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
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.
Negative wind stress curl dominates
the North Pacific subtropical ocean
gyre for most of the year. During
April–May, 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 April–May midlatitude 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.