Study On The Effect Of Cold Wave Events On Air-sea Heat And Momentum Fluxes In The Yellow Sea

The article focuses on the study of the influence of cold wave events on air-sea heat and momentum fluxes in the Yellow Sea. With air and sea reanalysis data CFSR (Climate Forecast System Reanalysis) from 2009 to 2013, the temporal and spatial distribution characteristics of air sea elements and air-sea heat and momentum flux during the cold wave active period from November to March of next year are analyzed. The Central Meteorological Station MICAPS data statistics 2009-2013 Yellow Sea cold wave weather process in frequency, intensity and influence path, and it is statistically and analyzed that air-sea heat and momentum fluxes change significantly during the cold wave process. Finally by the FVCOM regional ocean model and FVCOM-SWAVE wave coupled model it is simulated that air sea elements and air-sea heat and momentum flux characteristics during the typical cold wave process in the Yellow Sea, and cold wave elements especially wind wave factors’ influence on air-sea heat and momentum flux transfer function is comparatively analyzed.First, the cold wave active period refer to November, December and next year January, February, March. In the cold wave active period, the air-sea momentum fluxes exchange will strong and negative heat fluxes is remarkable under influence of the sea surface wind, air-sea temperature difference and ocean circulation factors etc. Characteristics of air-sea heat and momentum flux are different in different months. Momentum flux exchange is most strongly in December and January, the maximum value can reach 0.14 N/m2 in the eastern region of the Yellow sea, and it weaken below 0.1 N/m2 in the spring March. Heat flux show strong loss of heat character in the winter January,the heat loss center is also located in the eastern region of the Yellow sea, the maximum value is -250 W/m2,the heat flux intensity reduced to-50 W/m2 in the spring.According to the statistics of cold wave invasion of the Yellow Sea, the highest frequency month of cold wave occurred are November and December, the lowest month is January. Cold wave into the Yellow Sea path can be divided into two categories, one kind is for North Road, its cold air is close to the source, it usually take the shortest path from the polar to influence the Bohai Sea and the Yellow Sea in China and have a great strength; another is the west route, the cold air source latitude is relatively low,but another cold air will join on the way of its forward to the east. It also can cause strong winds and cool weather in the East China area.Compared with annual monthly average, air-sea heat and momentum fluxes exchange becomes stronger significantly during the cold wave process, in the north path cold wave the momentum flux increase about 1-5times and heat flux increase 1-6 times, in the west path cold wave the momentum flux increase about 1-5times and heat flux increase 1-4times.We select typical north and west path cold wave to proceed numerical simulation. The simulation result shows that air-sea heat and momentum fluxes exchange has obvious difference, because of the different path and strength between two typical cold waves. In the north path cold wave, heat and momentum fluxes gradually increased from the north to the south following the path of cold air. Heat and momentum fluxes response is more intense in the north path cold wave process,due to the more strong cold air. The cold air of the west path cold wave is in the low latitude,cold air move from west to east,the corresponding sea surface heat and momentum fluxes is also gradually increased from west to east. The cold air strength is weaker than that of the north path cold wave,so heat and momentum fluxes response is also weaker. momentum flux is weaker about 1/4 than that in the north path cold wave and heat flux is weaker about 1/2.The impact of wind wave on air-sea heat and momentum flux is further investigated,by contract different numerical simulation results of FVCOM-SWAVE experiment with different wave conditions and FVCOM control experiment. The results show that when wind waves are included, air-sea heat and momentum fluxes exchange can be enhanced both in the north path cold wave and the west,and the result is closer to the real. When wind waves increased 1.5 times, the momentum flux maximum value increased by about 60%, heat flux increased 25-175 W/m2. When wind wave was weakened, air-sea heat and momentum fluxes exchange can be weakened too.When wind waves were reduced 0.5 times, the momentum flux maximum value was reduced by about 20%, and heat flux decreased about 20-60 W/m2.The impact of wind wave on air-sea heat and momentum flux in different Yellow Sea regions is different. The zonal mean of three critical latitudes shows that momentum flux increase about 12.5%-18%, heat flux increase about 5%-10% under the influence of wind wave in the north path cold wave,and in the west path momentum flux increase about 2.6%-3%, heat flux increase about 3%-16%.