The Three-Dimensional Structure of Coastal Front Producing Heavy Snow over the Shandong Peninsula

The heavy snow process over the Shandong peninsula during 11－15 December 2005 was simulated with the mesoscale numerical model MM5. Based on the successful simulation, the high-resolution simulation data were utilized to analyze the development and three-dimensional structure of the coastal front which was the most important mesoscale system for the producing of heavy snow during this process. The analysis showed that there was cyclonic shear between northerly winds and westerly winds in the horizontal structure. The airflow was convergent and updraft on the northwest side of the coastal front, and was divergent and downdraft on the southeast side. It was a convergence area below 900 hPa along the coastal front, and a strong divergence centre was just above the convergence centre, which led to the strong updraft. The strongest updraft occurred just at 900 hPa that was near the top of the coastal front and zero isolines of divergence. The coastal front zone existed below 900 hPa with updraft extending to 700 hPa. The water vapor was carried from the lower to higher troposphere by the strong updraft, and enhanced the local precipitation. The heavy precipitation zone was located on the coastal front and its cold side. Based on the above-mentioned results, the conceptual model of the coastal front was proposed. The sensible and latent heat fluxes from the ocean are the key factors for the formation of coastal front, especially, the sensible heat flux is more important to the coastal frontogenesis.