Date of Award

1-1-2017

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Atmospheric and Environmental Sciences

Content Description

1 online resource (xvii, 99 pages) : color illustrations, color maps.

Dissertation/Thesis Chair

Wei-Chyung Wang

Committee Members

Aiguo Dai, Robert Fovell, Jen-Ping Chen

Keywords

Aerosol spatial distribution, Aerosol-cloud interactions, Meiyu front, Yangtze-Huai River Valley, Fronts (Meteorology), Atmospheric diffusion, Aerosols, Air

Subject Categories

Atmospheric Sciences

Abstract

The observed contrasts in both aerosol number and size associated with frequent north-polluted-south-clean (NPSC) conditions over Yangtze-Huai River Valley (YHRV) during the Meiyu season may induce different aerosol-cloud-radiation interactions within the region causing different evolution of the Meiyu system. This aspect was studied by conducting WRF sensitivity simulations with different configurations of north-south aerosol number and size contrasts. Results show that when the Meiyu system develops at YHRV, more aerosols in the north (than the south) cause more but smaller cloud droplets to form, resulting in stronger radiative cooling at north part of the Meiyu system. Subsequently, the differential cooling induces a thermal direct circulation, yielding stronger subsidence behind the front and low-level northerly winds across the front. Affected by Coriolis force and surface friction, the enhanced northerly winds increase horizontal wind shear and vorticity along the front, which favors the development of mesoscale disturbance. Meanwhile, fewer aerosols in the south producing fewer and larger cloud droplets weaken both radiative and evaporative cooling at south part of the Meiyu system. It leads to a weaker cold pool, and thus limits the southward extending of frontal precipitation. Ensemble simulations with different initial conditions further suggest that this phenomenon becomes more significant when the north-south gradient of aerosol number concentration increases or the baroclinicity of Meiyu fronts is weaker.

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