Yi Huang

The Great Barrier Reef (GBR) is increasingly threatened by mass thermal coral bleaching events under climate change. Marine cloud brightening (MCB) has been proposed as a potential adaptation strategy to reduce thermal stress by enhancing cloud reflectivity through aerosol injection. This study evaluates the sensitivity of cloud–aerosol interactions to aerosol emission intensity and spatial configuration over the GBR using convection-permitting Weather Research and Forecasting (WRF) model simulations. A control simulation representing a non- to weakly-precipitating shallow trade-cumulus regime is compared with three MCB sensitivity experiments: a densely distributed (20 km apart), moderate emission flux scenario (EXP20), a sparsely distributed (100 km spacing), high emission flux scenario (EXP100), and an intermediate configuration (EXP40). Results show that enhanced aerosol emissions substantially increase near-surface aerosol concentrations, with dispersion strongly governed by source spacing and prevailing trade winds. The EXP20 configuration produces more homogeneous and widespread aerosol enhancements, whereas EXP100 generates localized peaks that are rapidly removed, resulting in smaller domain-mean increases despite identical total emissions. Over a 24 h period, domain-averaged cloud droplet number concentration (CDNC), optical depth, and cloud albedo exhibit strong sensitivity to aerosol loading, while cloud water path (CWP) and cloud fraction show limited responses. These findings indicate a dominant Twomey effect in this cloud regime, with only weak evidence of the Albrecht effect. Nonlinear CWP responses are noted under varying conditions of mid-level humidity, wind shear, and lower-tropospheric stability. Overall, the results highlight the importance of aerosol source configuration and background atmospheric state in shaping MCB effectiveness over the GBR.

The Great Barrier Reef (GBR) is increasingly threatened by marine heatwaves and mass coral bleaching events, with local atmospheric conditions playing a critical role in modulating sea surface temperatures and heat stress. This study examines how synoptic-to-mesoscale meteorological processes shaped cloud formation, precipitation and the ocean surface heat budget across the central GBR during the 2021–22 austral summer. Using a combination of observations, reanalysis data and high-resolution convection-permitting simulations, two representative cases are analysed: a trade wind breakdown period associated with early-summer heating and a trade wind regime linked to mid-summer cooling. The breakdown case featured enhanced convective available potential energy, deep convection, greater upper-level moisture transport and heavier rainfall, while exhibiting reduced latent heat flux owing to weaker winds. By contrast, the trade wind case was characterised by shallow clouds, dry atmospheric conditions, stronger latent cooling and minimal rainfall. Mesoscale convective systems during breakdown periods generated temporally limited but spatially extensive increases in surface winds and turbulent heat fluxes, particularly near the coast where coral reefs are concentrated. These episodes contributed to localised cooling of the ocean surface, offering temporary relief from heat stress, with this effect not being captured in coarser reanalyses. This study highlights the crucial role of synoptic-to-mesoscale atmospheric variability in influencing the surface heat budget of the GBR and demonstrates the added value of high-resolution simulations in resolving mesoscale processes relevant to reef-scale heat stress. These findings have important implications for assessing coral bleaching risk under current and future climate conditions.

Marine heatwaves and coral bleaching pose significant threats to the Great Barrier Reef (GBR), particularly during austral summer when atmospheric conditions can significantly enhance ocean surface warming. One such condition is the development of doldrums, characterised by weak winds and reduced cloud cover, which promote increased solar heating of the ocean surface. When these conditions persist, this buildup of heat can develop into marine heatwaves contributing to widespread coral bleaching. Despite these impacts, the formation and persistence of the doldrums remain poorly understood. Here, we identify doldrums events over the GBR through a K -means cluster analysis and investigate the tropical and extratropical interactions associated with their onset and maintenance. Expanding upon previous links between doldrums formation and Rossby waves, the cyclonic anomaly within the Rossby wave packet is found to disrupt the typical trade wind easterlies over the GBR through anomalous westerlies over eastern Australia. If the cyclonic anomaly propagates east quickly, the doldrums tend to cease; if the anomaly stalls, the doldrums tend to persist. These stalled Rossby wave packets are associated with repeated cyclonic Rossby wave breaking over Australia, which weakens the zonal flow and enhances blocking near New Zealand. Concurrently, favourable conditions are needed in the tropics to establish and maintain the doldrums. During longer doldrums, the slower-moving Madden–Julian Oscillation and Equatorial Rossby wave more frequently align their suppressed phases over the GBR, reinforcing anomalous westerlies to further counter the trade easterlies. Finally, Lagrangian trajectory analysis reveals that dry descending air within the doldrums typically originates in the mid-latitudes. Here, the positioning of the cyclonic anomaly or cut-off low forces the parcels to sweep across southern Australia over the dry interior before reaching the GBR. Together, these results highlight the tropical-extratropical interactions that promote the doldrums persistence over the GBR and favours the development of both marine and terrestrial heatwaves.

