Articles | Volume 7, issue 1
https://doi.org/10.5194/wcd-7-109-2026
© 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-7-109-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
16 Jan 2026
Research article |
| 16 Jan 2026
| 16 Jan 2026
Trade wind regimes during the Great Barrier Reef coral bleaching season
Lara S. Richards
CORRESPONDING AUTHOR
School of Earth, Atmosphere and Environment, Monash University, Melbourne, Australia
The Australian Research Council Centre of Excellence for the Weather of the 21st Century, Melbourne, Australia
Steven T. Siems
School of Earth, Atmosphere and Environment, Monash University, Melbourne, Australia
The Australian Research Council Centre of Excellence for the Weather of the 21st Century, Melbourne, Australia
School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Melbourne, Australia
Daniel P. Harrison
National Marine Science Centre, Southern Cross University, Coffs Harbour, Australia
Wenhui Zhao
School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Melbourne, Australia
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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.
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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.
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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.
Wenhui Zhao, Yi Huang, Steven Siems, and Daniel Harrison
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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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Alanah Chapman, Yi Huang, and Claire Vincent
EGUsphere, https://doi.org/10.5194/egusphere-2026-1019, https://doi.org/10.5194/egusphere-2026-1019, 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.
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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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.
Juha Sulo, Magdalena Okuljar, Joel Alroe, Zijun Li, Eva Johanna Horchler, Luke Cravigan, Branka Miljevic, Luke Harrison, Daniel Harrison, and Zoran Ristovski
Aerosol Research Discuss., https://doi.org/10.5194/ar-2026-9, https://doi.org/10.5194/ar-2026-9, 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.
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.
Johannes Kainz, Daniel Patrick Harrison, and Fabian Hoffmann
EGUsphere, https://doi.org/10.5194/egusphere-2025-5575, https://doi.org/10.5194/egusphere-2025-5575, 2025
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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.
Robert G. Ryan, Lilani Toms-Hardman, Alexander Smirnov, Daniel P. Harrison, and Robyn Schofield
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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.
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
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.
By studying the variability of the trade winds during the Great Barrier Reef coral bleaching...
