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Howard University (2010)

The Impacts of Chihuahua Desert Aerosol Intrusions on Convective Clouds and Regional Precipitation

Apodaca, Karina

Titre : The Impacts of Chihuahua Desert Aerosol Intrusions on Convective Clouds and Regional Precipitation

Auteur : Apodaca, Karina

Université de soutenance : Howard University

Grade : Doctor of Philosophy (PhD) 2010

Résumé
Growing up in a desert region influenced by a monsoon system and experiencing, first-hand, dust storms produced by convective thunderstorms stimulated my interest in the study of the impacts of aerosols on clouds. Contrary to other studies which focus more on anthropogenic aerosols, I chose to investigate the role of natural aerosols in the deserts of North America. Moreover, the role played by aerosols in desert regions within the North American Monsoon domain has not received as much attention as in other monsoon regions around the world. This dissertation describes my investigation of the connection between mineral aerosols (dust storms) and monsoon rainfall in the deserts of the Southwestern United States and Northwestern Mexico. To develop the context for the study of the role of mineral dust in summer-time convection on a regional scale, large-scale dynamical processes and their impact on the inter-annual variability of monsoon rainfall were analyzed. I developed the climatology of monsoonal rainfall and dust storms using surface observations to determine which mesoscale features influence North American Monsoon rainfall in the Paso Del Norte region. The strongest correlations were found between sea surface temperatures over the Gulf of California, Gulf of California moisture surges and monsoon rainfall in the Paso Del Norte region. A connection to ENSO could not be clearly established despite analyzing twenty-one years of data. However, by breaking the data into segments, a strong correlation was found for periods of intense rainfall. Twenty-one case studies were identified in which dust storms were produced in conjunction with thunderstorms during the 2005 - 2007 monsoon seasons. However, in some cases all the conditions were there for rainfall to occur but it did not precipitate. I concluded that strong thunderstorm outflow was triggering dust storms. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem V3.1.1) was used to evaluate the model’s sensitivity to the inclusion of aerosol effects on cloud drop formation and on direct radiative forcing. A comparison of the relative contribution of aerosol direct and indirect forcings in terms of differences in aerosol and cloud optical thicknesses, cloud water content, cloud droplet number, and short wave and long wave radiation, revealed that cloud cover is reduced. This suggests that Chihuahua desert dust affects cloud formation.

Présentation

Page publiée le 11 novembre 2013, mise à jour le 11 décembre 2019