climate prediction to date has largely focussed on probabilistic forecasts for above‐ and below‐average conditions in climate means. Here, we examine the possibility of making sub‐seasonal to seasonal outlooks for daily‐scale precipitation extremes in Australia. We first use observational data to show that significant relationships exist b...

We assess the impact of split-flow blocking in the Australian region on global ocean wind waves using 30 years of high-resolution wave data from the CAWCR wave model hindcast. Statistically significant anomalies in significant wave height (Hs), peak wave period (Tp) and zonal wave energy flux (CgE) are found to covary with local variations in surfa...

The stratosphere can have a significant impact on winter surface weather on subseasonal to seasonal (S2S) timescales. This study evaluates the ability of current operational S2S prediction systems to capture two important links between the stratosphere and troposphere: (1) changes in probabilistic prediction skill in the extratropical stratosphere...

The stratosphere has been identified as an important source of predictability for a range of processes on subseasonal to seasonal (S2S) time scales. Knowledge about S2S predictability within the stratosphere is however still limited. This study evaluates to what extent predictability in the extratropical stratosphere exists in hindcasts of operatio...

Recent studies have shown that the Madden-Julian Oscillation (MJO) is significantly modulated by the stratospheric Quasi-Biennial Oscillation (QBO). In general, boreal winter MJO becomes more active during the easterly phase of the QBO (EQBO) than during the westerly phase (WQBO). Based on this finding, here we examine the possible impacts of the Q...

We assess the ability of the Bureau of Meteorology’s new ACCESS-S1 dynamical forecast system to predict the MJO using retrospective forecasts for the period 1990–2012. Compared to the benchmark POAMA-2 system, ACCESS-S1 demonstrates improved skill in predicting the ensemble mean bivariate RMM index by about 4 days lead time in austral summer and 5...

A strong relationship between the quasi-biennial oscillation (QBO) of equatorial stratospheric winds and the amplitude 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 stro...

This chapter summarizes current efforts to predict on sub-seasonal timescale monsoons features such as the beginning/end dates, duration, accumulated precipitation, and active/break phases. We present analyses related to the spatial coherence of rainfall anomalies at sub-seasonal 7-90 days timescales , retrospective sub-seasonal forecasts of monsoo...

We assess the impact of the Southern Annular Mode (SAM) on global ocean wind waves using 30 years of wave data from a wave model hindcast that is forced with high resolution surface winds from the NCEP-CFSR reanalysis. Our primary focus is on the wave field and swell influence in the Southern Hemisphere, and we apply our analysis to each of the fou...

This chapter summarizes current efforts to predict monsoons features (such as the beginning/end dates, duration, accumulated precipitation, and active/break phases) on sub-seasonal timescales. The spatial scales of rainfall anomaly in various time scales as well as retrospective forecasts of onset and demise of regional-scale monsoon seasons are co...

The Australian Bureau of Meteorology (BoM) seasonal forecasting system (ACCESS-S1), based on the UK Met Office Global Seasonal forecast system version 5 (GloSea5), is investigated for the prediction of the weekly occurrence of tropical cyclone (TC) activity in the Southern Hemisphere. On multi-week timescales the Madden-Julian Oscillation (MJO) has...

During austral summer 2015-16, prolonged extreme ocean warming events, known as marine heatwaves (MHWs), occurred in the waters around tropical Australia. MHWs arose first in the southeast tropical Indian Ocean in November 2015, emerging progressively east until March 2016, when all waters from the North West Shelf to the Coral Sea were affected. T...

Prediction of regional-scale seasonal amounts of rainfall across the tropical zone is now routinely issued by several research centers, at least since the major warm El Niño Southern Oscillation event of 1997-98. Consisting of at least a 3-month period and grid-points covering several degrees of longitude/latitude, seasonal timescales emphasize the...

The Madden–Julian oscillation (MJO) during boreal winter is observed to be stronger during the easterly phase of the quasi-biennial oscillation (QBO) than during the westerly phase, with the QBO zonal wind at 50 hPa leading enhanced MJO activity by about 1 month. Using 30 years of retrospective forecasts from the POAMA coupled model forecast system...

ACCESS-S1 will be the next version of the Australian Bureau of Meteorology's seasonal prediction system, due to become operational in early 2018. The multiweek and seasonal performance of ACCESS-S1 has been evaluated based on a 23-year hindcast set and compared to the current operational system, POAMA. The system has considerable enhancements compa...

Climate variables, water availability and soil data, are generally considered to be the most important environmental information for determining the agricultural suitability of particular locations. Equivalent sized catchments in south-eastern Australia have about ten times more climate stations than those of northern Australia’s Fitzroy, Darwin an...

