Variations of the Tropopause Over Different Latitude Bands Observed Using COSMIC Radio Occultation Bending Angles

Abstract

The tropopause is a transition layer between the troposphere and the stratosphere. The exchange of air, water vapor, trace gases, and energy between the troposphere and the stratosphere occurs in this layer. Accurate and continuous observations of the tropopause on a global scale are crucial for monitoring stratosphere-troposphere exchange and understanding the properties of atmosphere in the upper troposphere and lower stratosphere. In this paper, the tropopause heights are identified from Global Positioning System radio occultation (RO) bending angle profiles using the covariance transform method. Temporal variations of the tropopause parameters, including the tropopause height, temperature, and pressure at different latitude bands are investigated using the RO observations from the Constellation Observing System for Meteorology, Ionosphere and Climate mission during the period from January 2007 to December 2011. We divide the Earth into 18 nonoverlapping latitude bands 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> wide. Monthly averages of the tropopause parameters weighted by area are calculated at each latitude band and the temporal variations of these tropopause parameters are analyzed. The results indicate that the latitudinal variation patterns of the tropopause parameters in the Northern Hemisphere are different than those in the Southern Hemisphere. The relationship between the variations of different tropopause parameters is studied. The results show that the variation of the tropopause temperature and pressure is negatively correlated with that of the tropopause height in most of the latitude bands. In addition, the trend of the variation of the tropopause height in each latitude band is calculated with the median of pairwise slopes regression method. We find that the overall trend in the tropopause height varies in different latitude bands. The global average tropopause height decreases ~ 7 m/a during the period from 2007 to 2011.