Variation in aerosol properties over Hyderabad, India during intense cyclonic conditions

In this study, we examine the changes in aerosol properties associated with an intense tropical cyclone, the so- called ` Mala', that occurred during April 2006, over the Bay of Bengal. This cyclone, accompanied by very strong surface winds reaching 240kmh 21, caused extensive disasters in houses and beach resorts in the coastal areas of Myanmar. Ground- based measurements of aerosol optical depth ( AOD), particle- size distribution and erythemal UV radiation in the neighbouring urban environment of Hyderabad, India, showed significant variations due to changes in wind velocity and direction associated with the cyclone event. The results show an increase in ground- measured PM1.0, PM2.5, and PM10 concentrations, probably associated with the strong surface winds on 28 April, the day on which the cyclone affected the study region. In contrast, the AOD on that day exhibited a significant decrease, since the winds probably acted as a ventilation mechanism for the atmosphere. The Terra- MODIS satellite images showed a prevalence of dust particles over the study region on the next day of the cyclone. Results from ground- based AOD sun- photometer observations matched well with satellite AOD retrievals. Aerosol index obtained from Ozone Monitoring Instrument ( OMI) during the cyclone events suggested increasing trend, indicating the presence of an elevated dust- aerosol layer during and after the cyclone. Results on the effects of wind and air mass fields in affecting the AOD during cyclone events are also presented.