Marine heatwaves and coral bleaching pose significant threats to the Great Barrier Reef (GBR), particularly during austral summer when atmospheric conditions can significantly enhance ocean surface warming. One such condition is the development of doldrums, characterised by weak winds and reduced cloud cover, which promote increased solar heating of the ocean surface. When these conditions persist, this buildup of heat can develop into marine heatwaves contributing to widespread coral bleaching. Despite these impacts, the formation and persistence of the doldrums remain poorly understood. Here, we identify doldrum events over the GBR through a K-means cluster analysis and investigate the tropical and extratropical interactions associated with their onset and maintenance. We show that doldrums formation is linked to the passage of a Rossby wave packet, in which a cyclonic anomaly and anomalous westerlies over eastern Australia disrupt the typical trade wind easterlies over the GBR. If the cyclonic anomaly propagates east quickly, the doldrums tend to cease; if the anomaly stalls, the doldrums tend to persist. These stalled Rossby wave packets are associated with repeated cyclonic Rossby wave breaking over Australia, which weakens the zonal flow and enhances blocking near New Zealand. Concurrently, favourable conditions are needed in the tropics to establish and maintain the doldrums. During longer doldrums, the slower-moving Madden-Julian Oscillation and Equatorial Rossby wave more frequently align their suppressed phases over the GBR, reinforcing anomalous westerlies to further counter the trade easterlies. Finally, Lagrangian trajectory analysis reveals that dry descending air within the doldrums typically originates in the mid-latitudes. Here, the positioning of the cyclonic anomaly or cut‑off low forces the parcels to sweep across southern Australia over the dry interior before reaching the GBR. Together, these results highlight the tropical-extratropical interactions that promote the doldrums persistence over the GBR and favours the development of both marine and terrestrial heatwaves.

Marine heatwaves and coral bleaching pose significant threats to the Great Barrier Reef (GBR), particularly during austral summer when atmospheric conditions can significantly enhance ocean surface warming. One such condition is the development of doldrums, characterised by weak winds and reduced cloud cover, which promote increased solar heating of the ocean surface. When these conditions persist, this buildup of heat can develop into marine heatwaves contributing to widespread coral bleaching. Despite these impacts, the formation and persistence of the doldrums remain poorly understood. Here, we identify doldrum events over the GBR through a K-means cluster analysis and investigate the tropical and extratropical interactions associated with their onset and maintenance. We show that doldrums formation is linked to the passage of a Rossby wave packet, in which a cyclonic anomaly and anomalous westerlies over eastern Australia disrupt the typical trade wind easterlies over the GBR. If the cyclonic anomaly propagates east quickly, the doldrums tend to cease; if the anomaly stalls, the doldrums tend to persist. These stalled Rossby wave packets are associated with repeated cyclonic Rossby wave breaking over Australia, which weakens the zonal flow and enhances blocking near New Zealand. Concurrently, favourable conditions are needed in the tropics to establish and maintain the doldrums. During longer doldrums, the slower-moving Madden-Julian Oscillation and Equatorial Rossby wave more frequently align their suppressed phases over the GBR, reinforcing anomalous westerlies to further counter the trade easterlies. Finally, Lagrangian trajectory analysis reveals that dry descending air within the doldrums typically originates in the mid-latitudes. Here, the positioning of the cyclonic anomaly or cut‑off low forces the parcels to sweep across southern Australia over the dry interior before reaching the GBR. Together, these results highlight the tropical-extratropical interactions that promote the doldrums persistence over the GBR and favours the development of both marine and terrestrial heatwaves.

