Subtropical Front Anchors Deep Cloud Band

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Subtropical Front Anchors Deep Cloud Band F.
Kobashi1, S.-P. Xie2, N. Iwasaka1, and T.
Sakamoto3 (J. Climate 2008) 1Tokyo U. of Marine
Sci. and Tech. 2IPRC 3JAMSTEC-FRCGC
Negative wind stress curl dominates the North
Pacific subtropical ocean gyre for most of the
year. During AprilMay, however, QuikSCAT
observations reveal a band of positive wind
stress curl in the middle of the gyre around
22oN. Anchored by the sea surface temperature
(SST) along the subtropical front, the band
hovers over a column of high water vapor content
(upper panel). An atmospheric reanalysis product
shows that during AprilMay mid-latitude weather
disturbances trigger sub-synoptic cyclones along
the front, which give rise to positive wind curls
and a deep upward motion that moistens the entire
troposphere (lower panel). The North Pacific
subtropical front is unique among major SST
fronts in that the SST on its southern flank is
greater than 27oC so that the surface water is
warm enough to support deep convection.
Surface wind stress (N/m2) local minimum, and
precipitable water (color in mm) meridional
maximum along SST front (contours in oC)
At the subtropical front at 22oN, deep upward
motion with increased moisture (color in g/kg)
during positive surface wind curls.