Abstract
This paper uses the Argo sea surface salinity (SSSArgo) before and after the passage of 25 tropical cyclones (TCs) in the Bay of Bengal from 2015 to 2019 to evaluate the sea surface salinity (SSS) of the Soil Moisture Active Passive (SMAP) remote sensing satellite (SSSSMAP). First, SSSArgo data were used to evaluate the accuracy of the 8-day SMAP SSS data, and the correlations and biases between SSSSMAP and SSSArgo were calculated. The results show good correlations between SSSSMAP and SSSArgo before and after TCs (before: SSSSMAP = 1.09SSSArgo−3.08 (R2 = 0.69); after: SSSSMAP = 1.11SSSArgo−3.61 (R2 = 0.65)). A stronger negative bias (−0.23) and larger root-mean-square error (RMSE, 0.95) between the SSSSMAP and SSSArgo were observed before the passage of 25 TCs, which were compared to the bias (−0.13) and RMSE (0.75) after the passage of 25 TCs. Then, two specific TCs were selected from 25 TCs to analyze the impact of TCs on the SSS. The results show the significant SSS increase up to the maximum 5.92 psu after TC Kyant (2016), which was mainly owing to vertical mixing and strong Ekman pumping caused by TC and high-salinity waters in the deep layer that were transported to the sea surface. The SSSSMAP agreed well with SSSArgo in both coastal and offshore waters before and after TC Roanu (2016) and TC Kyant (2016) in the Bay of Bengal.
Highlights
The Bay of Bengal (BoB) is a semi-enclosed basin and strongly influenced by the seasonally reversing monsoon winds
The results indicate that most of correlations between SSSArgo and SSSSMAP before and after 25 tropical cyclones (TCs) were relatively high
Results show that the SSSSMAP had a high correlation with the in situ salinity observations measured by Argo with considerable bias
Summary
The Bay of Bengal (BoB) is a semi-enclosed basin and strongly influenced by the seasonally reversing monsoon winds. The Bay receives a large quantity of freshwater from both rainfall and river runoff of the bordering countries [1]. The sea surface salinity (SSS) is very low in the northern. The influx of freshwater into the BoB forms obvious seasonal variations in the horizontal salinity gradient in the northern bay [2,3]. It is well known that TCs can induce dramatic physical processes (strong mixing and upwelling) in the upper ocean, which has a large impact on sea surface temperature, SSS, chlorophyll concentration, dissolved oxygen and so on [4,7,8,9,10,11,12,13]. The SSS can be affected by the TC-induced physical processes (strong mixing and Ekman pumping) and the large rainfall. Based on Aquarius and Soil Moisture and Ocean Salinity (SMOS) salinity observations, Water 2020, 12, 2975; doi:10.3390/w12112975 www.mdpi.com/journal/water
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