Case Study of an Intense Wind Event Associated with a Mesoscale Convective System in West Sumatera during the HARIMAU2006 Campaign

Abstract

In this study, the processes responsible for an intense wind event that occurred in west Sumatera on November 19, 2006, during the first campaign of the Hydrometeorological ARay for Isv-Monsoon AUtomonitoring (HAR-IMAU) were investigated.Strong winds of 17 m s À1 and a sudden temperature drop of 5 K were observed at an X-band Doppler radar site associated with the passage of a convective system, and some houses were severely damaged. The convective system developed under an environment of strong low-level easterly vertical shear associated with the easterly region of an equatorial Rossby wave. The northern part of the convective system possessed qualitatively similar structures to midlatitude bow echoes, including the convex shape of the convective line, a descending rear-inflow jet positioned at its apex, and mesoscale vortices on both sides of the rear-inflow jet. The low-level wind behind the convective system formed a channel of strong easterly wind as it passed through an area of relatively low topography in the mountain range. The enhanced easterly wind was thought to contribute to the formation of the bow echo-like structure in the northern part of the convective system. This easterly rear-inflow jet was further accelerated in the convective system and descended near the leading edge, forming divergent strong winds at the surface.The sounding data that were taken after the passage of the convective system indicated that dry air appeared in the lower troposphere associated with an enhancement of the southerly component of the wind. An analysis of objective reanalysis data suggests that the southerly was probably associated with westward-propagating mixed Rossby-gravity waves with a period of approximately 5 days. It is suggested that the dry air intruded into the convective system across the back edge of the precipitation area and caused enhanced evaporative cooling, which resulted in the e¤ective downward transport of the enhanced easterly momentum.

Maritime continent coastlines controlling Earth’s climate

“…These diurnal variations have been confirmed everywhere along the coastal zones of larger islands (Sumatera, Kalimantan, Jawa, Sulawesi, and Papua) of the IMC, based on wind profilers (including raindrop measurements) (e.g., Renggono et al 2001;Hadi et al 2002;Murata et al 2002;Araki et al 2006;Marzuki et al 2009;Tabata et al 2011b), precipitation radars (e.g., Kawashima et al 2006Kawashima et al , 2011Wu et al 2007Wu et al , 2013Sakurai et al 2009Sakurai et al , 2011Mori et al 2011;Kamimera et al 2012), a space-borne precipitation radar (e.g., Sorooshian et al 2002;Mori et al 2004;Kikuchi and Wang 2008;Peatman et al 2014), GPS radio occultation (precipitable water or moisture) sounding (e.g., Wu et al 2003, and satellite observations of outgoing longwave (infrared) radiation (OLR) (cloud-top temperature or height) (e.g., Hendon and Woodberry 1993;Nitta and Sekine 1994;Ohsawa et al 2001;Yang and Slingo 2001;Sakurai et al 2005;Hamada et al 2008). As categorized by Kikuchi and Wang Sui et al 1997).…”

“…Our proposal for the Hydrometeorological ARray for Intraseasonal variation −Monsoon AUtomonitoring (HARIMAU) 8 was approved as a JEPP project and was conducted from August 2005 to March 2010 (see: http://www.jamstec.go.jp/iorgc/harimau/HARIMAU.html), in collaboration with the Japan Agency for Marine−Earth Science and Technology (JAMSTEC), Kyoto University, Hokkaido University, the Agency for the Assessment and Application of Technology (BPPT), the Indonesian National Institute of Aeronautics and Space (LAPAN), and the Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG). HARIMAU consisted of a radar-profiler network with meteorological Doppler radars of X-band (at Padang; e.g., Kawashima et al 2011;Mori et al 2011;Sakurai et al 2011;Kamimera et al 2012) and C-band (at Serpong near Jakarta; e.g., Wu et al 2013;Mori et al, 2018, personal communication), and wind profilers of L-band (at Pontianak, Manado, and Biak; e.g., Tabata et al 2011aTabata et al , 2011b. A large very high frequency (VHF) wind profiler called the Equatorial Atmosphere Radar (EAR) located at Kototabang (e.g., Fukao 2006;Shibagaki et al 2006;Seto et al 2009) was also included in the network.…”

“…In particular, HARIMAU2006, 2007 and 2011 were in the westernmost area of the IMC (Propinsi Sumatera Barat or West Sumatra Province), targeting the MJOs from the Indian Ocean and their modification (Yoneyama et al 2008(Yoneyama et al , 2013Kamimera et al 2012;Kubota et al 2015, with the MISMO and CINDY projects), the diurnal cycles of the major and smaller islands Kamimera et al 2012), and convective cloud structure and vertical coupling (Fukao 2006;Mori et al 2011;Kawashima et al 2006Kawashima et al , 2011Sakurai et al 2009Sakurai et al , 2011, with the Coupling Processes in the Equatorial Atmosphere (CPEA) project). HARI-MAU2008 and 2009 were performed over Kalimantan Island ).…”

“…Based on radar observations in Sumatera and Jawa, the rainfall intensity in a typical precipitating cloud system is stronger than 10 mm/h only in a small migrating area of (10 km) 2 , which has an echo top of about 10 km and a life time of roughly an hour (e.g., Kawashima et al 2006Kawashima et al , 2011Wu et al 2007Wu et al , 2013Sakurai et al 2009Sakurai et al , 2011Mori et al 2011 …”

Modulation of Diurnal Rainfall Cycle by the Madden-Julian Oscillation Based on One-Year Continuous Observations with a Meteorological Radar in West Sumatera

“…1). Previous studies used this radar (or another similar one) for periods up to one month Kawashima et al 2011;Fudeyasu et al 2011;Mori et al 2011). This study uses one-year continuous radar observations for the first time, and shows the modulations of the rainfall DC for each MJO phase.…”