Aerosol indirect effects as a function of cloud top pressure

Abstract

Aerosol indirect effects are quantified as a function of cloud top pressure over India and the Indian Ocean in February and March 2003-2005 from analyses of moderate resolution imaging spectroradiometer ( MODIS) radiances, reflectance, and aerosol optical depth data. We test the hypothesis that aerosol indirect effects are present throughout the troposphere. Theoretical cloud reflectance values are calculated by application of the discrete-ordinate DISORT multiple scattering program, as a function of cloud top pressure, aerosol optical depth, and cloud phase ( i.e., liquid droplets and cloud ice), and are compared to MODIS cloud reflectance data at 1.38 and 3.75 mu m. Aerosol indirect effects are apparent for pressure levels associated with liquid droplets; that is, derivatives of cloud reflectance with respect to aerosol optical depth at 3.75 mu m for liquid droplets over land and ocean are larger than corresponding derivatives associated with theoretical aerosol direct effects. Aerosol indirect effects are not apparent for pressure levels associated with tropospheric ice crystals.