Articles | Volume 7, issue 4
https://doi.org/10.5194/wcd-7-1977-2026
© Author(s) 2026. 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-7-1977-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
13 Oct 2026
Research article |
| 13 Oct 2026
| 13 Oct 2026
The development and persistence of doldrums over the Great Barrier Reef
Lara S. Richards
CORRESPONDING AUTHOR
School of Earth, Atmosphere & Environment, Monash University, Clayton, Australia
The Australian Research Council Centre of Excellence for the Weather of the 21st Century, Melbourne, Australia
National Centre for Atmospheric Science, University of Reading, Reading, United Kingdom
School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Melbourne, Australia
The Australian Research Council Centre of Excellence for the Weather of the 21st Century, Melbourne, Australia
Michael A. Barnes
School of Earth, Atmosphere & Environment, Monash University, Clayton, Australia
The Australian Research Council Centre of Excellence for the Weather of the 21st Century, Melbourne, Australia
Department of Geography, Geoinformatics & Meteorology, University of Pretoria, Pretoria, South Africa
Chenhui Jin
School of Earth, Atmosphere & Environment, Monash University, Clayton, Australia
The Australian Research Council Centre of Excellence for the Weather of the 21st Century, Melbourne, Australia
Fadhlil R. Muhammad
School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Melbourne, Australia
The Australian Research Council Centre of Excellence for the Weather of the 21st Century, Melbourne, Australia
Daniel P. Harrison
National Marine Science Centre, Southern Cross University, Coffs Harbour, Australia
Steven T. Siems
School of Earth, Atmosphere & Environment, Monash University, Clayton, Australia
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Juha Sulo, Magdalena Okuljar, Joel Alroe, Zijun Li, Eva Johanna Horchler, Luke Cravigan, Branka Miljevic, Luke Harrison, Daniel Harrison, and Zoran Ristovski
Aerosol Research, 4, 413–427, https://doi.org/10.5194/ar-4-413-2026, https://doi.org/10.5194/ar-4-413-2026, 2026
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The Great Barrier Reef is the world’s largest coral reef system, and the air above it plays a role in cloud formation. Using direct measurements taken over several years, this study shows that although the reef has low aerosol concentrations, air that passes directly over coral reefs contains more very small particles, providing the first direct evidence that reefs add particles to the atmosphere. These locally produced particles make a measurable contribution to cloud formation over the reef.
Chenhui Jin, Elizabeth A. Ritchie, Michael A. Barnes, and Neil J. Holbrook
EGUsphere, https://doi.org/10.5194/egusphere-2026-5018, https://doi.org/10.5194/egusphere-2026-5018, 2026
This preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).
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This study investigates how the extratropical transition (ET) of tropical cyclones influences downstream weather in the Southern Hemisphere. Two main ET downstream developments are identified: a propagating Rossby wave train along a strong, straight jet, and a more localised downstream ridge associated with a weaker, poleward-oriented jet. The strong ET events in the southwest Indian Ocean can increase the occurrence of high-impact weather over Australia.
Anna Kuhn, Chenhui Jin, Elizabeth Ritchie, and Michael Armand Sprenger
EGUsphere, https://doi.org/10.5194/egusphere-2026-4836, https://doi.org/10.5194/egusphere-2026-4836, 2026
This preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).
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We apply a clustering approach to analyze winter jet stream variability over Australia, defining five jet configurations. We find high variability, especially in the longitudinal jet maximum. Patterns of vertical motion show the strongest ascent south of the jet maximum, coinciding with enhanced precipitation. Extreme precipitation events for six Australian capital cities are linked to either a strong or weakened jet stream, highlighting the important role of the jet in driving those events.