Mass coral bleaching events are becoming increasingly frequent over the Great Barrier Reef (GBR), posing a critical risk to Australia's marine ecosystems and the broader global ocean environment. These events are primarily driven by anomalously warm water temperatures, but their severity is strongly influenced by local cloud cover, which controls the amount of solar radiation reaching the ocean surface (including ultra-violet radiation which exacerbates bleaching). This study presents a characterization of the cloud and rainfall diurnal cycles over north-east Queensland during the coral bleaching season, providing a foundational step to untangling the complex relationships between clouds, rainfall, local-scale processes and the surface energy budget for this climate-sensitive region. Leveraging high-resolution Himawari-8 satellite brightness temperature data, C-band radar observations, and BARRA-R2 regional reanalysis, a multi-year analysis is conducted across three representative zones: coastal land, coastal ocean and open ocean. Results show that diurnal cycles vary distinctly by region and are strongly modulated by prevailing wind regimes. In general, westerly regimes are associated with clear skies and stronger daytime heating over the coastal ocean with enhanced convection over coastal land. In contrast, the frequently observed southeasterlies lead to relatively weaker development over the land and ocean. Cloud and rainfall maxima exhibit out-of-phase behavior between land and ocean, with rainfall often preceding cold cloud tops, indicative that cold brightness temperatures frequently correspond to decaying anvils rather than active convection. Latitudinal and topographic differences contribute to more intense convection near Cairns than Townsville. Variations in inland versus offshore propagation speeds further highlight regional complexity. Our findings emphasize the need for high-resolution simulations to better understand the convection initiation and propagation processes that shape cloud cover and rainfall variability over the GBR during the coral bleaching season, when cloud-radiation interactions may influence reef heat stress.

The orographic precipitation enhancement (OPE) generated within wintertime post‐frontal air masses is a prominent climate feature of Tasmania. This study investigates a passage of a cold sector of a mid‐latitude cyclone over the Southern Ocean (SO) and Western Tasmania (WTAS) observed from 2100 UTC 11 July to 0300 UTC 13 July. The in situ and remote sensing observations have been used to study clouds and precipitation over the SO and WTAS. Those observations include Optical Particle Size Velocity disdrometers and Micro Rain Radars implemented during a winter field campaign implemented in 2019, 27 rain gauges operated by Hydro Tasmania, C‐band weather radar and satellite‐based observations. ERA5 reanalysis was used to analyze the synoptic meteorology and thermodynamic conditions. Deep convection reaching heights of 8 km was observed over the SO and Tasmania and was triggered by a post‐frontal trough. The microphysical properties of these deep convective clouds were substantially different from those for the shallow open mesoscale cellular convection, which is commonly observed over the SO. The deep convective clouds and OPE produced heavy precipitation exceeding 55 mm over WTAS according to in situ observations during the post‐frontal period (over 30 hr). The GPM‐IMERG satellite‐based precipitation product captured the spatial pattern of the OPE over WTAS though rain gauge calibration induced overestimation of heavy precipitation at some sites. The analysis of C‐band radar observations suggests that orographic convection invigoration and convective‐to‐stratiform transition mechanisms produced OPE over WTAS.

