An analysis of downwelling IR fluxes over the Indian Ocean using cloud radar reflectivity for pre-monsoon and monsoon periods during JASMINE

During leg II (May 4 - June 5) of the 1999 Joint Air-sea Monsoon Inteaction Experiment (JASMINE) in the Bay of Bengal, simultaneous measurements were made by two Eppley standard precision infrared (PIR) hemispherical flux radiometers and the NOAA cloud radar. We discuss the technique used to determine cloud base, thickness, type and frequency using radar reflectivity, and its application to analyzing cloud forcing on downwelling IR fluxes. Two case studies are presented: pre-monsoon and monsoon, both 6-day periods occurring within the month-long ship cruise experiment.

Radiative cloud forcing over the Indian Ocean is an integral component of the coupled ocean-atmoshpere phenomena affecting intraseasonal variability of the Asian-Australasian monsoon system. Previous diagnostic studies in the Pacific suggest that variability in the Asian-Australasian region has climatic consequences on a global scale that influences interannual variability in the west. It is the scope of JASMINE to investigate the intraseasonal variability of the Asian monsoon as a result of the ocean-atmosphere interaction, and provide data for model evaluation, parameterization, and diagnostic study. In this analysis, we investigate the role of radiative cloud forcing during one specific monsoon process.