【作者】 张苏平； 任兆鹏；

【Author】 Zhang Suping,Ren Zhaopeng Physical Oceanography Lab.,Ocean-Atmosphere Interaction and Climate Lab.,Ocean University of China Qingdao 266100

【机构】 中国海洋大学,海洋-大气相互作用与气候实验室；

【摘要】 本文利用海上浮标站、海岛梯度风观测塔、高分辨率数字式探空仪等多种观测手段和三维中尺度模式WRF,对2008年5月2-3日黄海发生的一次海雾过程进行了观测分析和数值模拟。观测表明,出现海雾时,海气温差(海表面以上2m气温减海表面以下1m水温)减小,不足0.5℃,浓雾时,甚至出现海温(SST)高于气温的现象。SST的升高可能使雾中能见度好转,而风速-蒸发-SST机制可能对SST的波动有贡献。数值模式的控制试验较好地反映了雾区范围的变化。敏感试验进一步定量研究了下垫面热力状况和湍流条件对海雾的影响,结果表明:100m以下气层稳定性对SST的变化敏感,浓海雾区的稳定度明显小于薄海雾区,表明较弱的稳定性可能有利于浓海雾的发展和维持。SST的变化对稳定度的影响和对雾区范围的影响与近海面的水汽含量有关:在湿度较小(q<0.5g/kg)的薄海雾区,SST增加,稳定度明显减弱(?θv/?z≤0.01K/m),海雾面积缩小;SST下降,稳定度增加(?θv/?z≥0.07K/m),薄海雾面积增大。在湿度较大(q>0.6g/kg)的浓海雾区,SST的变化对稳定度的影响不大,海雾仍然维持。因此,当海气温差减小,甚至出现SST高于气温时,如果仍然有海雾,则一般是水汽含量比较大的浓海雾。该结果有助于对海雾形成机制的认识。更多还原

【Abstract】 In this paper various observational data and a three-dimensional mesoscale model WRF are employed to investigate and simulate a sea fog event occurred over the Yellow Sea on 2 May,2008.The observations show that temperature differences between air and sea surface reduce to less than 0.5℃ during the sea fog formation. Sea surface temperature(SST) is even higher than the surface air temperature(SAT) in the case of dense fog. The mechanism of wind speed-evaporation-SST could play a role in the SST variations that may lead to the vibrations of visibility in fog. Numerical simulation shows that the variety of horizontal visibility with time iswell reproduced. The sensitivity experiments indicate that the stability under 100m altitude is sensitive to the variations in the SST,and that the less stable structure in the marine boundary layer(MABL) is found in the dense fog,which implies less stability is favorable to the development of dense fog. The degree of the underlying thermal effect on the stability as well as the sea fog areas depends on the water vapor content in the lower level of the MABL. Under the condition of lower humidity( q < 0.5g/kg) ,the stability decreases/increases obviously( θ v /z≤0.01K/m/θ v /z≥0.07K/m) and the thin sea fog area shrinks/enlarges with the SST rising/dropping 1℃;while in the dense fog area with the higher humidity( q > 0.6g/kg) ,the effect of changing in SST on the stability is rather weak,and the dense sea fog can be maintained. Therefore,if the difference of SST and AT is small,even the SST is higher than the AT,and if the sea fog still exists,the fog should be dense fog and the water vapor content is higher. This result is helpful to understanding of sea fog formation mechanism and forecasting.更多还原