Atmospheric Moisture Sources, Paths, and the Quantitative Importance to the Eastern Asian Monsoon Region

Abstract

Abstract A Lagrangian model [Flexible Particle dispersion model (FLEXPART)] was used to calculate the back trajectories of air parcels residing over the East Asian monsoon region (EAM) for a 4-yr period (2009–12). To detect the moisture source–sink relationships to the EAM, the moisture budgets [evaporation minus precipitation (E − P)] were evaluated by diagnosing the changes of specific humidity along the trajectories. A circulation constraint method was proposed to define the moisture sources of the EAM, to quantify their importance, to depict the moisture transport processes, and to reveal the fate of the moisture from different sources. The results indicated that in winter the largest airmass inflow is through the dry westerlies, but they do not form net precipitation. The much smaller contribution of the tropical oceans is more relevant to winter precipitation. In summer, the main contribution was through the southwest monsoon, with a mean specific humidity of 9.8 g kg−1 when entering the EAM, providing more than 40% of the moisture to the EAM and making the southwest monsoon the most humid and abundant moisture source of the EAM. Local evaporation plays an important role as a moisture source for the EAM both in summer and winter.