School of Geography, Earth and Atmospheric Sciences - Research Publications

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Long-Term Observational Characteristics of Different Severe Convective Wind Types around Australia

Brown, A ; Dowdy, A ; Lane, TP ; Hitchcock, S (AMER METEOROLOGICAL SOC, 2023-10)

Abstract Regional understanding of severe surface winds produced by convective processes [severe convective winds (SCWs)] is important for decision-making in several areas of society, including weather forecasting and engineering design. Meteorological studies have demonstrated that SCWs can occur due to a number of different mesoscale and microscale processes, in a range of large-scale atmospheric environments. However, long-term observational studies of SCW characteristics often have not considered this diversity in physical processes, particularly in Australia. Here, a statistical clustering method is used to separate a large dataset of SCW events, measured by automatic weather stations around Australia, into three types, associated with strong background wind, steep lapse rate, and high moisture environments. These different types of SCWs are shown to have different seasonal and spatial variations in their occurrence, as well as different measured wind gust, lightning, and parent-storm characteristics. In addition, various convective diagnostics are tested in their ability to discriminate between measured SCW events and nonsevere events, with significant variations in skill between event types. Differences in environmental conditions and wind gust characteristics between event types suggests potentially different physical processes for SCW production. These findings are intended to improve regional understanding of severe wind characteristics, as well as environmental prediction of SCWs in weather and climate applications, by considering different event types. Significance Statement The purpose of this study is to improve regional understanding of different types of severe wind events in Australia, specifically those associated with atmospheric convection. We did this by constructing a dataset of 413 severe convective wind events, using weather station and radar data within 20 regions around Australia. We then split those events into three different types, based on the environmental conditions that they occur within. We found that each event type tends to occur at different times of the year and in different regions, while also having different wind gust and lightning characteristics. In addition, the atmospheric conditions that are helpful for prediction of severe wind events differs between each type. These results are intended to be useful for prediction of severe wind events associated with convection and assessing their variability, characteristics, and impacts, in both weather forecasting and climate analysis.
Two Quasi-Linear Convective Systems, Their Mesoscale Structure and Moisture Sources

Hitchcock, SM ; Lane, TP (AMER METEOROLOGICAL SOC, 2023-03-01)

Abstract Over half of the total rainfall and more than 70% of heavy and extreme rainfall in the Melbourne, Australia, region occurs on days with linearly organized precipitation. These systems are typically convective in nature and frequently associated with cold fronts. It is useful to understand the processes that support extreme rainfall in organized convection, for prediction of both near-term and future extreme rainfall, and the topography and climate of Melbourne are different from many of the regions where QLCSs have been studied more extensively (e.g., the U. S. Great Plains region). On both 7 and 8 December 2010, a QLCS passed through the Melbourne region. Both QLCSs resembled classic systems on radar, but heavy rainfall was much more widespread on the second day. The goals of this work are to 1) understand the processes that drive these seemingly similar QLCSs; 2) explore the relationship between the convective inflow layer and moisture sources; and 3) to better understand the characteristics of rain bearing systems in the Melbourne region, which have received little attention to date. A convection-permitting WRF-ARW simulation captures both events. The mesoscale structure is different in each case, but generally is explainable by the existing theory. The development of a mesoscale downdraft, along with more moisture (and CAPE) over a deeper layer, contributed to higher rainfall totals on the second day. Low-level moisture in the QLCS region comes from the east, and parcel trajectories become increasingly westerly with height. On the second day some parcels originate in the tropics; these tend to have the most moisture. Significance Statement A lot of the rain that falls in Melbourne, Australia, occurs in storms that are grouped or “organized” in the shape of a line. Many studies have looked at how lines of storms work in other places in the world. In southeast Australia, only one study in the 1980s looked at observations of a line of storms. Since then, our understanding of storms and our ability to use computer models to simulate them has improved considerably. In this study we simulate two lines of storms that happened two days in a row. We found that even though they looked similar on weather radar, they had many differences including how air flows through the storm, the role of rain-cooled air, and where moisture comes from.
Do water-saving policies improve water-use technical efficiency? Evidence from the water-receiving cities of China's South-North Water Transfer Project

Sheng, J ; Webber, M (ROUTLEDGE JOURNALS, TAYLOR & FRANCIS LTD, 2023-01-01)
Paternalism to empowerment: all in the eye of the beholder?

