Numerical simulation of a sea fog process in the Oyashio Extension area

ZHANG Xin; ZHANG Suping

doi:10.13984/j.cnki.cn37-1141.2025.04.001

Abstract：The mid-latitude northwest Pacific Ocean is the high incidence area of sea fog,and it is also the way for China to reach the Arctic sea.However,due to the few observations at sea,the under-standing of the formation mechanism of sea fog is limited.From September 12 to 14,2019,the re-search ship"Xiangyanghong 1"recorded a sea fog event in the Oyashio extension area.In this paper,the formation mechanism of the sea fog was studied mainly by numerical simulation,numerical experi-ment and observations from scientific research ships.The results showed that:(1)The sea fog oc-curred in the warm area of the extratropical cyclone,and the warm front of the synoptic scale advanced to the north,forming a large range of front inversion over the cold water of the Oyashio extension pro-viding favorable weather background conditions for the development of the clouds/fog.(2)The atmos-pheric boundary layer above the cold water side of the ocean front(sea surface temperature front)was a"double inversion"structure.The superposition of subsiding inversions and frontal inversions caused by the subsiding branch of the local low-level secondary circulation forced by ocean front was an impor-tant reason for the formation of the"double inversion".The numerical results showed that with the smoothed ocean front,the strength of the sinking branch of the secondary circulation in the boundary layer was weakened,the scope of the"double inversion"structure disappeared,and the scope of the fog area was significantly reduced.(3)Both temperature and humidity in the fog rose,but the actual water vapor pressure rose faster than saturated water vapor pressure,the humidification effect was greater than the warming effect,which was obviously different from the cooling and humidification dominance of sea fog in spring and in summer in the Yellow Sea.This study revealed one of the reasons why sea fog tends to occur on the cold side of the ocean front in the open ocean,which can provide a new theo-retical support for sea fog forecast.