Influence of the interaction between different low‐ and mid‐level wind couplings and orography on the evolution of mesoscale convective systems in northwest China: A case study

Abstract

A mesoscale convective systems (MCSs) event occurring in Northwest China is investigated to discuss the influences of interaction between different low- and mid-level winds couplings and orography on the evolution of MCSs, using high-resolution reanalysis data. The formation of a low-level anticyclonic circulation related to the plateau high caused the sequential occurrence of reverse and perpendicular low- and mid-level winds couplings and the stagnation and expansion of a high humidity zone originating from the mountains. In the case of reverse low- and mid-level winds coupling, mid-level winds were constantly lifted by low-level winds ascending the mountains, resulting in strong updrafts and relevant inertia-gravity waves occurring continuously in the upstream direction of mid-level winds. The unstable stratification generated by the high humidity zone prevented the inertia-gravity waves from propagating into the updrafts, leading to the maintenance and connection of the updrafts. Meanwhile, a strong downdraft occurred and maintained on the leeward side of the updrafts due to the coupling of the inertia-gravity waves associated with the uplift of mid-level winds with the inertia-gravity wave triggered by low-level winds ascending the mountains. Consequently, MCSs developed as they propagated into the updrafts, and perished abruptly when they reached the leeward-side downdraft. In the case of perpendicular low- and mid-level winds coupling, a broad and strong low-level updraft band formed and stayed on the windward side of mountain ridge due to terrain-induced uplift. Significant mid-level updraft and associated inertia-gravity wave were triggered on the side of the low-level updraft band blown by mid-level winds. The unstable stratification generated by the high humidity zone hindered the propagation of gravity wave into the low-level updraft band, leading to the maintenance of strength and continuity of the low-level updraft band. Consequently, MCSs maintained during their entire propagation along the low-level updraft band. This article is protected by copyright. All rights reserved.