Evolution of a Super Cloud Cluster and the Associated Wind Fields Observed over the Indonesian Maritime Continent during the First CPEA Campaign

Abstract

A special tropospheric observation was conducted during 10 April-09 May 2004 as a part of the first campaign of the Coupling Processes in the Equatorial Atmosphere (CPEA-I), using upper soundings at seven stations in/around Sumatera, and weather radar and wind profilers at Kototabang (KT; 100.32 E, 0.20 S, 865 m above mean sea level), West Sumatera. A super cloud cluster (SCC) with a westerly wind burst (WWB) propagated eastward over the Indonesian Maritime Continent during 04-07 May. In the present report, we examine the evolution of that SCC and the associated wind behavior in detail, usingCorresponding author: Yoshiaki Shibagaki, Faculty of Information and Communication Engineering, Osaka Electro-Communication University, 18-8 Hatsu-cho, Neyagawa, Osaka 572-8530, Japan. E-mail: sibagaki@maelab.osakac.ac.jp ( 2006, Meteorological Society of Japan Geostationary Operational Environmental Satellite (GOES-9) Infrared (IR) data and CPEA observations. During the analysis period, the SCC developed over the eastern Indian Ocean, decayed rapidly as it reached Sumatera, and re-developed over Kalimantan. The eastward propagation of SCC resulted from the successive formation of meso-scale cloud clusters (CCs) with westward propagation. The transition of the SCC was related to the evolution of CCs. A CC generated over Sumatera began to diminish as the WWB arrives at a mountain range in western Sumatera, but it dominated in/around the mountain range for @9 hours. From upper sounding data aligned along the equator, it was found that the migration speed of the WWB over Sumatera was approximately half that over the sea region between Sumatera and Kalimantan, due to the orography of the Indonesian Maritime Continent. In western Sumatera, the peak height of the WWB at the mountain range ascended 1.5 km from that on the windward side. This shows that the eastward migration of the WWB was intercepted by the mountain range. The orographic influence on the WWB is considered to persist during the retention of the CC in its vicinity. Further, we reveal features of the orographic precipitation associated with the WWB and the detailed wind structure inside the SCC over the mountain range, from radar observations at KT.

Comparison Study of Lower-tropospheric Horizontal Wind over Sumatra, Indonesia Using NCEP/NCAR Reanalysis, Operational Radiosonde, and the Equatorial Atmosphere Radar

“…Smaller correlation coefficient in meridional wind suggests that contributions of local-scale phenomena were greater for meridional wind. Previous studies showed that radar zonal wind shows consistent change with synoptic-scale disturbances such as ISV (Seto et al 2004;Shibagaki et al Fig. 1.…”

Observational Study on Westerly Wind Burst over Sumatra, Indonesia by the Equatorial Atmosphere Radar A Case Study During the First CPEA Campaign

“…A convectively active region in the SCC, as observed by T BB smaller than 240 K, started to move eastward from the Indian Ocean around 3 May, then reached Sumatra around 5 May. The SCC reached the west coast of Borneo (around 110 E) on 7 May (Shibagaki et al 2006b). Although SCCs originating over the Indian Ocean tend to decay around Sumatra (Dunkerton and Crum 1995;Nitta et al 1992), this SCC moved eastward without significant decay around Sumatra, and reached around 150 E from 10 to 12 May.…”

“…2a is the last SCC which passed over Sumatra during the convectively active phase of the ISV at Sumatra (from 23 April to 6 May). Shibagaki et al (2006b) have shown convective features in Sumatra associated with the ISV event during the CPEA-I observation campaign (from 10 April to 9 May 2004).…”

“…They further showed that cloud clusters (CCs), which have a period of 1-2 days and horizontal scale of several hundred kilometers, developed around Sumatra within a convective envelope of synoptic-scale super cloud clusters (SCCs) and mainly caused rainfall events over Sumatra during the active phase of the ISV (See Nakazawa (1988) for the definition of CC and SCC). Shibagaki et al (2006a) used data derived from weather satellite, weather radar, radiosondes, and wind profilers to show a multi-scale structure of convective systems over Sumatra, which range from synoptic (SCC) scale to meso-g scale.…”

“…While several studies focus on the convective period (e.g., Kawashima et al 2006;Shibagaki et al 2006b;Renggono et al 2006), we focus on the period in which convective activity over Sumatra was suppressed. An eastward-moving convective envelope of SCC developed over the Indian Ocean reached to Sumatra on 5 May, and then reached to the east of Sumatra on 7 May.…”