Observing and understanding the Southeast Asian aerosol system by remote sensing: An initial review and analysis for the Seven Southeast Asian Studies (7SEAS) program

Southeast Asia (SEA) hosts one of the most complex aerosol systems in the world, with convoluted meteorological scales, sharp geographic and socioeconomic features, high biological productivity, mixtures of a wide range of atmospheric pollutants, and likely a significant susceptibility to global climate change. This physical complexity of SEA is coupled with one of the worldʹs most challenging environments for both in situ and remote sensing observation. The 7-Southeast Asian Studies (7SEAS) program was formed to facilitate interdisciplinary research into the integrated SEA aerosol environment via grass roots style collaboration. In support of the early 7SEAS program and the affiliated Southeast Asia Composition, Cloud, Climate Coupling Regional Study (SEAC4RS), this review was created to outline the network of connections linking aerosol particles in SEA with meteorology, climate and the total earth system. In this review, we focus on and repeatedly link back to our primary data source: satellite aerosol remote sensing and associated observability issues. We begin with a brief rationale for the program, outlining key aerosol impacts and, comparing their magnitudes to the relative uncertainty of observations. We then discuss aspects of SEAʹs physical, socio-economic and biological geography relevant to meteorology and observability issues associated with clouds and precipitation. We show that not only does SEA pose significant observability challenges for aerosol particles, but for clouds and precipitation as well. With the fundamentals of the environment outlined, we explore SEAʹs most studied aerosol issue: biomass burning. We summarize research on bulk aerosol properties for SEA, including a short synopsis of recent AERONET observations. We describe long range transport patterns. Finally, considerable attention is paid to satellite aerosol observability issues, with a face value comparison of common aerosol products in the region including passive and active aerosol products as well as fluxes. We show that satellite data products diverge greatly due to a host of known artifacts. These artifacts have important implications for how research is conducted, and care must be taken when using satellite products to study aerosol problems. The paper ends with a discussion of how the community can approach this complex and important environment.