Rainfall imprint on SMOS and SMAP Sea Surface Salinity
Abstract
Two L-Band (1.4GHz) microwave radiometer missions, Soil Moisture and Ocean Salinity (SMOS) and Soil Moisture Active and Passive (SMAP), currently provide sea-surface salinity (SSS) measurements. At this frequency, salinity is measured in the first centimetre below the sea surface, which makes it very sensitive to the presence of fresh water lenses linked to rain events. A relationship between salinity anomaly (ΔS) and rain rate (RR) is derived in the Pacific intertropical convergence zone from SMOS and SMAP SSS measurements, and the RR from the Special Sensor Microwave Imager/Sounder (SSMIS). We look at the robustness of the relationship in various areas. It is then used to estimate RR from SMOS and SMAP SSS measurements. By applying this algorithm over the global ocean between 30°S and 30°N, we found that the rain imprint is the dominant factor affecting SMOS and SMAP variability at small temporal scale, except in river plumes (Amazon, Mississippi, etc.) and in regions with high mesoscale variability. Our study allows to identify the observed difference between Argo products and satellite salinity that are due to the impact of rain on the satellite salinity in the first centimetre measured.