APPLICATION OF RADAR REFLECTIVITY TO INITIALIZATION OF CLOUD RESOLVING MESOSCALE MODEL PART Ⅰ: RETRIEVAL OF MICROPHYSICAL PARAMETERS AND VERTICAL VELOCITY

For non-hydrostatic cloud resolving models with a grid spacing less than 10 km, the incorporation of microphysical elements and the coherence of physical variables in the initial field of numerical weather prediction are very important, however it has remained a difficult problem in the cloud analysis field for a long time. It is known that warm cloud microphysical processes link the transform of hydrometeors with vertical motion and the radar echo intensity has close relation with hydrometeors. So, it is possible to acquire microphysical variables in clouds from radar echo under the condition that only acceptable precision losses are paid. Under the conditions of warm cloud microphysical processes and hypothesizing the cloud in a stationary state at a given time, the water vapor mixing ratio(qv), cloud water mixing ratio( qc) and vertical velocity(w) can be obtained through rain water mixing ratio( q r), after the qr has been retrieved from the radar reflectivity factor(Z) through the Z-qr relation. A retrieval technique has been developed in this paper following the above thinking clue, and to illustrate its performance several retrieval experiments were performed using the Doppler radar observations of Hefei NEXRAD, Anhui province at 02：00 BST 5 July 2003. After some preprocessings such as the simple quality control, coordinate conversion, interpolation, and spatial smooth of the raw radar volume scanning data, qr, qv，qc, and w etc were retrieved. Results show that the CAPPI image at the level of 4 km obtained using the coordinate transform method is just the same as the output using radar station's technology. The patterns of mixing ratios of water vapor, cloud water, and rain water, and vertical velocity retrieved from the radar reflectivity accord well with those of radar echo intensity, and reflect satisfactorily the three-dimensional spatial structure of hydrometeors and vertical motion in the convective cloud. Echo characteristics of heavy rain on the meiyu front is very obvious, and the prominent cumulus embeds in the relative weak but broad stratus. In the stronger echo area, the qr, is usually larger below 6 km, with the maximum value more than 3.0 g/kg at the altitude of 4 km; the ascending velocity is the largest at about 5 km, and its value usually greater than 5 m/s; the qc is larger above 5.0 km, with the maximum about 3.0 g/kg at the level of 5 km; and the terminal velocity of rain drops is vertically, relatively homogeneous, about severa l m/s, but with the maximum at about 5 km. Due to the assumption that the cloud is in stationary state, there will be some errors in the retrieved variables within the clouds which are rapidly growing or dying-out, and in such cases, more sophisticated radar data control technique will help to improve the retrieval results.