一次大雾形成过程的数值模拟分析

利用非静力中尺度模式MM5V3对2009年11月30日到12月1日天津武清地区的一次大雾天气过程进行了数值模拟研究,这次大雾过程主要分布在天津、河北、山东地区,天津市武清县位于大雾的边缘位置.此次雾过程可以分为3个阶段.11月30日的17:00(北京时间,下同)至12月1日00:00是雾的形成阶段,12月1日00:00出现雾,00:00至09:00是雾的发展阶段,09:00之后是雾的消散阶段.模拟研究表明长波辐射降温使得温度下降并导致逆温层出现,同时由于暖湿气流输送,观测点处具有充足的水汽供应,促使了大雾的形成;在雾形成之后,逆温层的维持、持续的长波辐射降温有利于雾的不断发展;而后期辐散下沉运动明显,水汽不断向外辐散,使得雾逐渐消散.湍流对雾的影响是向上和向四周传输水汽,使得雾范围扩大,但如果太强,又会使得雾很快消散.

Numerical Study of a Dense Fog Event from 30 Nov to 1 Dec 2009

The NCAR/PSU MM5v3 model is used to simulate a fog event in the Wuqing area from 30 Nov to 1 Dec 2009. This severe fog was distributed mainly in Tianjin, Hebei, and Shandong; Wuqing was at the edge of the fog area. This fog event can be seen as having three phases: After the formation phase from 1700 LST 30 Nov to 0000 LST 1 Dec, fog began to form at 0000 LST 1 Dec. The development phase lasted from 0000 LST to 0900 LST; after 0900 LST the fog began to disperse. With a cooldown caused by long-wave radiation cooling, an inversion appeared; in addition, sufficient water vapor was transferred by a warm wet flow. Weak convergent upward motion occurred in the surface layer. Under these conditions, fog formed. The maintenance of the inversion and sustained long-wave radiation cooling is conducive to continuous fog development. In the third phase, fog began to dissipate as a result of vapor divergence. Turbulence transfers water vapor, but if the turbulence is too strong, fog will dissipate quickly.