Precipitation Estimates from SMOS Sea‐Surface Salinity. (7th August 2017)

• Record Type: Journal Article
• Authors: Supply, A.; Boutin, J.; Vergely, J.‐L.; Martin, N.; Hasson, A.; Reverdin, G.; Mallet, C.; Viltard, N.
• Is Part Of: Quarterly journal of the Royal Meteorological Society. Volume 144(2018)Supplement 1
• Page Start: 103
• Page End: 119
• Publication Date: 2017-08-07
• Subjects: IMERG -- ITCZ -- L‐band radiometry -- precipitation -- sea‐surface salinity anomalies -- SMAP -- SMOS; Meteorology -- Periodicals; 551.5
• DOI: 10.1002/qj.3110
• Languages: English
• ISSNs: 0035-9009

Abstract

Abstract : Two L‐Band (1.4 GHz) 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 SSS measurements and Special Sensor Microwave Imager/Sounder (SSMIS) RR. It is then used to develop an algorithm to estimate RR from SMOS SSS measurements. A heuristic function is developed to correct the SMOS‐estimated negative RR due to measurement noise. Correlation between SMOS and SSMIS RR and between SMOS and Integrated MultisatellitE Retrievals for GPM (IMERG) RR are high when SMOS and SSMIS passes are less than 15 min apart (r = 0.7 at 1° × 1° resolution), showing a good quality of SMOS RR retrievals. When the time shift between SMOS and SSMIS passes increases, the correlation between SMOS and IMERG RR diminishes. This suggests that L‐band radiometry can provide information complementary to GPM missions to improve RR products interpolated at high temporal resolution. The retrieval is successfully tested on SMAP SSS. We also check that our algorithm provides reliable estimates of RR when averaged at a monthly time‐scale. Abstract : Rain rate (RR) is derived in the Pacific intertropical convergence zone from SMOS SSS measurements. SMOS and SSMIS RR agree well when SMOS and SSMIS passes are less than 15 min apart (see an example on the figure below; r = 0.7 at 1° × 1° resolution). When the time shift between SMOS and SSMIS passes increases, the correlation between SMOS and IMERG RR diminishes. This suggests that L‐band radiometry can provide information to improve RR products based on morphing techniques.