Analysis on Triggered Mechanism of a Hail Weather in Tianjin

[ Objective] The research aimed to analyze triggered mechanism of a hail weather in Tianjin on July 10,2011. [Method] Using Micaps data, automatic meteorological observation data, sounding data and Doppler radar data, a hail process rarely happened in Daliutan Village, Yangli- uqing Town, Xiqing District, Tianjin City on July 10, 2011 was analyzed. Triggered mechanism of the hail weather was discussed. [ Result] The hail weather was generated by super cell which was triggered by sea breeze front and ground convergence interaction. Upper situation was in front of the forward tilted trough at bottom rear of the cold vortex, which was favorable for development of the strong convective weather. On ground map, water vapor transportation existed in easterly airflow at bottom rear of the high-pressure. Meanwhile, convergence zone also existed. It was wet lay- er over 0 ℃layer, and strong ascending motion existed, which was favorable for formation and development of the hail. Sea breeze front brought rich moisture, weak cold air and lifting effect when it moved toward inland from ocean, to make up for adverse conditions at low and middle layers. It could trigger a severely convective weather when moved to surface convergence zone. Doppler weather radar could monitor entire hail evolution process, [ Conclusion] The research had obvious guidance significance for judging hail process.

The Impact of Meteorological Factors on the Short-term Cumulative Effect of Air Particulate in Tianjin

In order to reveal the rapid increase mechanism of particulate concentration in short time,a notion of short-term cumulative effect of air particulate is defined as the significant increase of pollutant concentration in a short time under the condition of breeze,stable weather and constant emission caused by human being's activities. Subsequently,an index of short-term cumulative effect is established with air diffusive equation,and then the macro-scale meteorological situation and micro-scale factors of forming the short-term cumulative effect are discussed with the observation data. The macro-scale meteorological variables contain upper-level weather situations and surface weather situations. The micro-scale factors mainly include the boundary-layer height and boundary-layer stability. The analyses show that boundary-layer factors and weather variables have a significant influence on the short-term cumulative effect. The notion of short-term cumulative effect will play an important role in interpreting the severe pollution weather.

Atypical Occlusion Process Caused by the Merger of a Sea-breeze Front and Gust Front

An atypical occlusion process that occurred in North China on 14 July 2011 is studied based on both observations and a real-data Weather Research and Forecasting （WRF） model simulation. The results show that this atypical occlusion process was significantly different from the traditional, synoptic-scale occlusion process that occurs within extratropical cyclones. It was caused by the merger of two cold-type mesoscale fronts. One of the fronts developed from the gust front of convective storms, while the other was a sea-breeze front. As the two fronts moved towards each other, the warm air between them was squeezed and separated from the surface. An atypical occluded front was formed when the two fronts merged, with the warm air forced aloft. This kind of occlusion is termed a ＂merger＂ process, different from the well-known ＂catch-up＂ and ＂wrap-up＂ processes. Moreover, local convection was found to be enhanced during the merger process, with severe convective weather produced in the merger area.