Mesoscale characteristics analysis of "parallel" dual sea breeze fronts and associated convection initiation mechanism in the Shandong Peninsula

The sea breeze front is an important system that triggers convective weather in coastal areas, but few observations and research on the dual sea breeze fronts are reported. This article uses conventional observation data, Doppler radar, Himawari-9 satellite, and ERA5 reanalysis data on July 9, 2023, to analyze the mesoscale characteristics of two "parallel" sea breeze fronts moving towards each other that cause severe convective weather in the eastern part of the Shandong Peninsula. The mechanism that triggers strong convection is preliminarily explored. The results are as follows. (1) The dual sea breeze fronts that triggered this severe convective weather were located along the coast from Fushan to Mouping (northern sea breeze front) and from Haiyang to Rushan (southern sea breeze front). The surface environmental wind at the time of their appearance was the southwest wind. At the initial stage of the northern sea breeze front, it showed a northwest-southeast direction. But it gradually turned into a northeast-southwest direction as it advanced southward, which was parallel to the southern sea breeze front. (2) Peak gusts can assist radar in determining the location of the sea breeze front. When the dual sea breeze fronts passed through, there was a significant difference in the changes of surface meteorological elements between the northern and southern coasts. There was a clear north-south wind transition on the north coast and a significant increase in relative humidity on the south coast. (3) In the early stage of strong convection, there were low-level atmospheric disturbances and uplifts in the sea areas on both the northern and southern sides of the eastern Shandong Peninsula, which advanced inland. With the establishment of the dual sea breeze fronts, the low-level atmospheric disturbance uplift areas on both the northern and southern sides merged with the uplift areas of the dual sea breeze fronts. These two merged uplift areas continued to move towards each other until they merged into the strongest updrafts, which subsequently triggered short-term heavy rainfall and downburst severe convective weather.