天津冬季一次雾过程分析

基于NCEP再分析资料及卫星遥感资料对2010年天津地区一次雾过程进行了研究,结果表明,500 hPa环流形势场上亚洲中高纬环流平直,地面处于低压场控制区,无强冷空气活动,有助于雾维持;雾维持阶段,天津及上游地区中低空有暖平流,呈下湿上干的湿度场分布;天津地区700 hPa以下为负垂直速度,对应正涡度及负散度,表明暖平流的侵入,使中低层存在弱的气流辐合上升运动;北京探空资料900 hPa以下的温度与露点温度廓线较接近,有逆温层存在,中高层廓线距离增大,低层风速偏小,有助于近地面层水汽凝结;卫星图像上雾区亮度稍暗,雾顶较光滑,纹理均匀,雾层在0.66μm处的反射率数值约为0.25,高于陆表及海面,雾区在11μm通道处的亮温为270～275 K,对于3.7μm通道的反射太阳辐射与0.66μm通道的反射率比值,雾区小于0.2,数值波动不明显。

Analysis of One Fog Event in Winter in Tianjin

Based on NCEP re-analysis data and satellite remote-sensing data,one fog event in winter of 2010 in Tianjin was analyzed.As known by the results,the 500 hPa circumfluence of Euro-Asia mid-high latitude area was flat,while the surface was low-pressure area,and there were no cold waves invaded.All these contributed to the fog continuance.During the period of fog continuance,there was warm advection in mid-low altitude in Tianjin and upriver area.The humidity field was wet in substrate and dry in superstratum.The vertical velocity was negative below 700 hPa in Tianjin area,while the vortex was positive and the divergence was negative.The convergence and raise movements appeared at middle and low altitude because of the intrusion of warm advection.The profile of temperature was close to dew point temperature profile below 900 hPa of sounding data,there was temperature inversion at that altitude.The distance between temperature profile and dew point temperature increased at mid-high altitude.The wind speed was small,which was propitious to water vapor coagulation around surface layer.The luminance of fog area was darker on satellite images,and the top of fog was glazed with uniform veins.In fog area,the reflectance of 0.66 channel was about 0.25,which was higher than that of land and sea surface.The brightness temperature of 11 channel was 270-275K,the ratio of reflected radiance of solar radiation in 3.7 channel to reflectance in 0.66 channel showed that the value was less than 0.2 in fog area,and the fluctuation of values was not obvious.