Interactions Between Asian Air Pollution and Monsoon System—a Multi-Scale Modeling Study

One of the serious side effects of Asia’s rapid economic advancement in recent decades has been the increase in air pollution levels, which threatens the health of more than half of the world population living in the region. Emissions aside, monsoon system has been thought to play a role in changes in air quality in Asia. Monsoon system regulates precipitation and hydrological cycle. The changes in precipitation and airflow associated with monsoon have profound impacts on air quality. On the other hand, high concentrations of aerosols characterizing Asian air pollution can affect monsoon system through complex aerosol-cloud-radiation (ACR) interactions. To better understand the linkage between Asian monsoon and regional air quality, NASA’s Atmospheric Composition: Modeling and Analysis (ACMAP) program funds us to carry out a multi-scale modeling study utilizing the Goddard Earth Observing System Model, Version 5 (GEOS-5) and NASA Unified Weather Research and Forecasting Model (NU-WRF). This presentation will focus on one of three objectives of the proposed study, i.e., how pollution and dust aerosols in Asia affect the monsoon circulation and rainfall via scattering and absorption of solar radiation, changing the atmospheric heating rates, and modifying the cloud properties, based on NU-WRF simulations. NU-WRF is a regional modeling system that represents chemistry, aerosol, cloud, precipitation and land processes at down to near cloud-resolving spatial scales. The Goddard Chemistry Aerosol Radiation and Transport module (GOCART) has been fully coupled with the Goddard microphysics and radiation schemes in NU-WRF that allows investigations of direct and indirect aerosol effects in the climate/weather system. In this study, a series of NU-WRF simulations have been conducted to separate effects from aerosol-radiation (AR) interaction and aerosol-cloud (AC) interaction over the winter and summer monsoon seasons. The relative contributions of AC and AR effects to precipitation and atmospheric circulation will be probed. Their feedback to regional air quality will be investigated. The impact of air pollution on monsoon onset and development will also be discussed.