[A-AS05] Large-scale moisture and organized cloud systems

[AAS05-P01] Reproducibility of precipitation diurnal cycle over tropical coastal regions in climate simulations of a global atmospheric cloud-system resolving model

*Satoru Yokoi¹, Yoshiyuki Kajikawa² (1.Japan Agency for Marine-Earth Science and Technology, 2.Kobe Univ.)

Keywords:precipitation diurnal cycle, NICAM-HighResMIP experiment, NICAM-AMIP experiment, shipborne observation

Diurnal cycle over tropical coastal regions is characterized by afternoon precipitation maximum over coastal land and evening offshore-ward migration of precipitation areas over coastal waters. Researchers have paid more attention to the latter and argued fundamental dynamics behind the migration. Existence of the migration behavior makes it necessary to perform global numerical simulation with explicit representation of cloud systems for examining influence of the diurnal cycle on the global circulation and impact of climate change. Recently, two sets of climate simulations have been performed using Nonhydrostatic Icosahedral Atmospheric Model (NICAM), which are called NICAM-AMIP and NICAM-HighResMIP. In this study, outputs of NICAM-AMIP with 14-km horizontal resolution (A14), and NICAM-HighResMIP with 14-km and 28-km resolutions (H14 and H28, respectively) are analyzed to examine how these experiments realistically represent precipitation diurnal cycle over the tropical coastal regions. We find that all the three simulations represent afternoon land precipitation, though precipitation maximum tends to lag several hours compared to satellite observations. The evening offshore migration is represented in H14 fairly well, although similar lag is also found. As triggering of new convections to the offshore side of existing ones by convective cold outflow is one of the candidate mechanisms for the offshore migration, we compare simulated cold outflow with shipborne observations off the west coast of Sumatra Island, where the offshore migration can be observed quite frequently. We find that, although all the three experiments underestimate the cold outflow strength compared with the observation, H14 represents the cold outflow strength closest to the observation.