Study For Water Cycle And Diabatic Heating Processes Of A Mesoscale Convective System In The Dabie Mountains Area

The statistics results show, the accuracy of 24-hour precipitation forecast in China is up to 83%; but the accuracy of heavy rainfall is only 19%, mainly due to the relationship between heavy rainfall ant meso-βscale weather systems, hard to be rapidly and accurately captured by conventional observation networks. Due to imprecise initial field and deficiency of model itself, the numerical model system can not give accurate forecast to heavy rainfall too. Therefore, carrying up effective mesoscale observations, getting plenty of three-dimensional meteorological data and amalgamating them are very important in studying of the structure and mechanism of heavy rain. Under favorable environmental conditions the strong water vapor convergence and upward motion will cause the development of cumulus convective clouds. Through water vapor convergence, rising and condensation to release a large amount of latent heat, the cumulus convection affects the large-scale environmental field, and feedback to the meso-scale system itself. The latent heat released and absorbed by the phase transition of water substances and drag action caused by precipitation have significant affect in the thermal and dynamic process of environment. Therefore, the study of heat, water vapor budgets, cloud microphysical process and the interaction between them and the environmental field are very important component parts in the study on the occurrence and development of meso-scale heavy rainfall.But few scholar links the-water cycle and the diabatic heating, to discuss the their relationship and affects to heavy rainfall forms. In this thesis, LAPS data comes from the southern China heavy rainfall experiment (SCHeREX). During SCHeREX, we obtained abundant high spatial and temporal resolution 3D reanalysis data range of 113-119.57°E,28.5-34.02°N, horizontal resolution 0.03°x0:03°, vertical resolution of 22 layers and time resolution of 1 hour:By using the LAPS reanalysis data, we analyze the contribution to pricipitation of each items in water vapor budget, the amount of water vapor income and water substances and the phase transition among them. By calculating the budgets of apparent heat source and apparent moisture sink we analyze the diabatic heating characteristics and the relationship between heat and moisture. This thesis proves the ability of LAPS to assimilate data and describe the meso-scale system, its high resolution reanalysis data can be used as basic data for meso-scale meteorological analysis. According to the above anaysis, we reveal the inherent relationship between the water cycle and heating processes and the heavy rainfall.The theoretical calculated precipitation generated by total water vapor budget is 2.42 mm/h, accounting for 77% of actual precipitation (3.16 mm/h), and the eyaporation from surface ground is also an important source of vapor.87% of the water vapor income is contributed by the horizontal convergence term. The horizontal convergence which is mostly caused by wind convergence mainly occurs in middle and lower level. The western and southern boundaries are the major inflow boundaries. The local change term accounts for 12% of the total water vapor income. The maxima of flux divergence in low level and local income of water vapor appear 5 and 1.5 hours before the strongest precipitation moment respectively. Horizontal convergence and local change of water vapor in early period supply a large amount of water vapor for the vertical transportation and convergence of water vapor in late period. In the whole gas column averaged, the changes of water vapor income appear 1.5 hours ahead of precipitation changes, showing that in severe convective cloud system, the average time from water vapor in all height of air column condensation to falling to ground surface is about 1.5 hours. Water vapor decreases 2.42mm water content, causing 0.228mm water content increase of cloud particles and 0.042mm water content increase of precipitation particles, and eventually contributes to 2.15mm ground surface precipitation. The maximum of snow content appears just at the s heaviest rainfall moment; precipitation decrease when cloud ice content decreases rapidly, showing the ice-phase particles have important roles in this precipitation process. The maxima of cloud water and cloud ice appear 4 and 2 hours before the heaviest rainfall moment respectively, having certain forecasting significance for precipitation.In plain areas, the heat release of vapor condensation plays a major role to heating field; in mountain regions, the effect of sensible heat and ice-phase substance latent heat are not negligible. There are two peaks on the vertical profile of Q2, corresponding to the large value centers of water vapor flux convergence. Strong water vapor convergence causes a large amount of water vapor assembles and condenses to release latent heat in low level, forming the Q2 peak under 0℃layer. In this layer, melting snow absorbs great amount of heat, so Q1 is significantly smaller than Q2 in low layer. The other Q2 peak is located at maximum layer of vertical velocity. Water vapor is rapidly uplifted and condenses to heating the atmosphere. Simultaneously, many ice crystals grow up, casing the decrease of water vapor and the increase of heat. The combined effect leads to Q1 is bigger than Q2 in high layer.The characteristics of heavy rainfall process different from weak rainfall are is as follows:(a) the water vapor convergence is significant bellow 550hPa layer. (b) Cloud ice concentration in the ice crystal layer above 250hPa and mixed layer between 550-250hPa is very high (c) Snow concentration between 550-300hPa layer is relatively high. (d) Liquid cloud water is rich below the 500hPa layer. (e) The apparent moisture is significant in low layer. (f) The heating is notable in mid and high layer, in system matured moment.According to study for the interaction process between the mesoscale vortex system and severe convective system, we find that, cyclonic and convergent vortex system develops gradually from the lower troposphere to the upper troposphere, strengthening vertical upward movement, increasing the amount of water vapor condensation and latent heat release, and uplifting the heating height. All of these are beneficial to the convergence of moisture air in low layer, and then firm the development of convective instability and the strengthening of cyclonic vortex. This positive feedback makes the precipitation process continues, until the height of heating is not conducive to the development of low-level circulation. Then the strong convective system moves away from cyclone system, and precipitation decreases gradually.