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Uncertainty of Aquarius sea surface salinity retrieved under rainy conditions and its implication on the water cycle study
Author(s) -
Tang Wenqing,
Yueh Simon H.,
Fore Alexander G.,
Hayashi Akiko,
Lee Tong,
Lagerloef Gary
Publication year - 2014
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2014jc009834
Subject(s) - argo , sss* , environmental science , scatterometer , radiometer , climatology , precipitation , atmospheric sciences , stratification (seeds) , special sensor microwave/imager , meteorology , remote sensing , wind speed , brightness temperature , geology , microwave , mathematics , physics , seed dormancy , mathematical optimization , germination , botany , dormancy , biology , quantum mechanics
The uncertainty of Aquarius sea surface salinity (SSS) retrieved under rain is assessed. Rain not only has instantaneous impact on SSS but also interferes with the microwave remote sensing signals, making the task to retrieve SSS under rainy conditions difficult. A rain correction model is developed based on analysis of the L‐band radiometer/scatterometer residual signals after accounting for roughness due to wind and flat surface emissivity. The combined active passive algorithm is used to retrieve SSS in parallel with (CAP_RC) or without rain correction (CAP). The CAP bias against individual ARGO floats increases with rain rate with slope of −0.14 PSU per mm h −1 , which reduced to near zero in CAP_RC. On the global monthly basis, CAP_RC is about 0.03 PSU higher than CAP. RMSD against ARGO is slightly smaller for CAP_RC than CAP. Regional biases are examined in areas with frequent rain events. As expected, results show that ΔSSS (CAP_RC‐CAP) is highly correlated with the seasonal precipitation pattern, reaching about 0.2–0.3 PSU under heavy rain. However, ΔSSS shows no correlation with the difference pattern between ARGO and CAP or CAP_RC. This, along with regional analyses, suggests that the difference between ARGO and Aquarius' SSS is likely caused by the different spatial and temporal sampling, in addition to near surface stratification depicted by radiometer and ARGO at different depths. The effect of ΔSSS on water cycle in terms of mixed‐layer salt storage tendency is about 10% in areas where evaporation‐minus‐precipitation is the dominant process driving the variability of near surface salinity.