Articles | Volume 6, issue 4
https://doi.org/10.5194/wcd-6-1643-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-6-1643-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
03 Dec 2025
Research article |
| 03 Dec 2025
| 03 Dec 2025
Intensifying precipitation over the Southern Ocean challenges reanalysis-based climate estimates – Insights from Macquarie Island's 45-year record
School of Earth, Atmosphere and Environment, Monash University, Melbourne, 3800, Australia
Australian Research Council Special Research Initiative for Securing Antarctica's Environmental Future, Melbourne, 3800, Australia
Andrew T. Prata
CSIRO Environment, Melbourne, 3168, Australia
Peter T. May
School of Earth, Atmosphere and Environment, Monash University, Melbourne, 3800, Australia
Ariaan Purich
School of Earth, Atmosphere and Environment, Monash University, Melbourne, 3800, Australia
Australian Research Council Special Research Initiative for Securing Antarctica's Environmental Future, Melbourne, 3800, Australia
School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Melbourne, 3010, Australia
Australian Research Council Centre of Excellence for the Weather of the 21st Century, Melbourne, 3010, Australia
Steven T. Siems
School of Earth, Atmosphere and Environment, Monash University, Melbourne, 3800, Australia
Australian Research Council Special Research Initiative for Securing Antarctica's Environmental Future, Melbourne, 3800, Australia
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Xiaoshen Sun, Chris Medcraft, Ramon Braga, Peter Butcherine, Zoran Ristovski, Steven Siems, Christian J. Sanders, and Daniel P. Harrison
EGUsphere, https://doi.org/10.5194/egusphere-2026-1729, https://doi.org/10.5194/egusphere-2026-1729, 2026
This preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).
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We propose a novel method to detect and track sea spray particles released during marine cloud brightening (MCB) over the Great Barrier Reef. Using aircraft measurements, we showed that these released particles can be separated from the research ship and aircraft exhaust and tracked as they spread horizontally and vertically. This improves our ability to trace added sea spray aerosols and supports future work on how they may affect clouds.
Alanah Chapman, Yi Huang, and Claire Vincent
Weather Clim. Dynam., 7, 1265–1284, https://doi.org/10.5194/wcd-7-1265-2026, https://doi.org/10.5194/wcd-7-1265-2026, 2026
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Mass coral bleaching on the Great Barrier Reef is driven by unusually warm ocean temperatures, but cloud cover also plays a critical role by regulating how much sunlight reaches the ocean. This study examines daily patterns of clouds and rainfall over north-east Queensland during bleaching seasons using satellite, radar, and regional weather data. Clouds and rainfall patterns differ between land, ocean and wind conditions, helping improve understanding of processes influencing reef heat stress.
Lara S. Richards, Yi Huang, Michael A. Barnes, Chenhui Jin, Fadhlil R. Muhammad, Daniel P. Harrison, and Steven T. Siems
EGUsphere, https://doi.org/10.5194/egusphere-2026-2114, https://doi.org/10.5194/egusphere-2026-2114, 2026
This preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).
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The doldrums are regions of light winds and relatively clear skies found in the tropics. They often occur during severe coral bleaching events on the Great Barrier Reef yet remain poorly understood. This study examines why the doldrums form and persist, identifying how both tropical and extratropical weather systems align to first form the doldrums and that the stalling of these weather systems prolongs the doldrums persistence.
Elio Campitelli, Ariaan Purich, Julie Arblaster, Eun-Pa Lim, Matthew C. Wheeler, and Phillip Reid
The Cryosphere, 20, 2557–2587, https://doi.org/10.5194/tc-20-2557-2026, https://doi.org/10.5194/tc-20-2557-2026, 2026
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By comparing sea-ice forecasts made by the same model but using different initial conditions, we show that better initial sea-ice initial conditions improve sea-ice forecasts a lot in Summer and Autumn, but not as much in winter. This means that forecasting groups should focus efforts in assimilating observations in Summer and that research on how easy it is to predict sea ice need to analyse all seasons.