Magdalena Okuljar, Juha Sulo, Joel Alroe, Zijun Li, Branka Miljevic, Daniel Harrison, and Zoran Ristovski
EGUsphere, https://doi.org/10.5194/egusphere-2026-4869, https://doi.org/10.5194/egusphere-2026-4869, 2026
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The Great Barrier Reef is the largest coral reef system globally, yet the extent to which it contributes to local atmospheric particle loading remains poorly understood. This work focuses on particle formation processes observed during a six-week measurement campaign. Our results show that the reef ecosystem can influence local aerosol formation processes, with implications for regional cloud formation and climate feedbacks in marine ecosystems.
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
Atmos. Chem. Phys., 26, 11583–11604, https://doi.org/10.5194/acp-26-11583-2026, https://doi.org/10.5194/acp-26-11583-2026, 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.
A. V. Sreenath, Peter T. May, Steven Siems, Heather Corden, and Alexis Berne
EGUsphere, https://doi.org/10.5194/egusphere-2026-4159, https://doi.org/10.5194/egusphere-2026-4159, 2026
This preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).
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We investigated how synoptic weather regimes control cloud growth and surface precipitation at Dumont d’Urville, East Antarctica. Multi-instrument observations show that synoptic forcing determines hydrometeor growth and precipitation formation aloft, while boundary-layer conditions, including local downslope flow and near-surface moisture, control how much precipitation reaches the surface.
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.
Chenhui Jin, Elizabeth A. Ritchie, and Neil J. Holbrook
Weather Clim. Dynam., 7, 1285–1306, https://doi.org/10.5194/wcd-7-1285-2026, https://doi.org/10.5194/wcd-7-1285-2026, 2026
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Tropical cyclones that move into the midlatitudes become extratropical cyclones, so-called extratropical transition. In this study, we detected transition events in the Southern Hemisphere based on the model data. We found that weather patterns during the transition are different from case to case. In some cases, strong tropical cyclones interact with the midlatitude flow and lead to great changes in weather nearby.
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.
Rebecca L. Jackson, Matthew T. Woodhouse, Mark Baird, Clothilde Langlais, Mathieu Mongin, Anthony Jones, Daniel Partridge, Luke Harrison, Johanna Horchler, Joel Alroe, Luke Cravigan, Zoran Ristovski, and Daniel P. Harrison
EGUsphere, https://doi.org/10.5194/egusphere-2026-2761, https://doi.org/10.5194/egusphere-2026-2761, 2026
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ACCESS-EMS-GBR is a regional coupled atmosphere-ocean model of the Great Barrier Reef. It simulates aerosol and cloud processes in the atmosphere, plus hydrodynamics, biogeochemistry and ecological processes in the marine environment. Developed to assess the effects of Marine Cloud Brightening on coral bleaching, it is the first regional model able to simulate how aerosol emissions affect clouds, radiation and the underlying reef ecosystem and is ideal for a range of atmosphere-ocean studies.
Linyuan Sun, Andréa S. Taschetto, Shayne McGregor, Lisa V. Alexander, and Chenhui Jin
EGUsphere, https://doi.org/10.5194/egusphere-2026-3344, https://doi.org/10.5194/egusphere-2026-3344, 2026
This preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).
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The El Niño-Southern Oscillation strongly affects Australia’s rainfall, but its impacts on Australian extratropical cyclones are difficult to detect. By focusing on days when ENSO-related teleconnection patterns were established, we identified clearer changes in cyclone activity over the Tasman Sea, with more frequent cyclones during La Niña and fewer during El Niño. These results provide new insights into how large-scale climate modes influence regional weather systems.
Johannes Kainz, Daniel P. Harrison, and Fabian Hoffmann
Atmos. Chem. Phys., 26, 9443–9451, https://doi.org/10.5194/acp-26-9443-2026, https://doi.org/10.5194/acp-26-9443-2026, 2026
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Marine Cloud Brightening (MCB) aims to counter global warming. It suggests to increase cloud reflectance by spraying aerosols from which additional cloud droplets can form. We demonstrate that MCB can be applied to cumulus clouds. The impact of aerosol particles released by a single aerosol sprayer using simulations is analyzed. The study draws conclusions on the optimal placement height of the sprayer to optimize aerosol transport, the ability to form new cloud droplets, and the area affected.
