Analysis On The Relation Of Two Sea Fog Events And The Stratus Over The Yellow And East China Sea In Spring

Two sea fog events over the Yellow Sea and their relations with the stratus overthe East China Sea are investigated using observations and numerical models.Observations show that there are close relations between stratus over the East Sea andsea fog over the Yellow Sea. The distributions of northern anticyclone and southerncyclone, the rapidly replacement of cyclone by anticyclone force the stratus loweringto sea fog. The weather systems including their horizontal and vertical positions,strengths and movements play a major role in the formation of stratus-fog system;The positions of the synoptic high and low pressure systems are beneficial for thetransport of moisture; The subsidence over the Yellow Sea leads marine atmosphericboundary layer (MABL) to be stable, The lowering height of the MABL from south tonorth is helpful for confining the northward water vapor in the low level; Theinversion, dry layer generated by the subsidence and the colder sea surface have theobvious function in the formation and development of the sea fog; Results from themodels testify the transition of sea fog and stratus, effect of the inversion controlledby large-scale weather system, sea surface temperature, subsidence. The stratuschanges into the sea fog through horizontal and downward advection, if the cloudliquid water evaporates in the cloud, the relation of sea fog and stratus is southwardstratus and northward fog, but not joint each other. The evaporation induced by thesubsidence and condensation of the water vapor from the stratus over the cold seasurface make a key contribution to the northerly development of the sea fog.The observations of expeditions aboard affirm the stratus lowering to sea fog andthe fog lifting to the stratus. The strong inversion and dry layer above the fog top, theabsolute stability inside the fog, colder sea surface play important part in theformation and the development of the sea fog, turbulence leads to the dissipation. Thesea fog lifting to the stratus is one of the sea fog dissipation’s mechanisms, warmingin lower layer, speeding in the wind, the uplifting inversion triggered by instability generate the sea fog into stratus. The sea fog has the same structures with thestratocumulus, the ratio wavelength is about2km; The mean total concentration ofparticles is0.873个/cm~3, the mean liquid water content (LWC) is15.46g/m~3, dropletsize distributions concentrate on2-4um, the mean effective diameter is2.675um, theLWC increases with the sea fog thickening, and the droplet size distributions broadengradually.