Tropopause characteristics over a southern subtropical site, Reunion Island (21°S, 55°E): Using radiosonde‐ozonesonde data

Abstract

In this paper, we present tropopause characteristics using in situ radiosonde‐ozonesonde observations carried out over the past 13 years (September 1992 to February 2005) from a southern subtropical site, Reunion Island (21°S, 55°E). Three kinds of tropopause definitions, namely, cold‐point tropopause (CPT), lapse rate tropopause (LRT), and ozone tropopause (OT), are characterized. The ozone tropopause for Reunion is appropriately defined as the height at which the vertical gradient of the ozone mixing ratio exceeds 55 ppbv/km and the ozone mixing ratio is over 75 ppbv. The overall height distribution of the three kinds of tropopause ranges in between 12.5 and 18.5 km. Of the three definitions, CPT follows higher heights of distribution, followed by LRT and then OT. The sharpness of tropopause height detection for LRT and OT has been examined, and it has been found that the detection frequency of a definite OT is larger than that for LRT. The results also showed no indefinite OT for a subtropical station in comparison to the results obtained for Northern Hemisphere midlatitude and high‐latitude stations. After adopting a few modifications in the sharpness of ozone tropopause detection, the result remains the same, with a single indefinite case. The indefinite ozone tropopause case was identified when Reunion Island was located nearer to the divergence zone of wind as well as in the anticyclonic region of jet stream entrance. The LRT sharpness results are found to be in good agreement with the other published definition.