Extremes in total ozone content over northern India

Abstract

Using daily station total ozone data from TOMS on Nimbus‐7 (1979–1993) and Earth Probe (1997–2005) satellites of National Aeronautics and Space Administration (NASA)/Goddard Space Flight Center (GSFC) during the period 1979–2005, the characteristic features of extremes in the total ozone content and the frequency of the low/high ozone days have been carried out over the northern parts of India in the winter season. Stations located in the north of 20° N latitude regions of India have been chosen for the study. To determine whether the day is a low, high or normal ozone day, the statistical percentile thresholds are computed based on the daily data during winter months (January and February). It has been observed that the trends in the frequency of low ozone days are increasing and for the high ozone days are decreasing during 1979–1993. Similarly the trends in the highest total ozone reaching during January and February are decreasing. The recent period (1997–2005) shows opposite trends that are not statistically significant or stable during the period. Even the mean total ozone during January and February for the period 1979–1993 show the decreasing trends. Overall the trends in the total ozone extremes and the frequency of low/high ozone days are found to be decreasing over the northern parts of India during the winter season.

Acknowledgements

The authors wish to thank Prof. B. N. Goswami, Director, IITM for all the necessary facilities provided to carry out the present study and also to Dr. Nityanand Singh, Head of Climatology and Hydrometeorology Division, for constant encouragement.