Diurnal Convection Peaks over the Eastern Indian Ocean off Sumatra during Different MJO Phases

Abstract

The authors investigated diurnal convection peak characteristics over the eastern Indian Ocean o¤ the island of Sumatra during di¤erent phases of the Madden-Julian oscillation (MJO). During MJO phases 2 to 3 (P2 and P3) defined by Wheeler and Hendon (2004), prominent diurnal variation in convection was observed by satellites when moderate low-level westerly winds were dominant over the eastern Indian Ocean. The diurnal convection peaks were prominent over the island of Sumatra in the evening, while migrations of the convection toward the Indian Ocean were observed in the early morning. By using the Global Positioning System around the western region o¤shore of Sumatra, a significant reduction in water vapor was observed from evening until midnight, compensating for the upward motion over the island. During midnight to early morning, the water vapor increased in the western o¤shore region as the convections migrated from the island. This prominent diurnal variation confirmed the result from a numerical experiment by Miura et al. (2007) using the Nonhydrostatic ICosahedral Atmospheric Model (NICAM).During P2 to P3, the atmosphere over the eastern Indian Ocean contains abundant water vapor, while the Maritime Continent is fairly well heated by solar radiation under calm conditions. This situation should be favorable for the development of two diurnal convection peaks: the evening convection over the land induced by solar radiative heating and the midnight convection over the ocean triggered by convergence of the low-level westerly wind and the land breeze.

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

“…3). These two peaks were consistent with rain gauge and Global Positioning System (GPS) humidity observations (peaks around 02 and 14 LT), on Siberut ) and on other Mentawai islands (Fujita et al 2011). This study proves that the nighttime peak over Siberut during phases 8 and 1−4 originates from the peak after sunset on the west coast of Sumatera.…”

“…Their maxima are from afternoon to midnight over land, and from nighttime to early morning over sea (e.g., Nitta and Sekine 1994;Mori et al 2004;Sakurai et al 2005). These features, as well as the relationships between the MJO over the Indian Ocean and the DCs over the IMC, have been studied mainly based on satellite observations (e.g., Sui and Lau 1992;Murata et al 2006;Shibagaki et al 2006;Tian et al 2006;Ichikawa and Yasunari 2007;Fujita et al 2011). In western Sumatera (Sumatra), which is at the western edge of the IMC and is the place where the MJO first comes ashore, annual rainfall reaches 2,600−6,300 mm (year) −1 over land , from surface rain gauges).…”

“…Convective clouds with DC migrate between land and sea. Offshore (westward) migrations of the clouds can be observed in all seasons (Sakurai et al 2005, with the Geostationary Meteorological Satellite, GMS), and are activated when the MJO active phase arrives over Sumatera (Fujita et al 2011, with the TRMM and geostationary satellites including the GMS).…”

Maritime continent coastlines controlling Earth’s climate

“…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).…”

Role of Maritime Continent Convection during the Preconditioning Stage of the Madden-Julian Oscillation Observed in CINDY2011/DYNAMO

“…Over Sumatra Island, diurnal cycle of the convection was dominant and nocturnal convection tended to propagate westward from Sumatra Island (Mori et al 2004;Wu et al 2008). Nocturnal westward propagating convection was activated when the active phase of the MJO was located in the Indian Ocean (Fujita et al 2011;Kamimera et al 2012). They considered the influence of the MJO on the convection in the maritime continent; however, they did not discuss the impact of maritime continent convection on the MJO.…”