Research On Application Of Environment Parameters: CAPE Etc, To A Heavy Rain In Autumn In North China

During 9-12 ,October in 2003,there occurred an infrequent heavy rain and tempreture-falling weather process in Beijing,Tianjin,Hebei and Shandong.On the same time there experienced a storm tide in the Bay of Bohai.Using synoptic and dynamic methods, the circulation background and weather system on low-level and high-level of the heavy rain are analyzed. It is found that the center-deviated polar eddy the ridge of Mountain Ural high-pressure and the subtropical high-pressure are its macroscale influencial system .There are steady two-ridge and one-trough on high-level. The North China lies in front of the trough . The mesoscale cyclone ,the wind shear,the higher-pressure in north and lower-pressure in south are available circulation background for the event.The maintaining meeting of the warm humid air and cold dry air in the south of North China provides plenty of vapour for the heavy rain.In terms of the two-way nested grid mesoscale numerical model MM5(V3) is carried out for this heavy rain process. Based on the model products the θ_e field whin 10 to 11 is analyzed firstly. It indicates that the enough energy is accumulated on prophase and initial phase. During the rainstorm there is a strong ascending motion over the rainstorm area, which comes into being a strong updraft column. At the same time there are high-level atmosphere divergence and the low-level atmosphere convergence, it makes the strong ascending motion maintaining and advances the vertical transpotation of vapour , heat and energy .Secondly the environment parameters such as convective available potential energy (CAPE) storm relative helicity(SRH) and energy-helicity index(EHI) are calculated and analysed.The results show that the three parameters indicate the occurrence and development of the heavy rain. Much energy is accumulated before the heavy rain , so the atmosphere is very instable.After the severe convective weather breaking out the instable energy wears off, the value of CAPE falls to the minimum slowly. During the rainstorm the rainfall center lies in the isoline denseness area which is in the south of the low-layer helicity plus center. The axes of low-layer helicity plus center is concurrent with shear line and the convergence line of surface inversion trough. The high-layer helicity is related with high-layer jet. the severe storm take place under the condition of big-SRH and small- CAPE (SRH > 200 m2/s2,CAPE < 1500 J/Kg) . EHI reaches the max before the heavey rain happening.