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 atypi...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.展开更多
To quantitatively study the role of tropical cyclone precipitation(TCP) on alleviating the drought in the southeast coastal region of China(SCR) during summer and autumn,the objective synoptic analysis technique(OSAT)...To quantitatively study the role of tropical cyclone precipitation(TCP) on alleviating the drought in the southeast coastal region of China(SCR) during summer and autumn,the objective synoptic analysis technique(OSAT),improved for consistency and rationality,was used to separate the TCP data on the summers and autumns of 1963-2005 on the basis of daily precipitation data from stations and tropical cyclone best track data.After defining the season drought index,the actual drought distribution and the assumed drought distribution without TCP were acquired.The results showed that within 1 000 km from the southeast coastline of China,TCP accounted for 11.3%of natural precipitation(NP).Without TCP,the drought index in the SCR during summer would have increased from 0.2 to 0.6 or even above 1.0 in some regions whereas the drought index during autumn would have increased from 0.4 to 0.6 or above 1.2 in some regions.The impact of TCP on drought decreases progressively from the southeast coastline to the inland regions.The TCP proportion(TCPP) showed a significant negative correlation with the drought index in many regions of the southeast,and the significant region is wider in autumn than in summer.TCP relieved the drought most significantly within a range of 0-500 km from the southeast coastline.This drought relief showed different characteristics for the interannual variability in summer and autumn,and the cross wavelet transform indicated that the impact of TCP on drought mainly lies in 2-4-year time scales.In particular,there was a significant effect during the summers of 1977-1985 and in the autumns following that of 1985.Therefore,TCP has indeed largely alleviated drought in the SCR during summer and autumn.展开更多
基金supported by the National Research Fund for Public Welfare (Grant No.GYHY200906011)the National Key Technology R&D Program of China (Grant No.2009BAC51B01)the National Fundamental 973 Research Program of China (Grant No.2013CB430100)
文摘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.
基金National Fundamental Research 973 Program of China(2015CB452801,2013CB430100)
文摘To quantitatively study the role of tropical cyclone precipitation(TCP) on alleviating the drought in the southeast coastal region of China(SCR) during summer and autumn,the objective synoptic analysis technique(OSAT),improved for consistency and rationality,was used to separate the TCP data on the summers and autumns of 1963-2005 on the basis of daily precipitation data from stations and tropical cyclone best track data.After defining the season drought index,the actual drought distribution and the assumed drought distribution without TCP were acquired.The results showed that within 1 000 km from the southeast coastline of China,TCP accounted for 11.3%of natural precipitation(NP).Without TCP,the drought index in the SCR during summer would have increased from 0.2 to 0.6 or even above 1.0 in some regions whereas the drought index during autumn would have increased from 0.4 to 0.6 or above 1.2 in some regions.The impact of TCP on drought decreases progressively from the southeast coastline to the inland regions.The TCP proportion(TCPP) showed a significant negative correlation with the drought index in many regions of the southeast,and the significant region is wider in autumn than in summer.TCP relieved the drought most significantly within a range of 0-500 km from the southeast coastline.This drought relief showed different characteristics for the interannual variability in summer and autumn,and the cross wavelet transform indicated that the impact of TCP on drought mainly lies in 2-4-year time scales.In particular,there was a significant effect during the summers of 1977-1985 and in the autumns following that of 1985.Therefore,TCP has indeed largely alleviated drought in the SCR during summer and autumn.
