Convective activities associated with intraseasonal variation over Sumatera, Indonesia, observed with the equatorial atmosphere radar

Abstract

Abstract. The influence of intraseasonal variation (ISV) on convective activities over Sumatera (or Sumatra) is studied by using data derived from the Equatorial Atmosphere Radar (EAR), the Boundary Layer Radar (BLR), the surface weather station, the Geostationary Meteorological Satellite (GMS), and NCEP/NCAR reanalysis. In June 2002, convective activities over the Indian Ocean, the maritime continent, and the western Pacific were significantly modulated by the ISV. Zonal wind observed by EAR and surface pressure observed at the observation site suggested the existence of a Kelvin-wave-like structure of ISV. From temporal variations of T BB , zonal wind at 850 hPa, and vertical shear of horizontal wind between 700 and 150 hPa, we classified the observation periods into the inactive phase (1-9 June), active phase (10-19 June), and postwesterly wind burst phase of ISV (20-26 June). During the inactive phase of ISV, convective activities caused by local circulation were prominent over Sumatera. Results of radar observations indicated the dominance of convective rainfall events over the mountainous area of Sumatera during the inactive phase of ISV. During the active phase of the ISV, cloud clusters (CCs), which developed in the convective envelope of SCC with a period of 1-2 days, mainly induced the formation of convective activities over Sumatera. Results of radar observations indicated that both convective and stratiform rainfall events occurred over the mountainous area of Sumatera during the active phase of ISV. In the postwesterly wind burst phase of ISV, Correspondence to: M. K. Yamamoto (m-yamamo@rish.kyoto-u.ac.jp) convective activities were suppressed over Sumatera. Features of convective activities found over Sumatera generally agreed well with those found in Tropical Ocean and Global Atmosphere/Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). However, local circulation played an important role in the formation of convective activities over Sumatera in the inactive phase of ISV.

Influence of the Madden–Julian Oscillation on Indonesian rainfall variability in austral summer

“…There have been numerous studies on the rainfall variability over Indonesia and its relation to the diurnal change (Mori et al, 2004;Seto et al, 2004;Ichikawa and Yasunari, 2006;Tian et al, 2006;Qian, 2008), the annual change like monsoon (Hamada et al, 2002;Aldrian and Susanto, 2003;Chang et al, 2005) and the interannual large-scale climatic phenomena such as the El Niño-Southern oscillation (Kirono et al, 1999;Haylock and McBride, 2001;McBride et al, 2003;Aldrian and Susanto, 2003;Hendon, 2003;Chang et al, 2004). It is also widely known that the Madden-Julian Oscillation (MJO; e.g.…”

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

“…Murata et al (2006) have shown that an intensification of westerly wind accompanied by SCC can cause a dry-air intrusion from the Indian Ocean to Sumatra in the lower and middle troposphere, and suggested that an appearance of dry air plays a role in suppressing convective activity over Sumatra. Seto et al (2004) also reported that the Sumatra region became convectively inactive after an intensification of lower-tropospheric westerly wind.…”

“…Murata et al (2002) suggested that quasi-10-day variations of convective activity over Sumatra changed in association with synoptic-scale variations of lower-tropospheric zonal wind over the Indian Ocean and Sumatra. Seto et al (2004) have shown a relationship between intraseasonal variability (ISV, see Zhang (2005) and Madden and Julian (1994)) and convection over the mountainous region of Sumatra by a case study during June 2002. They showed that convection caused by topographically-induced local circulation was prominent over the mountainous region of Sumatra during the inactive phase of ISV.…”