Carney, T ; Bigby, C ; Then, S-N ; Smith, E ; Wiesel, I ; Douglas, J (ROUTLEDGE JOURNALS, TAYLOR & FRANCIS LTD, 2023-03-16)
Region power for mobilities research

Bissell, D ; Birtchnell, T ; Duffy, M ; Fozdar, F ; Iaquinto, BL ; Radford, D ; Rickards, L (ROUTLEDGE JOURNALS, TAYLOR & FRANCIS LTD, 2023-07-03)
Communicating the link between climate change and extreme rain events

King, ADD ; Reid, KJJ ; Saunders, KRR (NATURE PORTFOLIO, 2023-07-01)
Reducing personal climate anxiety is key to adaptation

Mortreux, C ; Barnett, J ; Jarillo, S ; Greenaway, KH (NATURE PORTFOLIO, 2023-07-01)
Using Machine Learning to Cut the Cost of Dynamical Downscaling

Hobeichi, S ; Nishant, N ; Shao, Y ; Abramowitz, G ; Pitman, A ; Sherwood, S ; Bishop, C ; Green, S (AMER GEOPHYSICAL UNION, 2023-03-01)

Abstract Global climate models (GCMs) are commonly downscaled to understand future local climate change. The high computational cost of regional climate models (RCMs) limits how many GCMs can be dynamically downscaled, restricting uncertainty assessment. While statistical downscaling is cheaper, its validity in a changing climate is unclear. We combine these approaches to build an emulator leveraging the merits of dynamical and statistical downscaling. A machine learning model is developed for each coarse grid cell to predict fine grid variables, using coarse‐scale climate predictors with fine grid land characteristics. Two RCM emulators, one Multilayer Perceptron (MLP) and one Multiple Linear Regression error‐reduced with Random Forest (MLR‐RF), are developed to downscale daily evapotranspiration from 12.5 km (coarse‐scale) to 1.5 km (fine‐scale). Out‐of‐sample tests for the MLP and MLR‐RF achieve Kling‐Gupta‐Efficiency of 0.86 and 0.83, correlation of 0.89 and 0.86, and coefficient of determination (R2) of 0.78 and 0.75, with a relative bias of −6% to 5% and −5% to 4%, respectively. Using histogram match for spatial efficiency, both emulators achieve a median score of ∼0.77. This is generally better than a common statistical downscaling method in a range of metrics. Additionally, through “spatial transitivity,” we can downscale GCMs for new regions at negligible cost and only minor performance loss. The framework offers a cheap and quick way to downscale large ensembles of GCMs. This could enable high‐resolution climate projections from a larger number of global models, enabling uncertainty quantification, and so better support for resilience and adaptation planning.
The Diurnal Cycle of Rainfall and Deep Convective Clouds Around Sumatra and the Associated MJO-Induced Variability During Austral Summer in Himawari-8

Lopez-Bravo, C ; Vincent, CL ; Huang, Y ; Lane, TP (American Geophysical Union (AGU), 2023-11-27)

Abstract The effects of the diurnal cycle and large‐scale atmospheric disturbances dominate rainfall and cloud variability in the Maritime Continent. This study examines the modulation of the Austral Summer diurnal cycle by the Madden–Julian Oscillation (MJO) using cloud populations through precipitation and deep convective cloud derived from satellite measurements. Using Rainfall Potential Areas from Himawari‐8 Advanced Himawari Imager as a proxy for deep convection, our analysis shows that convective clouds are present ∼55% of the time over land in Sumatra during the afternoon and night. Cloud signatures reveal semi‐diurnal structures of deep convective clouds off the West Coast of Sumatra. In contrast, the East Coast exhibits explicit sea‐ward propagation patterns of deep convective controlled by the coastal effects around the Strait of Malacca and Java Sea, together with the influence of synchronized diurnal forcing between islands. We show that the MJO drives the enhanced convective phases, changing the cloud top type distribution, moisture convergence, and moisture transport over the equatorial Indian Ocean. The cold cloud area also increases during the MJO active phases, which is linked to frequent deep convective cloud development near the mountain ranges of Sumatra and the adjacent ocean. The analyses of cloud variations based on the rainfall potential areas and cloud top type provide evidence of the effects of convective processes on the diurnal cycle of ice and water vapor distribution in the troposphere.
Persistent late Tonian shallow marine anoxia and euxinia

Stacey, J ; Hood, AVS ; Wallace, MW (Elsevier BV, 2023-10-01)

School of Geography, Earth and Atmospheric Sciences - Research Publications

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