Seasonal variation of trend in temperature and ozone over the tropical stratosphere in the Northern Hemisphere

Abstract

Temperature and ozone trends in the stratosphere are investigated using Halogen Occultation Experiment (HALOE) aboard Upper Atmospheric Research Satellite (UARS) observations for the period 1992-2004, over the tropics of Northern Hemisphere (0-30°N). The regression analysis of temperature time series indicates a significant annual cooling trend of 1-3 K/decade in the free stratosphere. A cooling trend of ~2±0.6 K/decade near 25 km which increases with altitude to reach a maximum around 35 km and then decreases to 1±1.1 K/decade near stratopause is computed. The observed maximum cooling trend near 35 km may be viewed with caution due to the change over of temperature from National Centre for Environmental Prediction (NCEP) reanalysis data to HALOE instrument. A statistically significant decreasing ozone trend in the lower stratosphere is also obtained which becomes negligible above 40 km. Attempt has been made to compute the seasonal trend components in both temperature and ozone. Seasonal distribution of temperature trends shows a maximum cooling during winter. The largest negative ozone trend is found during autumn with a peak (8-10% per decade) near 30 km.