Caleb Mynard, Emily B. Franklin, Joel Alroe, Karen Westwood, Brandon J. McNabb, Robert Strzepek, Philippe D. Tortell, Steven T. Siems, Antonio Patti, Suzie Molloy, Alan Griffiths, Branka Miljevic, Marc D. Mallet, Ruhi Humphries, and Erin Dunne
EGUsphere, https://doi.org/10.5194/egusphere-2026-1346, https://doi.org/10.5194/egusphere-2026-1346, 2026
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Marine sulfur gases help form climate-cooling particles, but their controls over the Southern Ocean are unclear. During a summer research voyage we measured these gases and linked them to ocean and atmospheric conditions. Near Antarctica, coastal blooms drove sharp rises in dimethyl sulfide while methanethiol remained low. Over the open ocean, both gases varied together, mainly influenced by ocean mixing and temperature, suggesting models should treat coastal and open ocean regions separately.
Andrew G. Pauling, Inga J. Smith, Torge Martin, Jeff K. Ridley, David P. Stevens, Max Thomas, Rebecca L. Beadling, Christopher Danek, Tore Hattermann, Qian Li, John Marshall, Morven Muilwijk, Ariaan Purich, and Neil C. Swart
EGUsphere, https://doi.org/10.5194/egusphere-2026-658, https://doi.org/10.5194/egusphere-2026-658, 2026
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Climate models typically do not include meltwater entering the Southern Ocean due to Antarctic ice sheet mass loss. Previous work shows this meltwater drives sea ice growth, but the varying responses have been difficult to compare across models. We ran 11 climate models using the same meltwater input and found a wide range of sea ice responses depending on the background state in each model. Understanding this uncertainty in response is important for future projections of Antarctic sea ice.
Wenhui Zhao, Yi Huang, Steven Siems, and Daniel Harrison
EGUsphere, https://doi.org/10.5194/egusphere-2026-1251, https://doi.org/10.5194/egusphere-2026-1251, 2026
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Using convection-permitting WRF simulations, this study examines how marine cloud brightening over the GBR depends on aerosol emission strength and spatial distribution. Densely spaced sources generate more uniform aerosol enhancements and stronger cloud microphysical responses than sparsely distributed sources, despite identical emissions. CDNC and optical depth increase strongly, indicating a dominant Twomey effect, while cloud water and coverage respond weakly.
Anna M. Ukkola, Steven Thomas, Elisabeth Vogel, Ulrike Bende-Michl, Steven Siems, Vjekoslav Matic, and Wendy Sharples
Hydrol. Earth Syst. Sci., 30, 1463–1485, https://doi.org/10.5194/hess-30-1463-2026, https://doi.org/10.5194/hess-30-1463-2026, 2026
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Future drought changes in Australia –the driest inhabited continent on Earth– have remained stubbornly uncertain. We assess future drought changes in Australia using projections from climate and hydrological models. We show an increasing probability of drought in highly-populated and agricultural regions of Australia in coming decades, suggesting potential impacts on agricultural activities, ecosystems and urban water supply.
Arathy A. Kurup, Caroline Poulsen, Steven T. Siems, and Daniel J. V. Robbins
Atmos. Meas. Tech., 19, 1487–1514, https://doi.org/10.5194/amt-19-1487-2026, https://doi.org/10.5194/amt-19-1487-2026, 2026
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Southern Ocean (SO) clouds are crucial in defining the Earth's radiation budget. They are primarily observed by satellites, due to a lack of surface observations. This study validated cloud top height and cloud mask and compared the microphysics products from 3 satellite cloud datasets over the SO. The study revealed significant differences in cloud property retrievals between the sensors. Multilayer clouds play a major role in the differences when validated with active satellite measurements.
Morven Muilwijk, Tore Hattermann, Rebecca L. Beadling, Neil C. Swart, Aleksi Nummelin, Chuncheng Guo, David M. Chandler, Petra M. Langebroek, Shenjie Zhou, Pierre Dutrieux, Jia-Jia Chen, Christopher Danek, Matthew H. England, Stephen M. Griffies, F. Alexander Haumann, André Jüling, Ombeline Jouet, Qian Li, Torge Martin, John Marshall, Andrew G. Pauling, Ariaan Purich, Zihan Song, Inga J. Smith, Max Thomas, Irene Trombini, Eveline C. van der Linden, and Xiaoqi Xu
The Cryosphere, 20, 1087–1117, https://doi.org/10.5194/tc-20-1087-2026, https://doi.org/10.5194/tc-20-1087-2026, 2026
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Antarctic meltwater affects ocean stratification and temperature, which in turn influences the rate of ice shelf melting – a coupling missing in most climate models. We analyze a suite of climate models with added meltwater to explore this feedback in different regions. While meltwater generally enhances ocean warming and melt, in West Antarctica most models simulate coastal cooling, suggesting a negative feedback that could slow future ice loss there.
