Diurnal Land–Sea Rainfall Peak Migration over Sumatera Island, Indonesian Maritime Continent, Observed by TRMM Satellite and Intensive Rawinsonde Soundings

Abstract

The diurnal cycle of rainfall and its regional variation over Sumatera Island, Indonesian Maritime Continent, are examined using Tropical Rainfall Measuring Mission (TRMM) satellite precipitation radar (PR) and intensive rawinsonde sounding data. The TRMM PR sensor can detect raindrops directly, regardless of ground and cloud conditions, and can distinguish between convective and stratiform types of rainfall. Rainfall variation over this area was found to have the following characteristics: 1) convective rainfall with a broad peak between 1500 and 2000 LT predominates over the land region of Sumatera Island, whereas rainfall in the early morning, composed almost equally of stratiform and convective types, is predominant over the surrounding sea region. 2) A rainfall peak in the daytime and one in the nighttime migrate with time starting from the southwestern coastline of the island into the inland and offshore regions, respectively. The distance of each rainfall peak migration from the coastline is up to 400 km, and the average speed of migration is approximately 10 m s?1. 3) Using intensive rawinsonde sounding data, it was also found that remarkable diurnal variations of wind, humidity, and stability appear in the lower troposphere corresponding to the migrating rainfall peaks over both the inland and the coastal sea regions. The mechanism of the diurnal land?sea rainfall peak migration is discussed comprehensively using TRMM PR, intensive rawinsonde soundings, Geostationary Meteorological Satellite (GMS) data, objective reanalysis, and ground-based observation data. Finally, a crucial difference in rainfall peak migrating mechanisms is suggested between those toward the inland region in the daytime and the offshore region in the nighttime.