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Correlative Analysis of Aquarius, Grace and River Discharge Data Indicating the Change of Water Cycle In the India Subcontinent
[28-Nov-14] Yueh, S., Tang, W., Fore, A., Hayashi, A., Lee, T., Bindlish, R., and Jackson, T.
Presented at the 2014 Ocean Salinity Science and Salinity Remote Sensing Workshop
Aquarius is a combined passive/active L-band microwave instrument developed to map the sea surface salinity (SSS) field from space. The accuracy of Aquarius monthly averaged SSS product derived from the Combined Active and Passive (CAP) algorithm has been estimated to be about 0.1 to 0.2 psu Root-Mean-Square (RMS) between 40 degrees N and 40 degrees S through comparison with the Argo gridded dataset produced by the Asia-Pacific Data- Research Center (APDRC) and tropical moorings. We find that the regions with larger discrepancy include the ITCZ and near the outflow of major rivers, such as the Ganges, where the surface stratification due to precipitation or river discharge appears to be playing a significant role. In addition to the salinity product, Aquarius’ radiometer data have been used to produce the surface soil moisture globally. We find that the change of soil moisture over the India subcontinent clearly correlates with the timing of India Monsoon, which produces significant precipitation between June and September. We compared the Aquarius surface soil moisture with the total land mass change derived from the GRACE mission data and find good correlation between them at a few hundred km scale. We analyzed the time series of Aquarius soil moisture over the India subcontinent, river discharge (Ganges River) and Aquarius surface salinity in the Bay of Bengal (BOB). We find excellent correlation between the river discharge and soil moisture throughout all seasons. However we find that the change of surface salinity in the BOB seems to fall behind the change of soil moisture and river discharge by about 2 months before the monsoon season starts in June. This suggests that lighter precipitation starting as early as March does not have much impact on the surface salinity in the BOB. Once the heavier precipitation starts in June, the surface salinity in the BOB shows a rapid drop and the river discharge continues to rise until September when the monsoon season ends. We also compared the time series of Aquarius surface salinity with the Argo APDRC gridded product in the BOB. The comparison suggests that the Aquarius surface salinity in general agrees with the APDRC to within about 0.5 psu off the monsoon season, while during the monsoon season the Aquarius surface salinity tends to be below the APDRC by 1 to 3 psu. The larger discrepancy in August and September is likely due to the surface stratification resulting from rain or river discharge. Our correlative analysis indicates the change of surface salinity in the BOB clearly reflect the precipitation during the monsoon. However, the evaporation appears to dominate the change of surface salinity from March to May.

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