A Wide-Spread Freshening During Passage of a Typhoon Captured By Aquarius: A Case Study
[11-Nov-2014] Abe, H. and Ebuchi, N.
Presented at the 2014 Aquarius/SAC-D Science Team Meeting
The present study examined ocean salinity responses to a passage of a typhoon using Aquarius Level-2 swath SSS data and Level-3 weekly-averaged SSS data. We targeted at one of typhoons generated in the east of Philippines in 2012; after the formation, it moved to north-east direction by crossing western North Pacific basin, passed through south of Japan, and went into central North Pacific. Analyses of the Aquarius data were conducted by focusing on a region near Japan.
We picked up three of the Aquarius subtracks at nearly the same locations in order to examine Aquarius SSS 1) before, 2) during, and 3) after the passage of the typhoon. In case 1), typical value of the Aquarius along-track salinity was 34 ? 35 psu in this region. In case 2), Aquarius captured a freshened sea water with a value of less than 30 psu, which is quite low compared to the typical value. In case 3), the lower-value SSS was recovered up to the normal level. This SSS freshening signal, found in the Level-2 data, was also detected even in the Level-3 weekly-averaged data. The Level-3 Aquarius SSS averaged over 7 days for a peak phase of the typhoon, was lower by 1 psu than that in a week ahead of the peak phase.
According to the analysis using satellite data from TRMM/TMI, a precipitation event was observed at the location where the negative temporal change of the weekly-averaged SSS was detected. Evaporation minus precipitation flux (or E-P flux), calculated using the data, was -150 mm/week over the negative change area. This fresh water has to be mixed with sea water within an ocean mixed layer with the scale of 5 m, in order to explain 1 psu of SSS freshening.