THE JOINT AEROSOL– MONSOON EXPERIMENT A New Challenge for Monsoon Climate Research

Understanding the physical processes responsible for aerosol– monsoon water cycle interactions is fundamental to improving prediction and enhancing vigilance of climatic hazards in the Asian monsoon region. A ir pollution and monsoon floods and droughts are two of the most serious environmental threats to over 60% of the world population living in Asia. The increasing aerosol loading in Asian countries associated with industrialization during the last two decades has caused major health-related problems associated with worsening air quality and has also impacted aviation safety. Recent field experiments over the South Asian (Ramanathan et al. 2001) and East Asian (Conant et al. 2003; Li et al. 2007a) regions have found that anthropogenic aerosols may significantly change the energy balance of the atmosphere and at the Earth's surface. General circulation model (GCM) studies have suggested that anthropogenic aerosol forcing could influence the seasonal rainfall distribution in the monsoon regions over South (Ramanathan et al. 2001, 2005; Chung et al. 2005) and East Asia (Menon et al. 2002). Others have demonstrated the importance of the atmospheric heating by elevated absorbing aerosols (dust and black carbon) in | spurring anomalous water cycle feedback, affecting the general circulation and altering the radiation and dynamical states of the entire monsoon system (Lau et al. 2006; Lau and Kim 2006). To address the scientific issues of elevated aerosols and their interaction with the large-scale monsoon circulation, the international workshop " Effects of Elevated Aerosols on the Radiation and Dynamics of the Monsoon Water Cycle " was held duringticipants exchanged the latest scientific findings on aerosol and monsoon research and provided updates on a number of related national research programs in China, India, Japan, Italy, and the United States and their connections with international programs. This article describes the scientific rationale and the challenges of studying aerosol–monsoon water cycle interaction and outlines a proposal for joint aerosol–monsoon research, based on recommendations by the workshop participants, as well as follow-up discussions with interested scientists. BACKGROUND. Long recognized as a major regional environmental hazard in causing severe health problems and problems in aviation safety, aerosols are now known to have strong impacts on both regional and global climates. It has been estimated that aerosol may reduce by up to 10% of the