Maritime continent coastlines controlling Earth’s climate

Abstract

During the Monsoon Asian Hydro−Atmosphere Scientific Research and Prediction Initiative (MAHASRI; 2006-16), we carried out two projects over the Indonesian maritime continent (IMC), constructing the Hydrometeorological Array for Intraseasonal Variation−Monsoon Automonitoring (HARIMAU; 2005-10) radar network and setting up a prototype institute for climate studies, the Maritime Continent Center of Excellence (MCCOE; 2009-14). Here, we review the climatological features of the world's largest "regional" rainfall over the IMC studied in these projects. The fundamental mode of atmospheric variability over the IMC is the diurnal cycle generated along coastlines by land−sea temperature contrast: afternoon land becomes hotter than sea by clear-sky insolation before noon, with the opposite contrast before sunrise caused by evening rainfall-induced "sprinkler"-like land cooling (different from the extratropical infrared cooling on clear nights). Thus, unlike the extratropics, the diurnal cycle over the IMC is more important in the rainy season. The intraseasonal, seasonal to annual, and interannual climate variabilities appear as amplitude modulations of the diurnal cycle. For example, in Jawa and Bali the rainy season is the southern hemispheric summer, because land heating in the clear morning and water vapor transport by afternoon sea breeze is strongest in the season of maximum insolation. During El Niño, cooler sea water surrounding the IMC makes morning maritime convection and rainfall weaker than normal. Because the diurnal cycle is almost the only mechanism generating convective clouds systematically near the equator with little cyclone activity, the local annual rainfall amount in the tropics is a steeply decreasing function of coastal distance (e-folding scale 100-300 km), and regional annual rainfall is an increasing function of "coastline density" (coastal length/land area) measured at a horizontal resolution of 100 km. The coastline density effect explains why rainfall and latent heating over the IMC are twice the global mean for an area that makes up only 4% of the Earth's surface. The diurnal cycles appearing almost synchronously over the whole IMC generate teleconnections between the IMC convection and the global climate. Thus, high-resolution (<< 100 km; << 1 day) observations and models over the IMC are essential to improve both local disaster prevention and global climate prediction.

Diurnal cycle over a coastal area of the Maritime Continent as derived by special networked soundings over Jakarta during HARIMAU2010

“…Mori et al (2004) further demonstrated the existence of diurnally migrating convective clouds along the coastal areas of Sumatra. This diurnal precipitation contributes to the climatological heavy rain near the coastline (e.g., Bergeman et al 2015;Ogino et al 2016;Ogino et al 2017;Yamanaka et al 2018). However, these features are still poorly reproduced by numerical simulations, especially in global circulation models with coarse horizontal resolutions (e.g., Sato et al 2009;Love et al 2011).…”

“…To tackle these questions, we conducted an intensive field campaign named HARIMAU2010 in which we deployed a sounding network and a C-band radar around Jakarta to capture the detailed spatiotemporal variations of the atmospheric states and precipitation features for approximately 1 month (January-February 2010; for additional details, please see Mori et al 2018 andYamanaka et al 2018). Utilizing the obtained sounding data, including the first-ever 2-week-long 8 times/day networked soundings over the MC, the present study aims to estimate the heat and moisture budgets and to combine these results with the radar-derived precipitation morphology to reveal the thermodynamic impacts of the diurnal cycle.…”

The typhoon-induced drying of the Maritime Continent

“…may help in forecasting the onset and duration of the dry season over the Maritime Continent. Consequently, forecasting TC activity can help improve, at least partially, the forecasts for all of the processes associated with the Maritime Continent circulation (55)(56)(57)(58)(59)(60).…”

Spatial and seasonal variability of clouds over the southwest Indian Ocean based on the DARDAR mask product

“…Many studies have been carried out in the northern part of the Indian Ocean basin (Dey et al, 2015), in particular to study the Indian monsoon (Rajeevan et al, 2013;Das et al, 2017). The northeastern Indian Ocean is well documented due to the presence of the Maritime Continent (Yamanaka et al, 2018) and to the strong influence of the Madden-Julian Oscillation (Riley et al, 2011;Sakaeda et al, 2017;Hung and Sui, 2018). However, it is important to consider the ocean as a whole as it is rather in the southern part of the basin that the positioning of the Mascarene High will partly drive the SIOD (Terray et al, 2003).…”