Estimation of Fresh-Water Flux and its Impact to the Oceanic Stratification on the Coastal Heavy Rain in the Maritime Continent: A Case Study using R/V Mirai Shipboard Polarimetric Radar

An inter-agency project "Years of the Maritime Continent (YMC)" is on-going to investigate mechanism and impact of the processes over the Maritime Continent. As a pilot study of YMC, we deployed a special observation network, including the research vessel (R/V) Mirai and land-based observations, over the western coast of Sumatra Island where the coastal heavy rainfall were observed diurnally. During 25-days of the special observation in November to December 2015, we captured the detail of the diurnal convection and oceanic stratification, and their modulation by the Madden-Julian Oscillation (MJO).

In this study, we utilize the data from the shipboard C-band polarimetric radar onboard R/V Mirai to estimate the fresh-water flux into the ocean (and land). The diurnal heavy rain, weak wind, and oceanic stratification in surface tens meters were observed before onset of the active phase of the MJO. In contrast during the active phase of MJO, the eastward-propagating non-diurnal rain, strong westerly wind, and well-mixed oceanic profiles were captured.

To estimate the impact of the local diurnal heavy rainfall to the ocean, we utilized KDP-based rainfall estimation to quantify the local fresh-water flux. The KDP and ZH data were quality-controlled by the method of Geng and Katsumata (presented in this conference). The estimated rain parameters are validated by the in-situ disdrometers / raingauges at land sites which distanced approximately 50-km from the vessel, along with the onboard disdrometers / raingauges. The estimated rainfall are compared to the oceanic parameters (salinity, temperature, etc.) to investigate the impact of local rainfall to the oceanic stratification.