In-situ observations of Kuroshio Extension's influence on the atmosphere

Observational and modeling studies indicate that over the Kuroshio-Oyashio Extension the deep ocean mixed layer in winter enables ocean subsurface anomalies, often remotely forced, to affect SST variability. Recent satellite observations further show that SST variability exerts a significant influence on local surface wind.

We have carried out ship-board atmospheric soundings in the region along with concurrent ocean hydrographical observations, twice during the winter of 2003-04 and once in June-July 2005. Over a combined duration of 70 days, a total of 240 GPS-sondes were released, resulting in vertical profiles of temperature, humidity, pressure and wind velocity across the Kuroshio Extension (KE) front. On the 2005 summer cruise, ceilometer observations were also carried out.

The winter observations show a clear correlation of the depth and vertical shear of the atmospheric mixed layer with surface static stability: the mixed layer deepens with weak shear when the sea-air surface temperature difference is large. This is consistent with the satellite observations that surface winds are higher over the warm Kuroshio Current and warm rings as high SST destabilizes the surface atmosphere and the enhanced mixing brings faster wind down from aloft.

Summer North Pacific climate is characterized by arobust and extensive low-cloud deck north of the KE. In the summer of 2005, the KE front in SST is well defined, centered along 36N with a temperature difference of~4 C over the 100 km wide front. Our summer soundings capture this cloud deck and the capping inversion at around 1 km height. In addition sea fog is occasionally observed near the SST front and capped by a surface inversion, often when the wind is from the south. The talk will present further analysis of the summer soundings and relate their variations to the underlying SST structures.