Decomposing mesoscale convective systems and isolated convection in tropical South America

Abstract:

Mesoscale convective systems (MCSs) and isolated convective cells are both key contributors to precipitation in tropical South America. Particularly, propagating squall lines from the Atlantic coast have a strong influence over the annual average diurnal cycle of rainfall, while this influence is weaker during the dry-to-wet transition season. To better understand their respective roles in shaping the regional water cycle, including the seasonal and diurnal variations, we conducted a decomposition based on 20-year satellite precipitation retrievals. Compared with the diurnal cycle of MCS rainfall which broadly follows the distance away from squall line origination, non-MCS rainfall has a more uniform diurnal peak in the local afternoon across most of the region. Both types of precipitation are nearly absent during the dry season, but the precipitation due to isolated convection increases earlier before the wet season onset as well as the increase in MCS precipitation. Further examination suggests that surface conditions have a stronger connection with isolated convection than MCSs. An obvious example is given by the Amazon River, over which the non-MCS rainfall is substantially suppressed compared with its surroundings. This rainfall reduction has been shown to have a good linear correlation with the surface temperature pattern. The MCS rainfall is only slightly enhanced over the river, if any. The isolated convective cells triggered ahead of squall line fronts will also be addressed. In addition, this satellite-based precipitation decomposition will be further combined with ground-based measurements made during the 2014-2015 GoAmazon experiment.