利用锋生函数对2008年年初昆明准静止锋生消过程的诊断分析

Diagnostic Analysis of Frontogenesis and Frontolysis of Kunming Quasi-Stationary Front in Early 2008 Based on Frontogenesis Function

利用ERA-Interim 0.125°×0.125°高分辨率逐6小时再分析数据,选取昆明准静止锋2008年1～2月长时间维持过程诊断分析了锋生函数及其各分项在锋面生消过程中的作用与贡献,并结合2016年1月20～27日锋面增强西进过程和1979年1月14～20日锋面减弱东退过程进行了比较分析。结果表明:(1)非绝热加热项对锋面生消作用较小,但存在显著的日变化。在辐射作用下,非绝热加热项日间表现为锋消,夜间为锋生。(2)西移冷气团在被高原大地形抬升过程中存在局地地形迫使冷气团下沉的情况,并导致垂直运动倾斜项表现为锋生。由于地形固定不变,局地锋生形成次级锋生带。次级锋生带与昆明准静止锋的形成、维持和东西摆动有密切的联系。(3)辐合辐散项和水平形变项是锋生函数变化的主要贡献项,其中水平形变项中的切变变形作用以锋生为主,而伸缩变形项在纬向产生锋生,在经向产生锋消。

Based on frontogenesis function, the frontogenesis and frontolysis of Kunming quasi-stationary front (KQSF) in early 2008 is diagnosed using high resolution (0.125°×0.125°, 6-h interval) reanalysis data of ERA-Interim. The role and contribution of each component of the frontogenesis function is also analyzed. Typical processes analyzed long-term maintenance of the front from January to February of 2008, the strengthening and westward advance of the front from January 20 to 27 of 2016 and the weakening and eastward retreat of the front from January 14 to 20 of 1979. Results indicate that diabatic heating has little effect on the frontogenesis and frontolysis of KQSF, but it exhibits a significant diurnal change. Under the influence of radiation, frontogenesis phenomenon occurs in the daytime and frontolysis phenomenon occurs in the nighttime. During the westward movement of cold air mass, the topography on the plateau generally uplift the cold airmass. However, the air mass can also descend due to local terrain forcing, which leads to frontogenesis due to the effect of vertical motion tilt. Since the terrain remains unchanged, the local frontogenesis mentioned above produces a secondary frontogenesis belt, which is closed related to the KQSF activities, including its formation, maintenance and swing. Horizontal convergence-divergence term and horizontal deformation term make primary contributions to frontogenesis. The major effect of shear deformation in the horizontal deformation term mainly causes frontogenesis, while the effects of the expansion deformation term are opposite in meridional and zonal directions. Its zonal effect causes frontogenesis, and its meridional effect causes frontolysis.