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Atmospheric science

AOES PhD Students Awarded Research Fellowships


PhD students David Benson and Rachel Gaal

George Mason University awarded 2021 summer research fellowships to two AOES Climate Dynamics doctoral students, David Benson and Rachel Gaal, in order to provide financial support for work on their dissertations.  Their work centers on the effect of soil moisture on two very different weather phenomena, heat waves and rain storms. 

Benson schematic land-air interactions

Heatwaves are extreme events that pose a danger to lives and agriculture, and which are influenced by soil conditions. David Benson, advised by AOES professor Paul Dirmeyer, has done work to determine thresholds of soil moisture at which the atmosphere becomes overly sensitive to the land surface, and to use the thresholds to identify regions across the United states that are most likely to have heatwaves. These findings have been published in the Journal of Climate (Benson & Dirmeyer, 2020). 

The goal this summer is to determine if subseasonal forecast models do a good job representing these relationships. This may reveal model biases in the aforementioned thresholds of soil moisture, and provide a diagnostic tool for model evaluation which could lead to improvements in heatwave prediction. In addition to diagnosing dynamical models, this framework could also provide a new statistical approach to predict heatwaves exacerbated by soil moisture conditions. Accurate prediction will lead to better measures in planning and allocation of resources to combat heat waves.

 Rachel Gaal’s dissertation work, advised by AOES Professor Jim Kinter, is focused on determining whether soil moisture “memory” can serve as a source of predictability for summer Mesoscale Convective System (MCS) events in the U.S. Great Plains. The MCS is a key player in the water cycle and can be responsible for particularly heavy rain and damaging wind.

Prior research has focused on identifying favorable atmospheric conditions for MCS development; however, summertime MCS in the U.S. Great Plains can occur in unfavorable atmospheric conditions. Other mechanisms, including land-atmosphere interaction and in particular soil moisture state, may be responsible for these initiations. Research on the impact of soil moisture on storm development has focused on ordinary, unorganized thunderstorms rather than MCS events, but some studies suggest that the soil moisture state can influence the location of MCS triggering. By identifying and quantifying the feedbacks between soil moisture and MCS initiation, they expect to improve 1) our understanding of how MCS events form under unfavorable atmospheric conditions and 2) the accuracy of MCS predictions, ultimately mitigating their societal impacts.