High Resolution Rain Impact Model (HiRIM): An Oceanic Salinity Stratification Study

Maria Marta Jacob, Universidad Nacional de Cordoba, Facultad de Matematica, Astronomia y Fisica, Cordoba, Argentina, Kyla Drushka, University of Washington, Applied Physics Laboratory, Seattle, WA, United States, William Asher, University of Washington Seattle Campus, Seattle, WA, United States and W. Linwood Jones, University of Central Florida, Central Florida Remote Sensing Laboratory, Orlando, FL, United States
Abstract:
When rain falls over the ocean, freshwater deposited on the ocean surface, typically over a short period of time (< 1h), produces buoyant fresh layers that in time are integrated downward into the ocean through advection and mixing. Therefore, when rain is present, there is often a salinity gradient in the top few meters of the ocean, making comparisons with bulk salinity and satellite-measured sea surface salinity (SSS) difficult. In both precipitation- and evaporation-dominated regions, extrapolating in situ point measurements to the 40 - 100 km scales captured by satellites remains a challenge. Thus, using the satellite SSS measurements to estimate the ocean salinity at 5 – 10 m depth may not be reliable in rainy regions.

Our team has previously used CMORPH precipitation data to develop a Rain Impact Model (RIM) to predict the change of SSS due to rainfall for the Aquarius, SMOS and SMAP L-band instruments. The RIM model applies a 1-D turbulent diffusion model to the ocean salinity measurements from HYCOM and rain from the CMORPH product to estimate changes in SSS for 24 h prior to the satellite observation time and to estimate the SSS dilution produced by rainfall at the time of the satellite observation. RIM SSS and satellite SSS were found to be well correlated.

Here, we extend our previous investigation of rain-induced sea surface salinity stratification using our new High Resolution Rain Impact Model (HiRIM). Improving on the original RIM, HiRIM uses a diffusion coefficient that depends on both wind speed and rain rate. HiRIM model salinity is output at several depths in the upper 10 m, in 0.5 h time-steps, at the CMOPRH spatial resolution of 8 km. These near-surface salinity profiles are compared to the numerous in situ salinity measurements collected during the SPURS-2 field experiment at a variety of depths. With this product it will be possible to identify the occurrence of salinity stratification for the current SMAP and SMOS missions.

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