利用WRF模式模拟青藏高原玉树地区一次层状云降水过程

Simulation of a Stratiform Cloud Precipitation Event in the Yushu Area of the Qinghai-Xizang Plateau Using the WRF Model

摘要: 利用中尺度数值模式WRF研究积云对流参数化方案和模式分辨率对青藏高原玉树地区夏季的一次层状云降水的影响。通过模拟结果分析表明：采用WRF模拟高原降水结果普遍偏大，三种积云参数化方案中GD方案模拟结果比较理想，不同方案对降水模拟比较敏感，相同方案下不同网格分辨率模拟降水分布基本相同。所用设计方案模拟的结果基本反映此次降水的实况和云图特征。在模拟实况温度和露点温度时，5 km分辨率的BMJ方案模拟效果相对于同分辨率其他两种方案明显更好。结合物理量场以及卫星云图分析本次层状云降水是由环流形势稳定、水汽充足、高原风切变共同影响。利用高分辨率的日本葵花8号卫星分析8 um和11 um红外通道分析云辐射亮温和水汽情况，降水时段玉树地区上空存在片状层云，并且水汽条件充足，环流背景场上玉树地区位于槽前，积云对流旺盛。此外，夜间露点温度差减小有利于形成较厚的云系导致高原夜间降水频繁。云图上发现，上升流场维持层状云团的发展和移动，高原夜间低层出现小而多的水汽云团，较小的云团混合生成较大的降水云系。

Abstract: The mesoscale numerical model WRF was used to study the effects of cumulus convection scheme and model resolution on the precipitation of stratiform clouds in Yushu over the Qinghai-Xizang Plateau in summer. Analysis of simulation results shows that WRF tends to overestimate precipitation over the plateau. Among the three cumulus parameterization schemes, the GD scheme yields relatively ideal simulation results, and different schemes exhibit sensitivity in precipitation simulation. Under the same scheme, different grid resolutions yield similar precipitation distributions. The simulated results using the designated schemes generally reflect the actual conditions and cloud features of this precipitation event. When simulating observed temperature and dew point temperature, the BMJ scheme at 5km resolution performs significantly better compared to the other two schemes at the same resolution. Combining physical field analysis and satellite cloud images, it is concluded that the stratiform cloud precipitation during this event is influenced by stable circulation patterns, abundant moisture, and wind shear over the plateau. High-resolution data from the Japanese Himawari-8 satellite’s 8um and 11um infrared channels reveal cloud radiative temperatures and moisture conditions. During the precipitation period, patchy stratiform clouds are present over the Yushu area with sufficient moisture, and the circulation background places Yushu ahead of a trough, promoting vigorous cumulus convection. Additionally, the reduced temperature-dew point temperature difference at night favors the formation of thick cloud systems, leading to frequent nighttime precipitation over the plateau. Analysis of cloud images indicates that the updraft field sustains the development and movement of stratiform cloud clusters, while small and numerous water vapor cloud clusters appear in the lower atmosphere at night, mixing to form larger precipitation cloud systems.