Variability of the sub-polar front in the Japan/East Sea during winter 2009-2010

The temporal and spatial variability of the Subpolar Front (SPF) in the Japan/East Sea during the winter of 2009-2010 is evaluated through analysis of weekly, 10 km resolution AVHRR multi-channel sea surface temperature (SST) data provided by the Naval Oceanographic Office. Between October 2009 and January 2010, the average magnitude of the across-front SST gradient increases from 0.05°C/km to a maximum of 0.14°C/km. The maximum SST gradient observed at any point along the SPF, calculated by centered differencing across 10km grid cells, is 0.29°C/km during the week ending 28 January 2010. SSTs averaged across broad areas north and south of the front show a 12°C cooling south of the front and 17°C cooling north of the front between October 2009 and February 2010. The strength of the SPF remains fairly constant (average magnitudes of 0.11 - 0.14°C/km) between late December 2009 and early March 2010, with occasional strengthening in response to cold air outbreaks. The position of the SPF, defined by the location of the maximum SST gradient between 38°N and 41°N, generally aligns with bathymetric contours between 129°E and 131°E (along a ridge extending northeastward from the East Korea Bay), and between 135°E and 139°E (along the 3000m depth contour east of Yamato Rise).