Meetings: Documents

Evaluation of Sea Surface Salinity Observed By Aquarius
[11-Nov-14] Abe, H. and Ebuchi, N.
Presented at the 2014 Aquarius/SAC-D Science Team Meeting
Sea surface salinity (SSS) fields from three different Aquarius products (Aquarius Official Release version 3.0 (V3.0), Combined Active-Passive (CAP) algorithm version 3.0, Remote Sensing Systems (RSS) test bed algorithm version 3) were evaluated by comparing them to in situ SSS measurements from Argo floats and tropical moored buoys, as well as with global gridded SSS fields produced by JAMSTEC and JMA/MRI.
Level-2 Aquarius SSS was collocated with in situ near-surface salinity with spatial and temporal separations of less than 200 km and 12 hours, respectively. In general, the Level-2 Aquarius SSSs showed good agreement with the Argo near-surface salinity. The root-mean-square (rms) difference was 0.42 psu, 0.52 psu, and 0.41 psu for the Aquarius V3.0, CAP, and RSS products, respectively. The same calculation was conducted using the near-surface salinity from tropical moored buoys. The rms difference was 0.35 psu, 0.39 psu, and 0.35 psu for each of the Aquarius products. In any of these cases, the CAP product had the largest rms difference. A significant SSS difference between ascending and descending paths was detected in all of the Aquarius products, although it has been reduced in the V3.0 and CAP V3.0 products.
Level-3 monthly-averaged Aquarius SSS was compared to the outputs from an ocean data optimal interpolation system produced by JAMSTEC and an ocean data assimilation system by JMA/MRI. The monthly-averaged SSSs were collocated at the same longitude-latitude grids with 1 degree spacing at each month. The Level-3 SSS products showed good agreement with the global gridded SSS field. A systematic negative bias was detected in the Asian Pacific in the Aquarius products. The V3.0 was biased positively (negatively) in the high (low) latitude while the CAP product was less biased. The rms difference, calculated for 40°S-40°N, was 0.26 psu for the V3.0. The CAP product showed a lower value of the rms difference, 0.22 psu, which is close to Aquarius mission goal.