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

Abstract

One-year meteorological radar observations (from November 2006 to October 2007) over a region from the west coast of central Sumatera (Sumatra) through the Mentawai Strait (about 130-km width) to Siberut Island were analyzed, and modulation of rainfall diurnal cycle (DC) in the region by the Madden−Julian oscillation (MJO) was studied. The DC peaked in the afternoon over Sumatera and Siberut islands, and in the nighttime/early morning over Mentawai Strait between the islands. Over the strait, offshore (westward) migration of the DC peak was distinct when the MJO active phase was propagating eastward over the Indian Ocean, whereas the migration was indistinct after the active phase passed over Sumatera. When the MJO active phase was propagating eastward over the eastern Indian Ocean, the DC was amplified, and daily rainfall maximum tended to appear over western Sumatera including the strait. The DC peak originating from Sumatera reached Siberut, and the DC over Siberut had an additional, stronger rainfall peak after midnight.

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 ).…”

“…These feedback mechanisms may be suppressed, because the hydrologic and energy cycles close approximately on a diurnal time scale (including clear/dry land in the morning) over the IMC, and the standard features of ISVs/MJOs along the ITCZ over the Indian and Pacific Oceans (e.g., Julian 1971, 1994;Wheeler and Hendon 2004;Zhang 2005Zhang , 2013Yoneyama et al 2008Yoneyama et al , 2013 are greatly modified over the IMC. For example, passage of ISVs/MJOs over the IMC is shifted to the southern side of the equator, which gives a decrease in rainfall over the IMC from west to east (e.g., Nitta et al 1992;Shibagaki et al 2006;Hidayat and Kizu 2010;Fujita et al 2011;Kamimera et al 2012;Peatman et al 2014;Zhang and Ling 2017).…”

“…The rainfall (particularly over the sea rather than the land) at various locations over the IMC increases during the active/wet phase of ISVs/MJOs (e.g., Widiyatmi et al 2001;Murata et al 2002;Sakurai et al 2005Sakurai et al , 2009Sakurai et al , 2011Shibagaki et al 2006;Wu et al 2007Wu et al , 2013Hidayat and Kizu 2010;Mori et al 2011; Kamimera et al 2012;Peatman et al 2014). As a result, the onset and total rainfall amount of the rainy season over the IMC (in particular over the southern hemispheric part) are governed by the passage of active phases of ISVs/MJOs (see Fig.…”