Seasonal and interannual variations of temperature in the tropical tropopause layer (TTL) over Indonesia based on operational rawinsonde data during 1992–1999

Abstract

Seasonal and interannual variations of temperature in the tropical tropopause layer (TTL) during 1992–1999 are investigated on the basis of operational rawinsonde data over Indonesia and surrounding stations at 90–140°E, 15°N–15°S. An annual variation characterized by a warm (cold) anomaly in the northern summer (winter) is observed at all analysis stations. Reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP Reanalysis) and European Centre for Medium‐Range Weather Forecasts (ERA‐40) failed to fully reproduce the observed seasonal variation over Indonesia, especially during northern winter. NCEP Reanalysis data are biased, and ERA‐40 data agreed well only at surrounding stations. These results are reflections of the operational rawinsonde data over Indonesia which are incorrectly reported to the Global Telecommunication Systems (GTS). The cold point tropopause (CPT) temperature varies annually, having a warm (cold) phase in northern summer (winter) and a latitudinal structure having the warmest temperatures over the equator. The latitudinal structure over Indonesia is the inverse of that observed in the zonal and annual mean fields; therefore effective cold trap regions for water vapor dehydration events appear away from the equator. Longitudinally, the CPT temperature is lowest over Indonesia compared to other longitudinal sections and decreases eastward along the equator inside the analysis region (Indonesia). This east‐west gradient in CPT temperature within the analysis region was affected during the 1997/1998 El Niño and 1998/1999 La Niña, but the longitudinal range of effect and time variation of the CPT temperature anomaly was independent of the El Niño and La Niña events.