Comparative analysis of valley topography effect on enhancement of two heavy rainstorms

Based on intensive automatic weather station observations in Hubei, conventional surface and upper data, 6-hourly reanalysis data form NCEP and FY-2E infrared satellite images, a comparative analysis is made on enhancement mechanism of valley topography to two heavy rainstorms events occurred respectively on 29 June and on 4 July 2012. The results show that both heavy rainstorms occur in advantageous circulation patterns and environment conditions and are affected by valley topography in Yangtze River Three Gorges. Confronting of cold and warm air and coordinating with resistance effect from valley topography force the horizontal and vertical flow fields near the ground changed, meanwhile, the interaction between the ground airflow flowing into gorges and the complicated topography leads to a local cyclone micro-circulation or convergence zone in the gorges. As a result the formation of topographic vortexes plays a crucial role to increase precipitation.The difference between the two events is that in the former event, cold air has more significant effect, more instable energy is accumulated and more complicated enhancement of valley topography exists including the narrow-tube effect, bell mouthed topographic effect and windward slope effect, so that this event has more efficient precipitation and higher rainfall intensity.