Zhu Min

ABSTRACT

1. A 3-D conceptual model including flow field and dynamic and thermodynamic structure of movable meso--scale rainstorm depressions on Jiang-Huai meiyu front is established and some evolution features of the depressions are also analysed, it's pointed out that there has similar structure between the meiyu depressions and MCCs, i.e., a ``column of cyclonic vorticity'' extending from low level to high level almost vertically existing in both of these two kinds of MCSs.
2. The influences of different kinds of physical factors including moist physical process, surface radiation budget process, surface sensible and latent heat fluxes and atmospheric radiation process etc. on the development of rainstorms are discussed and it shows moist physical process and surface radiation budget process are the most two important factors, but surface sensible and latent heat fluxes and atmospheric radiation process also could affect the intensity of rainstorm depressions and their accompanying rainfall. On the basis of this, the role of condensational latent heat release is studied emphatically and a conceptual model of mutual positive feedback mechanism between the growing of meso--scale cyclone on MeiYu front and its accompanying intensifying precipitation due to stable condensational heating is posed, i.e. condensational heating generates negative allobar, divergent wind kinetic energy promotes meso--scale cyclone growing, and simultaneously, updraft motion is also reinforced, precipitation continues intensifying. In addition, the observational fact of condensational latent heat release promoting the forming of high level baroclinically unstable wave is also verified.
3. A conceptual model depicting the lee wave of Dabie mountains which lays in Jiang-Huai area reinforcing the rainstorms is posed by combining the theoretical calculations and practical observation , i.e. during Jiang-Huai meiyu season, under certain circumstatnces, a kind of constant wave as computed by theoretical calculations could appear on the lee side of Dabie mountains, when migrating rainstorms move to a proper position (i.e. the updraft branch) of lee wave of Dabie mountains, the rainfall could be intensified. In a sense, this conceptual model could be used to explain a fact in climatic statistics, i.e. thunderstorms and rainstorms often happen on the lee side of Dabie mountains.
4. With respect to the frequently-occurring zone and some relative concentration regions within the zone of meso-scale systems, a new point of view is posed by case study. It's pointed out that the zone basically corresponds to meiyu front and its accompanying cloud and rain belt, or so-called warm and moisture tongue and LLJ etc. While the relative concentration regions match the rainfall centers on the meiyu front over the middle and lower Yangtse valley.
5. On the basis of the first-guess fields (interpolated from large-scale assimilated data) for hydrostatic PSU/NCAR MM4, relative humidity data with the same resolution as satellite pixel on mandatory levels retrieved directly from six basic factors, i.e. 4-chanael including VS, IR1, IR2 and WV satellite measurements and precipitation probability & intensity are first introduced in domestic research to revise the model's initial humidity fields to explore the application of non-conventional observation -- GMS images to Jiang-Huai meiyu precipitation forecast, it shows comparing with the results of scheme without using satellite retrieved data to revise the model's initial humidity fields, the former scheme could increase the threat scores of predicted rainfall amount greater than 10mm or 25mm and the correlation coefficients between 24-hour predicted rainfall field and the observational field, specifically, the prediction using satellite-retrieved data could produce rainbelt size, rainfall center position and rainfall intensity all closer to the reality. Further comparative study indicates the prediction using satellite-retrieved data could increase the correlation coefficients of precipitation fields in the first 6 hour of 24 hour forcast interval notably but such is not the case in the subsequent forcast interval (6-24 hour).
6. On the basis of the enhanced analysis fields (improve the first-guess on the mesoscale grid by objective analysis of surface and upper-air observations ) for non-hydrostatic PSU/NCAR MM5, the reflectivity factor volumn scanning data collected by conventional weather radar are early introduced in domestic research to revise the model's initial humidity fields to explore the application of non-conventional observation -- radar reflectivity data to Jiang-Huai meiyu precipitation forecast, it shows comparing with the results of scheme without using radar reflectivity data to revise the model's initial humidity fields, the former scheme not only could improve synoptic situation and precipitation forecast, but also could help predict some meso-scale weather phenomena. Further comparative study indicates a point that the periods of positive affection on the prediction are varying for different kinds of sounding data. So in order to keep the positive affection on the prediction, the renewal of data information without delay in operational forecast is an important principle which should be abided by in meso-scale NWP. Otherwise, the introductions of meso-scale information included in conventional observation and radar sounding data into initial fields for meso-scale numerical model could also ameliorate the spin-up problem.
7. By following the developments of internal and external meso-scale numerical models with better performances like IAP fine-mesh model, PSU/NCAR MM4 and MM5, numerical simulation, data assimilation experiment, numerical sensitivity test and forecast scores are all used to explore the way of adapting the available advanced forecast model to the prediction of Jiang-Huai meiyu rainstorms, it shows non-hydrostatic MM5 due to its reasonable designs of dynamic frame and parameterization schemes of main physical processes and its powerful simulation or prediction capacity for large-scale synoptic situations, meso--scale rainstorm depressions and their accompanying torrential rainfall during Chinese Jiang-Huai meiyu season could be used to be improved to meet the requirements of Jiang-Huai meiyu rainstorms' prediction, the objectives of improvement include reinforcing the model's description capacity of sophisticated land-atmosphere interactions over Tibetan Plateau and its neighboring regions and amending the calculations of clear air atmospheric long-wave radiation in model's atmospheric radiation scheme.