高纬度强对流与对流层上层水汽变化关系的数值模拟研究

应用WRF中尺度模式模拟了发生在黑龙江省西南部的一次区域性暴雨过程,通过云微物理参数化方案的敏感性试验,分析了对流云体中水汽垂直输送特征.结果表明:强对流活动使对流层上层局地水汽平均增加10倍以上,对流活动对于水汽的垂直输送以及对高层水汽含量的改变具有非常显著的作用.云微物理参数化方案,对于整个对流层水汽通量密度变化趋势有较好的表现.在不同方案中,0.5 ～9 km水汽通量密度及24 h总水汽垂直输送量,随高度变化差异较大.这是由平均垂直速度对不同方案敏感性造成的,不同的参数化方案,水汽通量最大值间最多相差可达27.9％.在不同的方案中,对流层上层加湿作用持续时间和对流层上层平均水汽混合比的最大值较敏感:对流活动可造成模拟区域对流层上层增湿持续16 ～20 h不等;对流层上层平均水汽混合比的最大值差异明显,最大可达15.8％.进行24 h平均后,上述物理量对方案的敏感性可减小到8.3％.所以,云微物理方案的不确定性对于暴雨过程的时间尺度是不可忽视的.

A numerical simulation on the relation between water vapor content variation in upper troposphere and strong convection weather in high latitude areas

Weather Research Forecast (WRF) model is used for studies of dynamic causes and thermal mechanisms of the rainstorm in the southwest of Heilongjiang. The vertical transport of water vapor by a severe convective process has been investigated using the WRF model with different cloud micro-physical schemes. The major conclusions are as follows: severe convections make local vapor in upper troposphere increase over 10 times, which shows that severe convections have a significant effect on both the vapor vertical transportation and the vapor content change in the upper troposphere. When the convective cloud arises, the trend of the water vapor flux density over the whole troposphere is not sensitive to cloud microphysical schemes. The strength of water vapor flux and the total water vapor flux integrated over a period of 24 h are sensitive to cloud microphysical schemes, which is correlated to the vertical updraft in the cloud. The largest difference in the maximum total water vapor can reach 27.9% among different schemes. Both the humidifying effect in the upper troposphere and the duration are sensitive to cloud microphysical schemes. The cumulus transport leads to humidification of the upper troposphere, which lasts from 16 to 20 h. The maximum differences in the upper troposphere water vapor mixing ratio can reach 15.8%. The averaging of 24 h may reduce the sensitivity of upper troposphere humidity, but the maximum still can reach 8.3%. The uncertainty induced by different microphysical schemes cannot be neglected within time scale of the rainstorm.