Contributions of Asian Pollution and SST Forcings on Precipitation Change in the North Pacific

Previous research indicates that the aerosol effect from Asian pollution outflow could account for the trend of increasing deep convective clouds, as well as an intensification of the storm track, over the North Pacific Ocean in winter since the mid-1990s. However, it is not clear whether such change is solely due to Asian pollutant forcings or not. To understand the relative roles of Asian pollutant aerosols and sea surface temperature (SST) forcings on the precipitation change in the North Pacific, we examine the interannual variation of particulate matter 2.5 (PM2.5) simulated in the global chemical transport model (GEOS-Chem) and the idealized experiments using the Community Atmosphere Model version 5 (CAM5) for 1986-2010. The composite analysis indicates that the changes in precipitation amount and storm track intensity in the southwestern North Pacific might be associated with the increase in PM2.5 concentration in East China. However, El Niño-like warming during the years of high PM2.5 concentration may also influence the precipitation amount, as well as the storm track intensity in the central and eastern North Pacific. Model experiments also indicate that the El Niño-like warming and the Asian pollutant aerosols have different effects on precipitation amounts in the North Pacific. Therefore, the precipitation changes, as well as the intensification of the storm track, in the North Pacific might be attributed to both Asian pollutant aerosols and SST forcing in the tropics.