Colored Moisture Analysis Estimates of Variations in 1998 Asian Monsoon Water Sources

Abstract

This study investigated the dynamic motion of atmospheric water advection by an analytic method called colored moisture analysis (CMA), that allows for the estimation and visualization of atmospheric moisture advection from specific source regions. The CMA water transport model includes balance equations with the upstream scheme and, uses external meteorological forcings. The forcings were ob- tained from the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiments (GAME) reanalysis. A numerical simulation with 79 global sections was run for April to October 1998. The results clearly showed seasonal variations in advection associated with large-scale circulation fields, particularly a difference between rainy and dry seasons associated with the Asian monsoon. The paper also proposes a new definition of southwest Asian monsoon onset and decay, based on the amount of water originating from the Indian Ocean. Earliest onset occurs over southeastern Indochina around 16- 25 May. Subsequent onset occurs in India one month later. These results agree with previous studies on the Asian monsoon onset/end. The CMA provides a clearer, more integrated view of temporal and spatial changes in atmospheric circulation fields, particularly Asian monsoon activities, than previous studies that focused only on one or two distinct circulation features, such as precipitation or wind speed. Fur- thermore, monsoon transition in a specific year, 1998, first became analyzable, whereas the previous studies used climatologies.