Characteristics of Convective Properties during Madden–Julian Oscillation (MJO) over the Maritime Continent Using Numerical Simulations at a Cloud-Permitting Scale with Assimilation of Satellite, Radar, and In Situ Observations

The Madden-Julian Oscillation (MJO) is an eastward-propagating convective cluster with intraseasonal variability (30-60 day) in the tropics. Its interaction with mesoscale convective systems (MCSs) over the Maritime Continent (MC) region is one of the main drivers of high-impact weather and climate in the region. However, due to the lack of observations and coarse resolution of available global reanalyses, understanding the processes that control the interaction between MJO and MCSs is challenging. The wind fields, precipitation, and surface fluxes over the MC region are commonly uncertain.

This study utilizes the mesoscale community Weather Research and Forecasting (WRF) model and its data assimilation system to investigate the diurnal variations of the small- and meso-scale convective systems and their associated winds and precipitation over Maritime Continent (MC) during Madden-Julia Oscillation (MJO) events. The variability of the convective systems, precipitation, and winds on the diurnal and synoptic scales and their interactions with the MJO propagation are characterized. The relationship between diurnal variations of winds and precipitation over the MC region as well as the effects of local scale land-sea breezes and orography on convective system initiation, evolution, and propagation are investigated.

Specifically, data assimilation is performed with the NCEP Gridpoint Statistic Interpolation (GSI) assimilation system at a cloud permitting scale over the MC region. Available in-situ, satellite and radar data are assimilated. The satellite data from new sensors, such as ocean surface winds and fluxes from the recent NASA Cyclone Global Navigation Satellite System (CYGNSS) mission are also assimilated into WRF model. Numerical simulations during the January to February 2018 MJO event within the Years of Maritime Continent (YMC) field campaign are conducted. The realism of simulated MCSs and MJO propagation based on the assimilation of conventional and satellites, especially the new CYGNSS ocean surface winds as well as radar data over the MC region are examined. The land/sea breezes related to the diurnal cycles of winds and precipitation are analyzed over both the ocean and land in the MC region. The high-resolution regional analysis and simulations provide new insights about the properties of MCSs (e.g., winds, precipitation, surface fluxes, and boundary layer structure) in the region and their interactions with MJO. Details will be reported at the conference.