Analysis And Numerical Modeling Of Cold-air Outbreak Snowstorm Event In Shandong Peninsula

Cold-air outbreak snowstorm event has been the mainly disasters in winter in Shandong Peninsula, but people known this not very clearly because it occurred not frequently. So, the study is very necessary to improve cognition of this field.First, this paper used the precipitation data in Shandong Peninsula from 1980 to 2006 to analyse the synoptic circulation which arose the snowstorms. Results showed that snowstorms mainly occurred in December and the northern of Shandong Peninsula is the largest occurrence number places. The weather systems which caused snowstorms can be divided into two patterns: northeast cold vortex and trough line, and south trough line. The northeast cold vortex and trough line is predominant synoptic circulation of snowstorms in Shandong Peninsula.Then, this paper used reanalysed FNL data of NCEP to analyse the macroscale circulation in the Eurasia from 11-12 and 19-21, December 2005. These two snowstorm processes are similar, Shandong Peninsula are under the control of the northeast cold vortex at 500hPa and the trough line beyond the peninsula, the cold advection that after the trough is very clear. Under the influence of warm Bohai-sea surface, the cold airflow that from northwest was become warm and humid, which induces the accumulation of vapour and instability energy at lower layers. The upper and low-jet and the weak wind speed area stayed for a long time beyond Bohai-sea and Shandong Peninsula, these make the favorable synoptic circulation for the snowstorms.Using the simulated results of PSU/NCAR mesoscale model-MM5, combined with visible satellite cloud images from FY2-C and Doppler radar data, we analysed the mesoscale synoptic systems in these two snowstorm processes. Under the influences of the movement of northeast cold vortex, the updraft of secondary circulation generated by the coupling of upper and low-level jet. This secondary circulation make the instability energy to get together and the updraft aroused the release of instability energy in the lower layers, that makes the snowstorm in 21 December 2005 in the northern of Shandong Peninsula. The coast front plays important roles in the formation of mesoscale structure and the oscillation at peninsula coast of convective snowbands. The coast front is one reason of the increase of local snowfall. The results of numerical simulation of another snowfall indicated that the coupling of coastal front with gravity waves generated a less active gravity wave, which was named a wave trapped by coastal front. The especial geography position and landform of Wendeng county are the important reason of formation mechanism of snowstorm rookery.