Vertical wind observation in the tropical upper troposphere by VHF wind profiler: A case study

Features of upper tropospheric vertical wind (W) over Sumatra, Indonesia, are presented using data observed by a VHF wind profiler installed at West Sumatra (0.2°S, 100.32°E). During 5–9 May 2004, W from the middle to upper troposphere (8–14 km) changed in accordance with the cumulus activity over Sumatra. During 5–6 May, 3-hourly averaged W continuously showed upward motions up to 0.09 m s^−-1. The upward motions were observed in the vicinity of deep convective events, which were continuously seen over Sumatra within a synoptic-scale convectively active envelope. After 7 May, when cumulus activity was suppressed over Sumatra, 3-hourly averaged upward motions of greater than 0.05 m s^−-1 almost disappeared. During 5–6 May, downward motions up to ∼0.11 m s^−-1 were observed above 14 km, while upward motions were observed below 14 km. Estimation of W by the European Centre for Medium-Range Weather Forecasts operational analysis have revealed that a major part of observed downward motions above 14 km is explained by the leeward (southwestward) wind and leeward downward tilt of isentropes that existed over western Sumatra. The observed downward motions above 14 km during 5–6 May suggest that downward motions caused by leeward downward tilt of isentropes can be produced in the vicinity of the convectively active region, and leeward downward tilt of isentropes can suppress an upward transport of air mass into the tropical tropopause layer (TTL) by producing downward motions in the TTL.