Moisture Transport over the Arabian Sea Associated with Summer Rainfall over Pakistan in 1994 and 2002

摘要

In this study,we aimed to elucidate the critical role of moisture transport affecting monsoon activity in two contrasting summers over the Arabian Sea during the years 1994,a relatively wet year,and 2002,a relatively dry year.A comprehensive diagnostic evaluation and comparisons of the moisture fields were conducted; we focused on the precipitation and evaporation as well as the moisture transport and its divergence or convergence in the atmosphere.Monthly mean reanalysis data were obtained from the National Centers for Environmental Prediction (NCEP-Ⅰ and -Ⅱ).A detailed evaluation of the moisture budgets over Pakistan during these two years was made by calculating the latent energy flux at the surface (E - P) from the divergence of the total moisture transport.Our resnlts confirm the moisture supply over the Arabian Sea to be the major source of rainfall in Pakistan and neighboring regions.In 1994,Pakistan received more rainfall compared to 2002 during the summer monsoon.Moisture flow deepens and strengthens over Arabian Sea during the peak summer monsoon months of July and Augnst.Our analysis shows that vertically integrated moisture transport flux have a significant role in supplying moisture to the convective centers over Pakistan and neighboring regions from the divergent regions of the Arabian Sea and the Bay of Bengal.Moreover,in 1994,a deeper vertically integrated moisture convergence progression occurred over Pakistan compared to that in 2002.Perhaps that deeper convergence resulted in a more intense moisture depression over Pakistan and also caused more rainfall in 1994 during the summer monsoon.Finally,from the water budget analysis,it has been surmised that the water budget was larger in 1994 than in 2002 during the summer monsoon.