Lara S. Richards, Steven T. Siems, Yi Huang, Daniel P. Harrison, and Wenhui Zhao
Weather Clim. Dynam., 7, 109–127, https://doi.org/10.5194/wcd-7-109-2026, https://doi.org/10.5194/wcd-7-109-2026, 2026
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By studying the variability of the trade winds during the Great Barrier Reef coral bleaching season, we show that ocean heating and a higher risk of coral bleaching are linked to the breakdown of the trade winds into either calm and clear conditions or a monsoon-like northerly flow. Years with mass coral bleaching are also associated with more "calm and clear" days in the warmest months and fewer strong trade wind days on the fringe months of the bleaching season.
A. V. Sreenath, Tahereh Alinejadtabrizi, Steven Siems, Peter T. May, Haifeng Zhang, and Eric Schulz
Weather Clim. Dynam., 6, 1797–1813, https://doi.org/10.5194/wcd-6-1797-2025, https://doi.org/10.5194/wcd-6-1797-2025, 2025
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Using 14 years of observations from mooring, we reported that cold air advection creates intense surface flux exchange over the southern ocean, linked with strong boundary layer instability. Results also indicate that cold air advection creates frequent open mesoscale cellular convective clouds. The flux exchange for open and closed mesoscale cellular convective clouds is comparable, suggesting a limited role of the surface flux in the transition of these boundary layer clouds.
Helen J. Shea, Ailie Gallant, Ariaan Purich, and Tessa R. Vance
Clim. Past, 21, 2009–2030, https://doi.org/10.5194/cp-21-2009-2025, https://doi.org/10.5194/cp-21-2009-2025, 2025
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Ice core data from Mount Brown South (MBS), East Antarctica links high sea salt years to stronger westerly winds and increased sea ice near MBS's northeast coast. Low pressure storms off the coast might transport sea salts from sea ice regions to MBS. The tropical Pacific influences sea salt levels with El Niño events affecting wind patterns around MBS, impacting sea salt sources. Identifying these mechanisms aids in the understanding of climate variability before instrumental records.
Jessica M. A. Macha, Andrew N. Mackintosh, Felicity S. McCormack, Benjamin J. Henley, Helen V. McGregor, Christiaan T. van Dalum, and Ariaan Purich
The Cryosphere, 19, 1915–1935, https://doi.org/10.5194/tc-19-1915-2025, https://doi.org/10.5194/tc-19-1915-2025, 2025
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Extreme El Niño–Southern Oscillation (ENSO) events have global impacts, but their Antarctic impacts are poorly understood. Examining Antarctic snow accumulation anomalies of past observed extreme ENSO events, we show that accumulation changes differ between events and are insignificant during most events. Significant changes occur during 2015/16 and in Enderby Land during all extreme El Niños. Historical data limit conclusions, but future greater extremes could cause Antarctic accumulation changes.
Tahereh Alinejadtabrizi, Yi Huang, Francisco Lang, Steven Siems, Michael Manton, Luis Ackermann, Melita Keywood, Ruhi Humphries, Paul Krummel, Alastair Williams, and Greg Ayers
Atmos. Chem. Phys., 25, 2631–2648, https://doi.org/10.5194/acp-25-2631-2025, https://doi.org/10.5194/acp-25-2631-2025, 2025
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Clouds over the Southern Ocean are crucial to Earth's energy balance, but understanding the factors that control them is complex. Our research examines how weather patterns affect tiny particles called cloud condensation nuclei (CCN), which influence cloud properties. Using data from Kennaook / Cape Grim, we found that winter air from Antarctica brings cleaner conditions with lower CCN, while summer patterns from Australia transport more particles. Precipitation also helps reduce CCN in winter.
Daniel J. V. Robbins, Caroline A. Poulsen, Steven T. Siems, Simon R. Proud, Andrew T. Prata, Roy G. Grainger, and Adam C. Povey
Atmos. Meas. Tech., 17, 3279–3302, https://doi.org/10.5194/amt-17-3279-2024, https://doi.org/10.5194/amt-17-3279-2024, 2024
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Extreme wildfire events are becoming more common with climate change. The smoke plumes associated with these wildfires are not captured by current operational satellite products due to their high optical thickness. We have developed a novel aerosol retrieval for the Advanced Himawari Imager to study these plumes. We find very high values of optical thickness not observed in other operational satellite products, suggesting these plumes have been missed in previous studies.