Michael A. Barnes, James S. Risbey, Teresa J. Parker, Nicholas Earl-Jones, Carly Tozer, and Didier P. Monselesan
EGUsphere, https://doi.org/10.5194/egusphere-2026-3141, https://doi.org/10.5194/egusphere-2026-3141, 2026
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The physical interpretation of the Southern Annular Mode (SAM) has been questioned in recent years. Here we show that the SAM can be interpreted through the diagnosis of synoptic-scale weather systems. In particular, the SAM is described here by the sum of the characteristics of Rossby wave breaking zones across the Southern Ocean. These differences produce local differences in the frequency of mid-latitudes cyclones and jets which the SAM is assumed to alter hemispherically.
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.
Ramon Campos Braga, Daniel Harrison, Manfred Wendisch, and Rachel Albrecht
EGUsphere, https://doi.org/10.5194/egusphere-2026-795, https://doi.org/10.5194/egusphere-2026-795, 2026
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We introduce a new thermodynamic method to quantify water vapor supersaturation (Sv) at warm cloud bases by describing the ascent of a cloudy air parcel as a reversible cloud-adiabatic process. This approach enables the calculation of cloud-base droplet number concentration spectra from in situ airborne measurements without reliance on prescribed updraft velocities or empirical parameterizations. The method is validated using CCN measurements from airborne observations over the Amazon Basin.
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.
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.
Robert G. Ryan, Lilani Toms-Hardman, Alexander Smirnov, Daniel P. Harrison, and Robyn Schofield
Atmos. Chem. Phys., 25, 11183–11197, https://doi.org/10.5194/acp-25-11183-2025, https://doi.org/10.5194/acp-25-11183-2025, 2025
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Measurements of aerosol vertical distribution are key for understanding how they interact with clouds and sunlight. Such measurements are currently lacking at the Great Barrier Reef, limiting our ability to validate climate models in this sensitive, ecologically rich environment. Here we use a range of techniques to quantify the vertical variation of aerosols above the Great Barrier Reef for the first time, using the comparison of techniques to also infer aerosol spatial variation.
E. Johanna Horchler, Joel Alroe, Luke Harrison, Luke Cravigan, Daniel P. Harrison, and Zoran D. Ristovski
Atmos. Chem. Phys., 25, 10075–10087, https://doi.org/10.5194/acp-25-10075-2025, https://doi.org/10.5194/acp-25-10075-2025, 2025
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Aerosols play a role in global climate by interacting with incoming solar radiation and by taking up water vapour from the atmosphere to form clouds. Enhancing local-scale cloud cover can reduce sea surface temperatures. Coral bleaching events have increased in the Great Barrier Reef (GBR) as sea surface temperatures have risen. Our study found that the number of aerosols and the cloud-forming ability over the GBR increased if the aerosols were transported from inland Australia rather than the 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.
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.
Michael A. Barnes, Thando Ndarana, Michael Sprenger, and Willem A. Landman
Weather Clim. Dynam., 3, 1291–1309, https://doi.org/10.5194/wcd-3-1291-2022, https://doi.org/10.5194/wcd-3-1291-2022, 2022
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Stratospheric air can intrude into the troposphere and is associated with cyclonic development throughout the atmosphere. Through a highly idealized systematic approach, the effect that different intrusion characteristics have on surface cyclogenetic forcing is investigated. The proximity of stratospheric intrusions to the surface is shown to be the main factor in surface cyclogenetic forcing, whilst its width is an additional contributing factor.
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
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 how the stalling of these weather systems prolongs the doldrums over the Great Barrier Reef.
The doldrums are regions of light winds and relatively clear skies found in the tropics. They...
