张苏平,任兆鹏. 2010. 下垫面热力作用对黄海春季海雾的影响——观测与数值试验[J]. 气象学报, 68(4):439-449, doi:10.11676/qxxb2010.043
下垫面热力作用对黄海春季海雾的影响——观测与数值试验
The influence of the thermal effect of underlaying surface on the spring sea fog over the Yellow Sea: Observations and numerical simulations.
投稿时间:2008-12-29  修订日期:2009-04-29
DOI:10.11676/qxxb2010.043
中文关键词:  黄海海雾,海表面热状况,数值试验,MABL,稳定度
英文关键词:Yellow Sea fog, Sea surface thermal condition, Numerical experiment, MABL, Stabi lity
基金项目:国家863项目(2006AA09Z149),中国气象局行业专项(GYHY200706031),国家自然 科学基金项目(40975003)
作者单位
张苏平 中国海洋大学,物理海洋实验室和海洋 大气相互作用与气候实验室青岛266100 
任兆鹏 中国海洋大学,物理海洋实验室和海洋 大气相互作用与气候实验室青岛266100
青岛市平度市气象局青岛266700 
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中文摘要:
      利用海上浮标站、高分辨率数字式探空仪等多种观测手段和中尺度模式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,气温明显下降,气海温差(海表面以上2 m气温减海表面以下1 m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。较强的湍流活动出现在大气边界层低层150 m以下。反映了低层大气稳定性减弱,可能有利于海雾的维持。海雾消散阶段,海气温差明显加大,湍流强度减弱,湍流发展高度升高。海雾过程中,可能存在动量下传的局地海-气相互作用机制,SST的升高可使雾中能见度好转。数值模拟的结果与观测基本一致,雾区内的气海温差明显小于雾区外,敏感性试验进一步表明:100 m以下气层稳定性和湍流发展条件对SST的变化敏感。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 )的薄海雾区,SST增加1℃,稳定度明显减弱( ),海雾面积缩小;SST下降1℃,稳定度增加( ),薄海雾面积增大。在湿度较大( )的浓海雾区,SST的变化对静力稳定度的影响不大,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。
英文摘要:
      A sea fog event occurred over the Yellow Sea on 2-3 May, 2008 is investigated in this paper through various observational data and a three dimensional mesoscale model WRF. The satellite images depict the fog area of almost sea basin scale at its peak phase, and the fog is a typical cooling advection one that often occurs in the Yellow Sea fog season (from April to July when sea surface is cooler than air temperature) according to the synoptic conditions and sea surface tempertures.The buoy observations near Qingdao show that the surface air temperature (SAT, 2 m above sea level) decreases obviously when fog starts to occur with visibility dropping sharply below 1000 m and that the differences between the SAT and the sea surface temperature (SST, 1 m under water) reduce to less than 0.5℃ during the sea fog maintaining. The SAT is even lower than the SST in dense fog with the lowest visibility. The digital soundings indicate that stronger turbulence occurs below 150 m in the lower levels of the marine atmospheric boundary layer (MABL) during fog, reflecting that weaker stability is possibly in favor of sea fog generation. The differences between the SAT and the SST become greater distinctly and the turbulence is weakened in the intensity with its developing levels rising in the dissipation phase of fog. The local air sea interaction mechanism of momentum transport downward could play a role in the fog process, with higher wind speed as the result responding to warmer SST that is one of the conditions favoring better visibility.The numerical simulations with the WRF reproduce the variations of fog area and the horizontal visibility with time, which are consistent with the observations by satellite and from buoy. The difference between the SAT and the SST is less in fog areas than that out of fog areas. The effect of sea surface thermal condition on the sea fog is investigated quantitatively through sensitive experiments. The results show that the stability and turbulence under 100 m altitude are sensitive to the variations in the SST. The degree of the sensitivity depends on the water vapor content in the lower levels of the MABL. Under the conditions of lower humidity ( ) in the thin fog area, the stability can decrease (increase) obviously ( ( )) and the thin sea fog patch shrinks (enlarges) evidently with the SST rising (dropping) 1℃; while in the dense fog patch with a higher humidity ( ), the effect of changing in SST on the stability is not so obviouse, and the dense sea fog can be maintained. Therefore, if the difference of SST and SAT is small, even SST is higher than SAT, 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.
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