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 VHF wind profiler (Equatorial Atmosphere Radar; EAR) installed at West Sumatra (0.2degS, 100.32degE). 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 about 0.09 m/s. 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 almost disappeared.

During 5-6 May, downward motions up to about 0.11 m/s were observed above 14 km, while upward motions were observed below 14 km. Estimation of W by the ECMWF 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 existed over the 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 convectively active region, and leeward downward tilt of isentropes can suppress an upward transport of airmass into the tropical tropopause layer (TTL) by producing downward motions in the TTL.