增强副热带高压对西南涡影响的数值试验

Simulation of Effect of Subtropical High Enhancement on Southwest Vortex

本文通过对伴随副热带高压(简称“副高”)东退而东移的一次典型西南涡天气过程(简称“20150721”过程)进行数值模拟,采用数值敏感性对比试验探讨了增大副高强度对这次东移西南涡的影响,得到以下结论:(1)副高强度增大以后,可长时间稳定维持,能对西南涡中尺度天气系统整个发展演变过程造成持续影响。西南涡路径和强度的变化直接改变了降水的落区和强度。(2)副高强度增大率先改变了环流场,使入侵的北风偏弱,西南引导气流偏强,最终导致西南涡发展偏弱、移速偏快。(3)环流场的改变直接影响到水汽输送、辐合辐散,从而进一步影响西南涡的发展演变过程。(4)副高强度增大以后,西南涡移速过快,导致了低涡中心与低层热力中心偏离,使得动力和热力中心不完全匹配,由此削弱西南涡发展强度。

Based on regional model simulations of a typical case of an eastward-moving Southwest vortex with the eastern retreat of a subtropical high(case 20150721),this paper discusses the effect of the strength of the subtropical high on the eastward Southwest vortex based on a numerical sensitivity test of a subtropical high enhancement.The main results are as follows:(1)An enhanced subtropical high can be stably maintained for a long time and can have a lasting impact on the development and evolution of the entire Southwest vortex meso-scale system.The area and intensity of precipitation directly depends on the path and intensity of the Southwest vortex.(2)The circulation field first changes when the strength of the subtropical high increases,the invading north wind becomes weaker,and the southwest guided airflow becomes stronger,which eventually results in a faster and weaker Southwest vortex.(3)The change in the circulation field directly affects the transport,convergence,and divergence of the water vapor,and further affects the whole evolutionary process of the Southwest vortex.(4)After the increase in the subtropical high,the faster Southwest vortex results in the deviation between the center of the Southeast vortex and the thermal center in the lower layer,which causes a mismatch between the dynamic and thermal centers and a weakening of the strength of the Southwest vortex.