Effect of the onset of southwest monsoon on the atmospheric electric conductivity over the Arabian Sea

Abstract

Measurements of the atmospheric electric conductivity and small, intermediate, and large ion concentrations made at four locations over the Arabian Sea onboard ORV Sagarkanya in the premonsoon and monsoon seasons during the Arabian Sea Monsoon Experiment in 2002-2003 are reported. Observations show a threefold increase in the daily average value of conductivity over a period of ~10 days preceding the onset of southwest monsoon. The enhanced values of conductivity are accompanied with a higher concentration of large ions. Although ion concentrations in all categories exhibit large fluctuations, the average concentration levels of small ions decrease and of large ions increase during the monsoon period. It is proposed that the enhancement in conductivity associated with the onset of monsoon is due to the highly charged large ions produced by the bubble bursting process at the air-sea interface caused by the breaking waves during the high-wind-speed periods over the Arabian Sea. The correlation coefficient between the large ion concentration and wind speed measured at Sagarkanya is found to increase from 0.41, 0.16, and 0.23 in the premonsoon and two monsoon periods to 0.56 during the monsoon onset period. The enhanced value and the large variability of large ion concentrations observed during the monsoon season are associated with the spatial and temporal heterogeneity in not only their production but also their dissipation by the cloud scavenging processes over the Arabian Sea.