A study of tropical tropopause using MST radar

K. Satheesan,B. V. Krishna Murthy

doi:10.5194/angeo-23-2441-2005

Abstract

Abstract. Using the MST radar data of vertical wind, the characteristics of the tropical tropopause, following four different definitions, depending on 1) temperature lapse rate, 2) cold point, 3) convective outflow and 4) potential temperature lapse rate minimum, are studied. From the vertical wind data of the radar, the altitude profiles of temperature and horizontal divergence are derived, from which the tropopause levels corresponding to i) the lapse rate ii) cold point iii) convective outflow level and iv) potential temperature lapse rate minimum are determined. The convective outflow level and hence the convective tropopause altitude is determined, for the first time using the MST radar data. The tropopause altitudes and temperatures obtained following the four definitions are compared on a day-to-day basis for the summer and winter seasons. Winter and summer differences in the tropopause altitude and temperature are also studied. Keywords. Meteorology and atmospheric dynamics (convective process; middle atmosphere dynamics; tropical meteorology)

Highlights

The tropical tropopause has become the focus of scientific interest spurred largely by a realization that the tropics hold the key to the variability in global climate
Simple models suggested that the cold point in the temperature profile is a stratospheric feature which does not depend upon convection, owing its existence mainly to the photochemical production of ozone near the 100 hPa level (Kirk-Davidoff et al, 1999; Thuburn and Craig, 2002)
The results presented above are in general agreement, especially for the cold point and convective tropopauses

Summary

Introduction

The tropical tropopause has become the focus of scientific interest spurred largely by a realization that the tropics hold the key to the variability in global climate. It appears that the tropospheric upward flow leading to horizontal divergence in winter, driven mainly by the extra tropical waves, penetrates into the lower stratosphere, whereas the relatively stronger horizontal divergence in summer, driven mainly by the local convection, is confined to tropospheric altitudes. These studies should be extended with a larger database and at more locations using radar which gives more reliable and direct information on convection than the indirect methods using the satellite-based cloud cover and Outgoing Long wave Radiation (OLR) data. It would be of interest to compare the divergence/convergence profiles obtained by MST radar with those from a colocated cm wavelength radar during strong convective storm events

Determination of lapse rate minimum tropopause

Conclusions