| A Study and Experiment on Severe Rainfallwith Numerical Weather Forecast in NingxiaUsing Geostationary Meteorological Satellite Infrared DataIn order to improve the ability of torrent rainfall forecast in Ningxia, which locates in northwest of China with an arid climate, the relationship between geostationary meteorological satellite infrared data and summer hourly precipitation in Ningxia was analyzed, the geostationary meteorological satellite infrared data were applied to retrieve the relative humidity at medium and low layers of atmosphere. Two different methods to retrieve humidity were developed using optimal artificial neural network and non-linear regression after optimal fitting transmission. The retrieved humidity was put into meso-scale nonhydrostatic numerical weather forecast model MM5V3 after variation analysis, and a severe convection event was analyzed with the retrieved relative humidity. The precipitation forecast was improved quantitively, the forecasted severe convection area was consistent with the observation, and the spin up was reduced as much as 25%. The experiment shows the implement of retrieved humidity enhanced the ability of numerical model to forecast severe convection in Ningxia.(1) Using infrared data of Geostationary Meteorological Satellite, the gray scale and other kinds of element were calculated or derived after map projecting and geographic calibrating.(2) Analysis on the relationship of the element above and hourly precipitation in recent summers in Ningxia was conducted. The summer hourly precipitation in Ningxia, especially those of the heavy rainfall events, had obvious characteristics in the satellite-derived data. a). The satellite data scatter in a pretty large area. b). The scattering areas of the data above contracted for the heavy precipitation of more than 5mm/h. c). The maximum rainfall events in all prefectures in Ningixa occurred in the relative warm and stable clouds, d). Vapor level is much lower compared with those in the heavy rainfall events in south China affected by geographical location and topographic characteristics, e). It is hard to satisfy the conditions of cold air and vapor together for torrent rainfall, in particularly the transportation of vapor in low atmosphere, f). It is one of the main reasons for the arid climate in Ningxia. The vapor, or humidity condition is the key to rainfall in Ningxia, especially to heavy rainfall event.( 3 ) Two kinds of non-linear models to retrieve the relative humidity with geostationary meteorological satellite infrared data were developed. 1.Optimal artificial neural network was set up for the relationship between infrared data of Geostationary Meteorological Satellite and relative humidity in the medium and low layers in atmosphere by error back propagation network training after the experiments with different nodes in each of two hidden layers. 2.non-linear regression wasconducted after optimal fitting to retrieve the relative humidity, a). Experiment showed that the network with 6 nodes in each hidden layer has the best-forecast ability. The BP network was developed by training, b). Successive regression on relative humidity and infrared data of Geostationary Meteorological Satellite was made with Non-linear transitions after optimal fittings taken from 48 functions. To avoid the over-fitting phenomenon, the stable and best-fitted models were adopted, c). The quality of retrieved relative humidity with infrared data of Geostationary Meteorological Satellite was greatly improved compared with the traditional method such as linear regression, d). The humidity at each layer in the low atmosphere in the stations of Ningxia can be retrieved with pretty high accuracy using the non-linear models above.(4) Variation and quality control: a). The retrieved relative humidity at different stations was expanded into the grids with variational method to match the meso-scale numerical weather forecast model MM5v3 for heavy rain forecast, b). The satellite data were quality controlled before re...
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