Three-Dimensional Multiple-Radar Reflectivity Mosaics And It's Application Study

This paper describes a technique of gridding radar reflectivity observations under quality control from multiple radars and combining them into a unified 3D merged reflectivity grid with high resolution. Then, some preliminary studies on the application of 3D reflectivity grid are made. The 3D mosaic grid is a powerful tool of the deep and wide application of radar network data (e.g. severe weather warning and nowcasting, data assimilations for convective-scale numerical over large domains, the application in hydrology and aviation) . The main contents and conclusions are as follows:1 A reflectivity quality control (QC) algorithm has been developed for identifying and removing non-precipitation echoes from the radar base reflectivity fields. The algorithm assumed that precipitation and non-precipitation echoes had different horizontal and vertical reflectivity structures. Two main parameters, vertical gradient of reflectivity with height constraint and horizontal texture of reflectivity, and a set of physically based rules and criteria were developed for the QC algorithm. The reflectivity QC algorithm has been tested using some volume scans of base level data from different radar sites and from different atmosphere conditions. Results have shown that the reflectivity QC algorithm is very successful in identifying non-precipitation echoes.2 The beam occultation, which is the percent of the radar beam power lost due to beam blockage, was calculated using an algorithm that used high resolution DEM(digital elevation model) data, radar beam pattern (Gaussian beam approximation), and radar beam propagation path (assuming radar beams propagate under standard atmospheric refraction conditions). Hybrid elevation angles and hybrid scan reflectivity were generated using based on beam occultation. Comparison of model-calculated beam occultation with radar observations indicated very good qualitative agreement and strongly quantitative correlation. In order to know the coverage capability of weather radar network, the standard refractive index beam heights (4/3 earth) were calculated for hybrid elevation angles for every radar in radar network, which were combined to produce a mosaicked beam height map.3 Four interpolation approaches were investigated to remap raw radar reflectivity fields onto a 3D Cartesian grid with high resolution. Through comparison of vertical and horizontal reflectivity cross section and estimated one-hour precipitation obtained by use of the four interpolation schemes, it was found that the vertical interpolation scheme with nearest neighbor on the range-azimuth plane was the most reasonable analysis scheme that provided consecutive reflectivity fields and retains high-resolution structure comparable to the raw data. Comparing reflectivity observation with corresponding reflectivity analysis obtained respectively by interpolation using reflectivity factor in dBZ and in mm6/m3 , results have shown that on the whole, the analysis field obtained by interpolation using reflectivity factor in dBZ was more accordant with observation field.4 In order to check spatial coherence and calibration differences of three regional radar network when they detected synchronously atmosphere, horizontal and vertical structure of reflectivity fields on equidistant line from radar-pairs were analyzed. Results have shown Wuhan radar's echo intensities were weaker than that of adjacent radar, whereas, Yichang radar's were stronger. Echo's vertical structures are quite large variation on equidistant line when Changde radar simultaneously observes with around 3 radars, its echo height is obviously lower. Nevertheless, the others'echoes are consistent well.5 Four approaches of combining multiple-radar reflectivity fields were investigated. Results have shown the distance- exponential-weighted mean scheme provided a spatially consistent reflectivity mosaics while retaining the magnitude of the observations from the close radar. Mosaics could mitigate various problems that caused by the geometry of radar beam such as data voids with the cone of silence above the radar and in regions below the lowest beam.6 Based on 3D merged reflectivity grid, some radar network products used for warning effectively severe weather were developed, which were proved to be reasonable through Comparing radar network products with single radar product mosaics. The distribution characteristics of the six preparative reflectivity-morphological parameters from convective and stratiform rain were presented. Based on three of them, a fuzzy logic method for the partitioning of radar reflectivity into convective and stratiform rain classifications has been developed and tested using volume scan radar reflectivity data. Results have shown that the fuzzy logic method could separate reasonably stratiform and convective rain.