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Aerosol Impacts on Deep Convective Storms in the Tropics: a Combination of Modeling and Observations

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July 18, 2012
Rachel Storer
Hosted by Sue van den Heever (advisor), Graeme Stephens, Dick Johnson, Richard Eykholt (Physics)

Abstract

It is widely accepted that increasing the number of aerosols available to act as cloud condensation nuclei (CCN) will have significant effects on cloud properties, both microphysical and dynamical. This work focuses on the impacts of aerosols on deep convective clouds (DCCs) in the tropical East Atlantic, where dust from the coast of Africa frequently is available to interact with convective storms over the ocean. Two studies were completed, one modeling and one observational, both of which showed evidence that increased aerosols invigorate deep convection.

The first study investigates the effects of aerosols on tropical DCCs with a series of large-scale cloud-resolving model simulations. Polluted simulations contained more deep convective clouds, wider storms, higher cloud tops and more convective precipitation across the entire domain. A detailed microphysical budget analysis was performed to determine the important processes involved in producing precipitation and in affecting the buoyancy of storm updrafts.

The goal of the second study was to examine observational data for evidence that would support the findings of the modeling work. In order to do this, four years of CloudSat data were analyzed over a region of the East Atlantic, and the satellite data were combined with information about aerosols taken from the output of a global transport model. Overall, the cloud center of gravity, cloud top, rain top, and ice water path were all found to increase with increased aerosol loading. These findings are in agreement with what was found in the modeling work, and are suggestive of convective invigoration with increased aerosols. The aerosol effects were found to be largely independent of the environment. A simple statistical test suggests that the difference between the cleanest and most polluted clouds sampled are significant, lending credence to the hypothesis of convective invigoration. This is the first time evidence of deep convective invigoration has been demonstrated within a large region and over a long time period, and it is quite promising that there are many similarities between the modeling and observational results.

It is widely accepted that increasing the number of aerosols available to act as cloud condensation nuclei (CCN) will have significant effects on cloud properties, both microphysical and dynamical. This work focuses on the impacts of aerosols on deep convective clouds (DCCs) in the tropical East Atlantic, where dust from the coast of Africa frequently is available to interact with convective storms over the ocean. Two studies were completed, one modeling and one observational, both of which showed evidence that increased aerosols invigorate deep convection.

The first study investigates the effects of aerosols on tropical DCCs with a series of large-scale cloud-resolving model simulations. Polluted simulations contained more deep convective clouds, wider storms, higher cloud tops and more convective precipitation across the entire domain. A detailed microphysical budget analysis was performed to determine the important processes involved in producing precipitation and in affecting the buoyancy of storm updrafts.