The Great Barrier Reef (GBR) is increasingly threatened by mass thermal coral bleaching events under climate change. Marine cloud brightening (MCB) has been proposed as a potential adaptation strategy to reduce thermal stress by enhancing cloud reflectivity through aerosol injection. This study evaluates the sensitivity of cloud–aerosol interactions to aerosol emission intensity and spatial configuration over the GBR using convection-permitting Weather Research and Forecasting (WRF) model simulations. A control simulation representing a non- to weakly-precipitating shallow trade-cumulus regime is compared with three MCB sensitivity experiments: a densely distributed (20 km apart), moderate-intensity emission scenario (EXP20), a sparsely distributed (100 km spacing), high-intensity scenario (EXP100), and an intermediate configuration (EXP40). Results show that enhanced aerosol emissions substantially increase near-surface aerosol concentrations, with dispersion strongly governed by source spacing and prevailing trade winds. The EXP20 configuration produces more homogeneous and widespread aerosol enhancements, whereas EXP100 generates localized peaks that are rapidly scavenged, resulting in smaller domain-mean increases despite identical total emissions. Over a 24-hour period, domain-averaged cloud droplet number concentration (CDNC), optical depth, and cloud albedo exhibit strong sensitivity to aerosol loading, while cloud water path (CWP) and cloud fraction show limited responses. These findings indicate a dominant Twomey effect in this cloud regime, with only weak evidence of the Albrecht effect. Nonlinear CWP responses are noted under varying conditions of mid-level humidity, wind shear, and lower-tropospheric stability. Overall, the results highlight the importance of aerosol source configuration and background atmospheric state in shaping MCB effectiveness over the GBR.

The Great Barrier Reef (GBR) is increasingly threatened by mass thermal coral bleaching events under climate change. Marine cloud brightening (MCB) has been proposed as a potential adaptation strategy to reduce thermal stress by enhancing cloud reflectivity through aerosol injection. This study evaluates the sensitivity of cloud–aerosol interactions to aerosol emission intensity and spatial configuration over the GBR using convection-permitting Weather Research and Forecasting (WRF) model simulations. A control simulation representing a non- to weakly-precipitating shallow trade-cumulus regime is compared with three MCB sensitivity experiments: a densely distributed (20 km apart), moderate-intensity emission scenario (EXP20), a sparsely distributed (100 km spacing), high-intensity scenario (EXP100), and an intermediate configuration (EXP40). Results show that enhanced aerosol emissions substantially increase near-surface aerosol concentrations, with dispersion strongly governed by source spacing and prevailing trade winds. The EXP20 configuration produces more homogeneous and widespread aerosol enhancements, whereas EXP100 generates localized peaks that are rapidly scavenged, resulting in smaller domain-mean increases despite identical total emissions. Over a 24-hour period, domain-averaged cloud droplet number concentration (CDNC), optical depth, and cloud albedo exhibit strong sensitivity to aerosol loading, while cloud water path (CWP) and cloud fraction show limited responses. These findings indicate a dominant Twomey effect in this cloud regime, with only weak evidence of the Albrecht effect. Nonlinear CWP responses are noted under varying conditions of mid-level humidity, wind shear, and lower-tropospheric stability. Overall, the results highlight the importance of aerosol source configuration and background atmospheric state in shaping MCB effectiveness over the GBR.

The Great Barrier Reef (GBR) is increasingly threatened by mass thermal coral bleaching events under climate change. Marine cloud brightening (MCB) has been proposed as a potential adaptation strategy to reduce thermal stress by enhancing cloud reflectivity through aerosol injection. This study evaluates the sensitivity of cloud–aerosol interactions to aerosol emission intensity and spatial configuration over the GBR using convection-permitting Weather Research and Forecasting (WRF) model simulations. A control simulation representing a non- to weakly-precipitating shallow trade-cumulus regime is compared with three MCB sensitivity experiments: a densely distributed (20 km apart), moderate-intensity emission scenario (EXP20), a sparsely distributed (100 km spacing), high-intensity scenario (EXP100), and an intermediate configuration (EXP40). Results show that enhanced aerosol emissions substantially increase near-surface aerosol concentrations, with dispersion strongly governed by source spacing and prevailing trade winds. The EXP20 configuration produces more homogeneous and widespread aerosol enhancements, whereas EXP100 generates localized peaks that are rapidly scavenged, resulting in smaller domain-mean increases despite identical total emissions. Over a 24-hour period, domain-averaged cloud droplet number concentration (CDNC), optical depth, and cloud albedo exhibit strong sensitivity to aerosol loading, while cloud water path (CWP) and cloud fraction show limited responses. These findings indicate a dominant Twomey effect in this cloud regime, with only weak evidence of the Albrecht effect. Nonlinear CWP responses are noted under varying conditions of mid-level humidity, wind shear, and lower-tropospheric stability. Overall, the results highlight the importance of aerosol source configuration and background atmospheric state in shaping MCB effectiveness over the GBR.