Propagation of the Madden–Julian Oscillation through the Maritime Continent and scale interaction with the diurnal cycle of precipitation

Abstract

The convectively active part of the Madden-Julian Oscillation (MJO) propagates eastward through the warm pool, from the Indian Ocean through the Maritime Continent (the Indonesian archipelago) to the western Pacific. The Maritime Continent's complex topography means the exact nature of the MJO propagation through this region is unclear. Model simulations of the MJO are often poor over the region, leading to local errors in latent heat release and global errors in medium-range weather prediction and climate simulation.Using 14 northern winters of TRMM satellite data it is shown that, where the mean diurnal cycle of precipitation is strong, 80% of the MJO precipitation signal in the Maritime Continent is accounted for by changes in the amplitude of the diurnal cycle. Additionally, the relationship between outgoing long-wave radiation (OLR) and precipitation is weakened here, such that OLR is no longer a reliable proxy for precipitation. The canonical view of the MJO as the smooth eastward propagation of a large-scale precipitation envelope also breaks down over the islands of the Maritime Continent. Instead, a vanguard of precipitation (anomalies of 2.5 mm day −1 over 10 6 km 2 ) jumps ahead of the main body by approximately 6 days or 2000 km. Hence, there can be enhanced precipitation over Sumatra, Borneo or New Guinea when the large-scale MJO envelope over the surrounding ocean is one of suppressed precipitation.This behaviour can be accommodated into existing MJO theories. Frictional and topographic moisture convergence and relatively clear skies ahead of the main convective envelope combine with the low thermal inertia of the islands, to allow a rapid response in the diurnal cycle which rectifies onto the lower-frequency MJO. Hence, accurate representations of the diurnal cycle and its scale interaction appear to be necessary for models to simulate the MJO successfully.

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).…”

“…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.…”

Diurnal cycle of the South Pacific Convergence Zone in 30 years of satellite images

“…Houze, 1997; Tian et al, 2006;Peatman et al, 2013;Oh et al, 2012] or decreasing [Sui and Lau, 1992] the strength of the diurnal cycle. To further explore this, the diurnal cycle in Regions 3, 5, and 7 will be examined in detail during different phases of the MJO.…”

Modes of vertical thermodynamic and wind variability over the Maritime Continent

“…Among these are the diurnal cycle of convection, the Madden-Julian Oscillation (MJO; Zhang, 2005), equatorial waves, seasonal monsoons (Misra and Li, 2014), progression of the Intertropical Convergence Zone (ITCZ), the El Niño-Southern Oscillation (ENSO), as well as a host of mesoscale and local circulations. Models have difficulty realistically simulating the propagation of tropical waves through the region in part due to the interactions across scales (Peatman et al, 2014(Peatman et al, , 2015. They have also proven largely unable to reproduce the diurnal cycle of convection, which exhibits a nocturnal maximum over the ocean (Chen and Houze, 1997;Sui et al, 1997;Yang and Slingo, 2001;Dai, 2001).…”