Articles | Volume 6, issue 4
https://doi.org/10.5194/wcd-6-1797-2025
© 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-6-1797-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
10 Dec 2025
Research article |
| 10 Dec 2025
| 10 Dec 2025
The impact of synoptic meteorology on observed surface heat fluxes over the Southern Ocean
School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria, Australia
Australian Research Council's Securing Antarctica's Environmental Future (SAEF), Melbourne, Victoria, Australia
Tahereh Alinejadtabrizi
School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria, Australia
Steven Siems
School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria, Australia
Australian Research Council's Securing Antarctica's Environmental Future (SAEF), Melbourne, Victoria, Australia
Peter T. May
School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria, Australia
Haifeng Zhang
Bureau of Meteorology, Melbourne, Victoria, Australia
Eric Schulz
Bureau of Meteorology, Melbourne, Victoria, Australia
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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
This preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).
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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.
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.
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
This preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).
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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.
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.
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.
Zhaoyang Kong, Andrew T. Prata, Peter T. May, Ariaan Purich, Yi Huang, and Steven T. Siems
Weather Clim. Dynam., 6, 1643–1660, https://doi.org/10.5194/wcd-6-1643-2025, https://doi.org/10.5194/wcd-6-1643-2025, 2025
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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.
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.
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.
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
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.
Using 14 years of observations from mooring, we reported that cold air advection creates intense...