We describe a new approach for presenting probabilistic forecasts of the Madden-Julian Oscillation (MJO) based on the community standard Real-time Multivariate MJO (RMM) index, using forecasts from version 2 of the Predictive Ocean Atmosphere Model for Australia. This new display overcomes the difficulty of interpreting a dispersive ensemble plume...

Climate influences marine ecosystems on a range of time scales, from weather-scale (days) through to climate-scale (hundreds of years). Understanding of interannual to decadal climate variability and impacts on marine industries has received less attention. Predictability up to 10 years ahead may come from large-scale climate modes in the ocean tha...

Subseasonal prediction of Australian summer monsoon anomalies is assessed using 30years of retrospective forecasts from version 2 of the Predictive Ocean Atmosphere Model for Australia. Active and break monsoon rainfall episodes are associated with large-scale cyclonic westerly and anticyclonic easterly winds, respectively, for which the Madden-Jul...

A Madden-Julian Oscillation (MJO) event dramatically amplified at the beginning of March 2015 as the convective phase traversed an unusually warm central Pacific Ocean. This record amplification also resulted in record amplitude of the MJO based on index measurements since 1974. We explore the possible role of the anomalously high ocean surface tem...

There has been increasing demand in Australia for extended-range forecasts of extreme heat events. An assessment ismade of the subseasonal experimental guidance provided by the Bureau of Meteorology's seasonal prediction system, Predictive Ocean Atmosphere Model for Australia (POAMA, version 2), for the three most extreme heat events over Australia...

We assess the impact of the tropical Madden Julian Oscillation (MJO) on global ocean wind waves using 30 years of wave data from a wave model hindcast that is forced with high resolution surface winds from the NCEP–CFSR reanalysis. We concentrate on the boreal winter season when the MJO has its greatest amplitude and is potentially a source of pred...

Marine heat waves along the Western Australian coast are potentially damaging to the marine environment especially coastal fisheries and the Ningaloo Reef. Initiation and amplification mechanisms for marine heat waves (referred to as ‘Ningaloo Niño’ events) are explored using ocean and atmosphere reanalyses for the period 1960–2011. We find that th...

Ningaloo Niño refers to the episodic occurrence of anomalously warm ocean conditions along the subtropical coast of Western Australia (WA). Ningaloo Niño typically develops in austral spring, peaks in summer and decays in autumn, and often occurs in conjunction with La Niña conditions in the Pacific which promote poleward transport of warm tropical...

The seasonal cycle of blocking in the Australian region is shown to be associated with major seasonal temperature changes over continental Antarctica (approximately 15°-35°C) and Australia (about 8°-17°C) and with minor changes over the surrounding oceans (below 5°C). These changes are superimposed on a favorable background state for blocking in th...

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 a...

We assess the occurrence and probability of extreme heat over Australia in association with the Southern Annular Mode (SAM), persistent anticyclones over the Tasman Sea, and the Madden–Julian Oscillation (MJO), which have previously been shown to be key drivers of intra-seasonal variations of Australian climate. In this study, extreme heat events a...

We assess the depiction and prediction of blocking at 140°E and its impact on Australian intra-seasonal climate variability in the Bureau of Meteorology’s dynamical intra-seasonal/seasonal forecast model Predictive Ocean Atmosphere Model for Australia version 2 (POAMA-2). The model simulates well the strong seasonality of blocking but underestimate...

The Predictive Ocean Atmosphere Model for Australia (POAMA) is a state-of-the-art intra-seasonal to seasonal forecast system based on a coupled climate model and ocean/atmosphere/land observations assimilation system. Several versions of the POAMA system have been developed over the past decade, including 1.0, 1.5, 2.0 and 2.4. The development of a...

The large sea surface temperature variations induced by the Madden-Julian Oscillation (MJO) on the northwest shelf of Australia and the remote influence of the MJO on the subtropical Western Australian coast are explored using the POAMA Ensemble Ocean Data Assimilation System reanalyses (PEODAS) for the period 1980–2010. The focus here is during th...

We assess the ability of the Predictive Ocean Atmosphere Model for Australia (POAMA) to simulate and predict weekly rainfall associated with the MJO using a 27-year hindcast dataset. After an initial 2-week atmospheric adjustment, the POAMA model is shown to simulate well, both in pattern and in intensity, the weekly-mean rainfall variation associa...

We assess the ability of the Predictive Ocean Atmosphere Model for Australia (POAMA) to simulate and predict the Southern Annular Mode (SAM) and its influence on Australian intra-seasonal climate using a 27-year hindcast dataset. The analysis consists of three stages: (1) prediction of the SAM, (2) simulation of SAM climate anomalies over Australia...

This study examines the potential use of the Predictive Ocean Atmosphere Model for Australia (POAMA), the Bureau of Meteorology's dynamical seasonal forecast system, as an intraseasonal prediction tool for Australia. This would fill the current prediction capability gap between weather forecasts and seasonal outlooks for Australia. The intraseasona...

