ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
A case study on the enhancement mechanism of squall lines moving into the Bohai Bay
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Abstract:
Based on conventional observation data, Doppler weather radar data and ERA5 reanalysis data, the physical process responsible for the enhancement and maintenance of a strong squall line affecting the Bohai Sea area during the night of July 31, 2021 was analyzed. The results show that coastal terrain and sea surface temperature were key factors affecting the intensity of squall lines. The warm water areas in the central and western Bohai Sea exhibited favorable conditions for thermal instability, and the areas with high wind speeds corresponded to the areas with high sea surface temperatures. The horn-shaped coastal terrain around the Bohai Bay exhibited the "narrow tube effect", resulting in significant wind field convergence on the windward side of the coast, which was conducive to the triggering of convection. In the early stage, the cold pool outflow formed by multi-cell storms on land converged with environmental airflow, causing the storms to propagate eastward and move into the sea. The non-uniform onshore winds caused by the complex coastal terrain of the Bohai Bay were conducive to the formation of new coastal thunderstorms. These thunderstorms merged and strengthened, ultimately evolving into squall lines. The mesoscale vortices formed by the cold pool outflow of squall lines and the environmental airflow along the northern coast of Bohai Bay promoted the propagation and strengthening of squall lines along the coastline. The development of coastal convection led to the spread of cold density towards the sea, which strengthened the intensity of the sea surface cold pool and was conducive to the development of offshore squall lines. In the process of strengthening squall lines over the sea, boundary layer frontogenesis played a crucial role. Compared with the cold pool effect, the influence of boundary layer temperature and environmental airflow was more significant, ultimately leading to the development and strengthening of squall lines in the warm water area of the Bohai Sea and their weakening and dissipation in the cold water area.
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