Kuroshio Extension Front
Has Strong Seasonal Impacts on Clouds
Hiroki Tokinaga1, Youichi Tanimoto2,3, Shang-Ping Xie1, Takeaki Sampe1, Hiroyuki Tomita4, Hiroshi Ichikawa4
1IPRC, 2Hokkaido Univ., 3FRCGC/JAMSTEC, 4IORGC/JAMSTEC
Winter
Summer
Air-sea temp. difference
(e)
(a)
(b)
Frequency of sea fog
(f)
(c)
(d)
(a) Surface heat flux, (b) cloud liquid water, (c) high-pass filtered SLP, and (d)
cloud top occurrence between 500-700hPa in December-February. Contours are
SST at 2ºC intervals.
In winter, intense turbulent heat release from the ocean takes place on
the southern flank of the Kuroshio Extension (KE) front (Fig. a), where
cloud liquid water shows a local maximum and the cloud top
penetrates above the marine atmospheric boundary layer (MABL) and
reaches the mid-troposphere (Fig. d). Our results suggest a sea level
pressure mechanism, where temperature gradient in the MABL
induces strong surface wind convergence on the southern flank of the
KE front, deepening the clouds there (Fig. c).
(e) Air-sea temperature difference and (f) sea-fog
frequency under the southerly winds in June.
Dashed line is 0ºC contour of air-sea temp. difference.
In summer, sea fog frequently occurs on the
northern flank of the KE front and subarctic fronts
under southerly warm advection that suppresses
surface heat flux and stabilizes the surface
atmosphere (Fig. f). Sea fog is infrequently observed
over the KE front even under southerly conditions
because the warm ocean current weakens
atmospheric stratification and promotes vertical
mixing (Fig. e).