Wenhui Zhao, Yi Huang, Steven Siems, Michael Manton, and Daniel Harrison
Atmos. Chem. Phys., 24, 5713–5736, https://doi.org/10.5194/acp-24-5713-2024, https://doi.org/10.5194/acp-24-5713-2024, 2024
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We studied how shallow clouds and rain behave over the Great Barrier Reef (GBR) using a detailed weather model. We found that the shape of the land, especially mountains, and particles in the air play big roles in influencing these clouds. Surprisingly, the sea's temperature had a smaller effect. Our research helps us understand the GBR's climate and how various factors can influence it, where the importance of the local cloud in thermal coral bleaching has recently been identified.
Francisco Lang, Steven T. Siems, Yi Huang, Tahereh Alinejadtabrizi, and Luis Ackermann
Atmos. Chem. Phys., 24, 1451–1466, https://doi.org/10.5194/acp-24-1451-2024, https://doi.org/10.5194/acp-24-1451-2024, 2024
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Marine low-level clouds play a crucial role in the Earth's energy balance, trapping heat from the surface and reflecting sunlight back into space. These clouds are distinguishable by their large-scale spatial structures, primarily characterized as hexagonal patterns with either filled (closed) or empty (open) cells. Utilizing satellite observations, these two cloud type patterns have been categorized over the Southern Ocean and North Pacific Ocean through a pattern recognition program.
Neil C. Swart, Torge Martin, Rebecca Beadling, Jia-Jia Chen, Christopher Danek, Matthew H. England, Riccardo Farneti, Stephen M. Griffies, Tore Hattermann, Judith Hauck, F. Alexander Haumann, André Jüling, Qian Li, John Marshall, Morven Muilwijk, Andrew G. Pauling, Ariaan Purich, Inga J. Smith, and Max Thomas
Geosci. Model Dev., 16, 7289–7309, https://doi.org/10.5194/gmd-16-7289-2023, https://doi.org/10.5194/gmd-16-7289-2023, 2023
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Current climate models typically do not include full representation of ice sheets. As the climate warms and the ice sheets melt, they add freshwater to the ocean. This freshwater can influence climate change, for example by causing more sea ice to form. In this paper we propose a set of experiments to test the influence of this missing meltwater from Antarctica using multiple different climate models.
Daniel Robbins, Caroline Poulsen, Steven Siems, and Simon Proud
Atmos. Meas. Tech., 15, 3031–3051, https://doi.org/10.5194/amt-15-3031-2022, https://doi.org/10.5194/amt-15-3031-2022, 2022
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A neural network (NN)-based cloud mask for a geostationary satellite instrument, AHI, is developed using collocated data and is better at not classifying thick aerosols as clouds versus the Japanese Meteorological Association and the Bureau of Meteorology masks, identifying 1.13 and 1.29 times as many non-cloud pixels than each mask, respectively. The improvement during the day likely comes from including the shortest wavelength bands from AHI in the NN mask, which the other masks do not use.
Francisco Lang, Luis Ackermann, Yi Huang, Son C. H. Truong, Steven T. Siems, and Michael J. Manton
Atmos. Chem. Phys., 22, 2135–2152, https://doi.org/10.5194/acp-22-2135-2022, https://doi.org/10.5194/acp-22-2135-2022, 2022
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Marine low-level clouds cover vast areas of the Southern Ocean, and they are essential to the Earth system energy balance. We use 3 years of satellite observations to group low-level clouds by their spatial structure using a pattern-recognizing program. We studied two primary cloud type patterns, i.e. open and closed clouds. Open clouds are uniformly distributed over the storm track, while closed clouds are most predominant in the southeastern Indian Ocean. Closed clouds exhibit a daily cycle.
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Short summary
To investigate why ERA5 (European Centre for Medium-Range Weather Forecasts Reanalysis v5) does not accurately capture the observed increase in annual precipitation at Macquarie Island during 1979 to 2023, we classify daily synoptic systems using k-means clustering. Find that the increase in mean intensity across all systems is the main contributor to the observed annual precipitation trend and the resulting discrepancy, rather than changes in the frequency. And this increase may also have a substantial impact on the freshwater fluxes over the Southern Ocean.
To investigate why ERA5 (European Centre for Medium-Range Weather Forecasts Reanalysis v5) does...
