Temporal Distribution of Total Column Ozone over Cochin—A Study Based on <i>in Situ</i> Measurements and ECMWF Reanalysis

Abstract

The variability of Atmospheric ozone is very important to understand the radiative balance of the earth-atmospheric system and climate change. In order to understand the temporal variability of total column ozone (TCO) over the coastal station Cochin (9.95 ° N, 76.27 ° E), we used the ECMWF (European Centre for Medium-Range Weather Forecasts) reanalysis TCO and ground based measurements using Microtop II Sun Photometer (Ozonometer). The trend, seasonal changes and diurnal variation of ozone concentration have been studied in detail for the period 1981-2014. Cochin is a tropical coastal station with tropical monsoon climate and hence we examined the variability of TCO during pre-monsoon (March-May), monsoon (June-September) and post monsoon (October-December) seasons. Significant variations are noted in the TCO for the different seasons during the period of study. Based on the measurements and analysis, it is observed that TCO is maximum during monsoon and minimum during pre- and post-monsoon. We computed the TCO climatology for pre-monsoon (262.0 DU), monsoon (275 DU) and post-monsoon (253 DU) seasons and found that TCO shows a decadal trend (solar cycle). During monsoon season TCO varies with an increase of approximately 14 DU from the pre-monsoon value and a decrease of 22 DU from the post-monsoon value. The increase in TCO concentration during monsoon may be attributed to the monsoonal wind circulations and organized convection. The validation of ECMWF TCO with in situ measurements using Microtop II Ozonometer has been carried out for the year 2015 and found that the values are positively correlated. The diurnal variability of TCO was examined for vernal and autumnal equinox days and noticed the change in variability.