A comparative study of two heavy rainfall processes in mesoscale simulation over Taihang Mountain Area

Heavy rainfall hit Taihang Mountain Area in north China on July 8-9, 2012. There were two main rainfall centers located in the south of the mountain and in Beijing area. Despite of the same occurrence time, these two precipitation processes were induced by different systems and distinguished from each other. This study compares these two rainfall processes and investigates different mechanisms that influence the convection initiation. Firstly, using a set of measurements and model analysis data, the synoptic and mesoscale conditions of the heavy rainfalls are diagnosed. The long-lasting heavy rainfall in the south of Taihang Mountain occurred with the development of large-scale synoptic circulation patterns. The combination of upper short wave trough, the middle and lower level shear line and the surface cold front together with the moist southeast flow provided favorable conditions for organized convection, producing wide range precipitation. In contrast, the system occurred in Beijing area was much smaller in scale and was hardly observed from satellite imagery. In fact, the short-time convection induced heavy local rains up to 50mm/h in Beijing area. Secondly, the operational forecasts by 3-km Weather Research and Forecast (WRF) model did not predict the small-scale system in Beijing area well. In order to study small-scale convection in Beijing area, high-resolution simulation is carried out using the Advanced Regional Prediction System (ARPS) driven by the NCEP GFS 0.5°×0.5°data. Finally, with the help of the fine simulation, convection initiation and evolution mechanisms for the two systems are further discussed. (a) Distribution of precipitation (mm) from 11UTC-23UTC July 8, 2012, overlaid with terrain height (m) and (b) FY-2E TBB (k) at 16UTC July 8, 2012