Relationship between the direction of diurnal rainfall migration and the ambient wind over the Southern Sumatra Island

Abstract

This study investigates the climatological relationship between diurnal rainfall migration and the ambient wind over the southern Sumatra by using observation and reanalysis of 15 years of data from the Tropical Rainfall Measuring Mission satellite precipitation radar. When winds in the lower troposphere (1000-500 hPa) are westerly, convective rainfall systems migrate eastward, while rainfall systems dominated by stratiform precipitation propagate to the west in association with mid-upper level easterly winds. When the winds are easterly throughout the troposphere, both convective and stratiform precipitation systems propagate only to the west. Rainfall system migration appears to be generally consistent with ambient zonal wind. It is suggested that the advection by background wind is, in general, a dominant component of the propagation mechanism of diurnal rainfall.

Intraseasonal Variability of the Diurnal Cycle of Precipitation in the Philippines

“…The authors argued that westward propagation was due to the upper-tropospheric easterlies, and noted that eastward propagation occurs most frequently when the low level flow has an easterly component, similar to the hypothesis of Mori et al (2004). Similarly, Yanase et al (2017) used composites from nearly two decades of satellite retrievals to argue that when the entire profile consists of easterlies, convective and stratiform rainfall propagate westward. However, when lower-tropospheric winds are westerly, convective systems are advected eastward, while stratiform precipitation is still sheared off to the west.…”

“…There is some evidence of propagation on the east side of the Philippines too, as indicated by times getting progressively later heading further from land, but this does not appear to be as prominent as progression on the west side. Studies covering other regions of the global tropics have also indicating a preference for westward propagation offshore for Borneo and Sumatra (Mapes et al 2003a, Mori et al 2004, Sakurai et al 2005, Ichiwaka and Yasunari 2006, Tulich and Kiladis 2012, Yanase et al 2017.…”

“…Fujita et al (2011) used a collection of datasets and models from various sources to show that the diurnal cycle is most active when weak westerlies are present, or just before the large-scale convection arrives. Similar to New Guinea, convection propagates exclusively westward when the MJO background flow is easterly, and in both directions when the lower-tropospheric flow is westerly (Sakurai et al 2005, Yanase et al 2017. Oh et al (2012) argued that the decline in the diurnal cycle after MJO onset is partially related to the prevailing westerlies disrupting the convergence related to the sea-breeze circulation.…”

“…Upper tropospheric winds at 250-hPa in this region are out of the east-northeast, with a speed maximum over the equator. These winds are important for shearing the anvils of storms (Ackerman et al 1988) as well as regulating the offshore propagation of storms and mesoscale convective systems on diurnal time-scales (Mori et al 2004, Sakurai et al 2005, Yanase et al 2017, a major focus of this thesis.…”

Detecting and Tracking Coastal Precipitation in the Tropics: Methods and Insights into Multiscale Variability of Tropical Precipitation

“…At night, the diurnal sea breeze reverses into a land breeze. This land breeze and other processes such as gravity waves triggered by convection over the island are responsible for the offshore propagation of land convection over the surrounding ocean at night (Saito et al 2001;Mori et al 2004;Qian 2008;Love et al 2011;Hassim et al 2016;Vincent and Lane 2016;Li et al 2017;Yanase et al 2017;Coppin and Bellon 2019a,b).…”