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Jacob, M., Santos-Garcia, A., Jacob, M., Jones, L., and Asher, W. (13-Nov-14)

This paper presents results of a recent empirical investigation into the impact of rain on the Aquarius (AQ) Sea Surface Salinity (SSS) measurements. Results demonstrate that AQ SSS measurements are realistic characterizations of a transient dilution of the surface salinity, but they are NOT representative of the bulk salinity at 5 m depth given by HYCOM. We believe that, during recent rain events, careful interpretation of AQ Level-2 (L-2) data is required, and as a result, the Rain Impact Model (RIM) product has been developed. It is available to AQ science users to promote the understanding of the relationship between precipitation and the corresponding AQ SSS measurement. This paper presents the description of RIM and comparisons between RIM and AQ L-2 SSS are presented for a number of rain events along the Pacific ITCZ (Inter-tropical Convergence Zone). Results demonstrate high correlation between RIM and AQ SSS for moderate to strong rain events that occurred within a few hours of the AQ observation time.

The RIM model is based on the temporal superposition of rain events (integrated rain history for the last 24 hours) using a one-dimensional stratification model and HYCOM as initialization. It estimates SSS in a quarter degree spatial resolution and integrates over the AQ IFOV (100 km) using a weighted average based on the antenna beam efficiency. Thus, the RIM predicts the modeled surface salinity that can be compared to the observed SSS as an overly to the AQ L-2 data product. In addition, the RIM provides the corresponding rain beam-fill fraction and the probability of salinity stratification. This latter parameter can be used as a "rain impact" quality flag to identify SSS that are affected by near surface stratification.