Extreme heat waves occurred over much of southern and eastern Australia during the summer (27 January-8 February) and winter (14-31 August) of 2009. The summer heat wave resulted in many temperature records across southeastern Australia, as well as devastating bushfires in Victoria that caused losses of life and property. The winter heat wave prima...

The impact of stratospheric resolution on the predictability of stratospheric sudden warming (SSW) events and their effect on European climate is cleanly assessed in two versions of the Hadley Center's atmospheric climate model, Hadley Center global environmental model. The standard 38-level version of the model extends to an altitude of 39 km (∼3...

There is widely believed to be a link between stratospheric flow variability and stationary, persistent “blocking” weather systems, but the precise nature of this link has proved elusive. Using data from the ERA-40 Reanalysis and an atmospheric general circulation model (GCM) with a well-resolved stratosphere (HadGAM), it is shown that there are in...

The impact of explosive volcanic eruptions on the atmospheric circulation at high northern latitudes is assessed in two versions of the Met Office Hadley Centre's atmospheric climate model. The standard version of the model extends to an altitude of around 40 km, while the extended version has enhanced stratospheric resolution and reaches 85-km alt...

The European winter surface climate response to the Quasi-Biennial Oscillation (QBO) and its dependence on stratospheric resolution is cleanly assessed in idealized seasonal hindcasts with two versions of the Hadley Centre's atmospheric general circulation model. The standard 38-level version extends to an altitude of 39 km while the extended 60-le...

The Indian Ocean Dipole (IOD) mode of variability has been observed to influence atmospheric circulation and precipitation over the Indian Ocean basin and surrounding continental areas, interacting with the Asian monsoon and El Niño Southern Oscillation (ENSO). Paleo-IOD reconstructions from fossil corals from the eastern tropical Indian Ocean sugg...

The impact of stratospheric resolution on seasonal forecast skill for Europe is cleanly assessed in two versions of the Hadley Centre's atmospheric climate model HadGEM2-A. The standard version of the model with 38 levels extends to an altitude of 39km, while the extended version with 60 levels has enhanced stratospheric resolution and reaches 84km...

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. A...

Systematic errors in climate models are usually addressed in a number of ways, but current methods often make use of model climatological fields as a starting point for model modification. This approach has limitations due to non-linear feedback mechanisms which occur over longer timescales and make the source of the errors difficult to identify. I...

This paper presents an analysis of Northern Hemisphere climate regime variability for three different time slices, simulated by the Fast Ocean Atmosphere Model (FOAM). The three time slices are composed of present-day conditions, the mid-Holocene, and the Last Glacial Maximum (LGM). Climate regimes have been determined by analyzing the structure of...

A multivariate reduced form model was used to investigate the sensitivity of the Australian summer monsoon, as simulated by the Fast Ocean Atmosphere Model (FOAM), to climate forcing changes over the last 55,000 years. A synthesis of palaeoenvironmental observations was used to constrain FOAM for six time slices: 55, 35, 21, 11, 6, and 0 ka. The re...

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 re...

A set of simulations with the Fast Ocean Atmosphere Model (FOAM) are used to investigate variability of the Indian Ocean Dipole (IOD) and interactions with the Australian summer monsoon over the late Quaternary. Time slices simulations were carried out for 55, 35, 21, 11, 6 and 0 ka, allowing the response of the IOD and monsoon to be investigated f...

Burning has been a near-continuous feature of the Australian environment but has become progressively more important since the mid-Tertiary, associated with the development of the characteristic sclerophyll vegetation. In the Quaternary, the extent of burning has varied temporally and regionally with glacial-interglacial cyclicity. Burning during g...

The status of the numerical reproduction of the Madden–Julian Oscillation (MJO) by current global models was assessed through diagnoses of four pairs of coupled and uncoupled simulations. Slow eastward propagation of the MJO, especially in low-level zonal wind, is realistic in all these simulations. However, the simulated MJO suffers from several c...

Dry season fires are probably the largest natural and anthropogenic disturbance in the Australian tropical savannas. A large fraction of this biome is burned annually. The changed surface properties immediately following a fire and during the regrowth period can lead to a significant modification of the surface-atmosphere coupling. A fire/regrowth...

We use the Fast Ocean Atmosphere Model (FOAM) to investigate the variation in the Australian summer monsoon over the last 55 000 years. A synthesis of palaeoenvironmental observations is used to constrain the model for six time slices: 55, 35, 21, 11, 6 and 0 ka. Both inter-hemispheric forcing and the seasonal timing of local insolation changes pla...

Abstract A model intercomparison study was performed to assess the large-scale characteristics of the Australian summer monsoon in a suite of uncoupled, high-resolution coupled and low-resolution coupled general circulation model (GCM) simulations, in comparison to observed,and re-analysis data. While the large-scale characteristics of the ,monsoon...