JAMEX2009: Field experiment to develop a physical basis for CCN parameterization over central Nepal

The initial droplet spectra arising from CCN parameterization can have a profound impact in the evolution of clouds (Khain et al. 2000, Tao et al.2004). In fact, aerosol particle size, its chemical composition and water solubility are critical for the particles' ability to serve as cloud condensation nuclei and hence determining the CCN number concentration at different saturations. The Joint Aerosol –Monsoon Experiment (JAMEX) was conducted in Nepal during 2009 pre-monsoon season coinciding with the build-up period of aerosol in the region. The campaign's objective was to collect data necessary to address the aerosol-monsoon water cycle dynamics: the EHP effect (Lau et al 2006, Lau and Kim 2006), the solar dimming effect (Ramananthan et al 2005), transport of dusts, and microphysical effects (especially the effect of CCN). In order to acquire data for modeling the effect of CCN on aerosol-cloud rainfall interaction, field measurements were carried using filters and aerosol spectra were concurrently measured using SMPS. Here, an overview of the field experiment and field data are presented.