School of Earth Sciences - Research Publications
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ItemNo Preview AvailableHimawari-8 GeoCat 1.0.3 Australian Domain Level 1 v1.0( 2021-03-15)
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ItemCoral-reef-derived dimethyl sulfide and the climatic impact of the loss of coral reefs(COPERNICUS GESELLSCHAFT MBH, 2021-04-20)Abstract. Dimethyl sulfide (DMS) is a naturally occurring aerosol precursor gas which plays an important role in the global sulfur budget, aerosol formation and climate. While DMS is produced predominantly by phytoplankton, recent observational literature has suggested that corals and their symbionts produce a comparable amount of DMS, which is unaccounted for in models. It has further been hypothesised that the coral reef source of DMS may modulate regional climate. This hypothesis presents a particular concern given the current threat to coral reefs under anthropogenic climate change. In this paper, a global climate model with online chemistry and aerosol is used to explore the influence of coral-reef-derived DMS on atmospheric composition and climate. A simple representation of coral-reef-derived DMS is developed and added to a common DMS surface water climatology, resulting in an additional flux of 0.3 Tg yr−1 S, or 1.7 % of the global sulfur flux from DMS. By comparing the differences between both nudged and free-running ensemble simulations with and without coral-reef-derived DMS, the influence of coral-reef-derived DMS on regional climate is quantified. In the Maritime Continent–Australian region, where the highest density of coral reefs exists, a small decrease in nucleation- and Aitken-mode aerosol number concentration and mass is found when coral reef DMS emissions are removed from the system. However, these small responses are found to have no robust effect on regional climate via direct and indirect aerosol effects. This work emphasises the complexities of the aerosol–climate system, and the limitations of current modelling capabilities are highlighted, in particular surrounding convective responses to changes in aerosol. In conclusion, we find no robust evidence that coral-reef-derived DMS influences global and regional climate.
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ItemExtreme rainfall in New Zealand and its association with Atmospheric Rivers(Institute of Physics (IoP), 2021-04-01)Atmospheric rivers (ARs) are narrow and elongated regions of enhanced horizontal water vapour transport. Considerable research on understanding Northern Hemisphere ARs and their relationship with extreme precipitation has shown that ARs have a strong association with heavy rainfall and flooding. While there has been very little work on ARs in the Southern Hemisphere, global climatologies suggest that ARs are equally as common in both hemispheres. New Zealand in particular is located in a region of high AR frequency. This study aims to test the hypothesis that ARs play a significant role in heavy precipitation and flooding events in New Zealand. We used a recently developed AR identification method and daily station data across New Zealand to test for the concurrence of ARs and extreme rainfall. We found that, at each of the eleven stations analysed, at least seven to all ten of the top ten heaviest precipitation days between 1980 and 2018 were associated with AR conditions. Nine of the ten most damaging floods in New Zealand between 2007 and 2017 occurred during AR events. These results have important implications for understanding extreme rainfall in New Zealand, and ultimately for predicting some of the most hazardous events in the region. This work also highlights that more research on ARs in New Zealand is needed.
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ItemDoes Lower‐Stratospheric Shear Influence the Mesoscale Organization of Convection?(American Geophysical Union (AGU), 2021-02-16)Organized mesoscale convection is important for many atmospheric phenomena and hazards, however the understanding of its governing mechanisms is incomplete. Theories explaining mesoscale organization rely on the interaction between convection outflows and lower‐tropospheric wind shear. Here a new mechanism is presented, where lower‐stratospheric wind shear is shown to influence mesoscale organization. The mechanism is linked to coupling between convection and gravity waves, with the stratosphere playing a role in shaping the tropospheric wave spectrum. The key result is that lower‐stratospheric shear creates a preference for organized systems propagating in the same direction as the shear vector by weakening the systems propagating in the opposite direction to the shear. This result has important implications for stratosphere‐troposphere interactions, numerical modeling, and understanding of convective organization in general.