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The Chinese University of Hong Kong (2009)

Trends in tropical rainfall during 1979-2008 and their relation with aerosols

Har, Tsoen Hei

Titre : Trends in tropical rainfall during 1979-2008 and their relation with aerosols

Auteur : Har, Tsoen Hei

Université de soutenance : The Chinese University of Hong Kong

Grade : Master of Philosophy in Geolnformation Science 2009

Présentation
Trends of the probability distribution fiinction (PDF) of the Global Precipitation Climatology Project (GPCP) pentad rainfall over the tropics are analyzed separately over land and ocean for the period 1979-2007. Linear trend analyses show that over the ocean, there are significant increases in the heavy rain and light rain (drizzle) categories while a decrease is observed in moderate rain, consistent with the trends found in the global tropics. However, over land, light rain shows a significant decrease, which is opposite to that over the ocean. Rainfall occurs more frequently over tropical sea, while increasing occurrence of drought and heavy rain are found over tropical land.
The rain rate PDFs are further analyzed based on the amount of aerosol as indicated by the Aerosol Optical Depth (AOD) retrieved from the Moderate Resolution Imaging SpectroRadiometer (MODIS). The 29-year averages of light rain and heavy rain decrease with AOD interval. Light rain and heavy rain both give positive trends for all AOD categories but with decreasing magnitude. For regions with AOD > 0.5,heavy rain has the largest linear trend. Highly polluted areas experience less occurrence of rainfall, as evidenced by the increasing rainless occurrence in high AOD areas. The results suggest the suppression of light rain by aerosols in highly polluted areas and the invigoration of intense rain by aerosols.
Specific case studies are carried out in the southeast China, northern India and the Sahara desert. For both southeast China and northern India, heavy rain occurs morefrequently over the past 29 years. The total rainfall over the Saharan area shows a significant decrease over the past 29 years. Rainfall occurs less frequently for all rain rate bin values over the past 29 years with the fractional decrease up to 85%. The huge negative trends in the first few rain rate bins are responsible for the decrease in light rain over the whole land area

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Page publiée le 21 avril 2017, mise à jour le 13 juin 2018