Seasonal and interannual variation of North Pacific Subtropical Mode Water in 2003–2006 |
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| Authors: | Eitarou Oka |
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| Institution: | (1) Ocean Research Institute, The University of Tokyo, Nakano-ku, Tokyo 164-8639, Japan |
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| Abstract: | Temperature and salinity data from 2003 through 2006 from Argo profiling floats have been analyzed to examine the formation
and circulation of the North Pacific Subtropical Mode Water (STMW) and the interannual variation of its properties over the
entire distribution region. STMW is formed in late winter in the zonally-elongated recirculation gyre south of the Kuroshio
and its extension, which extends north of ∼28°N, from 135°E to near the date line. The recirculation gyre consists of several
anticyclonic circulations, in each of which thick STMW with a characteristic temperature is formed. After spring, the thick
STMW tends to be continually trapped in the respective circulations, remaining in the formation region. From this stagnant
pool of thick STMW, some portion seeps little by little into the southern region, where southwestward subsurface currents
advect relatively thin STMW as far as 20°N to the south and just east of Taiwan to the west. The STMW formed in the recirculation
gyre becomes colder, less saline, and denser to the east, with an abrupt change of properties across 140°E and a gradual change
east of 140°E. The STMW formed east of 140°E exhibits coherent interannual variations, increasing its temperature by ∼1°C
from 2003 through 2006 and also increasing its salinity by ∼0.05 from 2003 through 2005. These property changes are clearly
detected in the southern region as far downstream as just east of Taiwan, with reasonable time lags. |
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| Keywords: | North Pacific Subtropical Mode Water seasonal variation interannual variation Argo |
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