Short-Term Variations of the Tropopause Height over the Winter MONEX Area

Abstract

An observational study of short-term (?1 week) tropical tropopause height variations has been undertaken using measurements from the December 1978 Winter Monsoon Experiment (Winter MONEX). Sounding data from three Soviet ships in the southern South China Sea and conventional rawinsonde stations in the region of the Indonesian maritime continent am used in the analysis. During a one-week period (10-17 December), a ?1.5 km reduction in the height of the tropopause and a warning of 5-8°C in the lower stratosphere were observed over the southern South China Sea. Outside this region a systematic lowering of the tropopause was not observed. In the region of tropopause descent there was a concurrent increase in the amount of deep convective activity. Within the time period of them events, two winter monsoon cold surges (on the l0th and 15th) and a weak tropical depression (on the 14th) affected the circulation over the South China Sea. During the period of tropopause lowering. tropospheric pressure height and surface pressure falls (having amplitudes ?20 m and 4 mb, respectively) were observed over the northern South China Sea. These observations suggest that the tropopause descent and lower-stratospheric warming may be a consequence of regional dynamical processes which are analogous to those occurring during the development of cyclones at midlatitudes. While dynamical processes seem to be a likely explanation for the observed variations, other process related to the increased convective activity in the region may also play a role. Several such mechanisms are discussed.