Application Of Doppler Weather Radar Non-precipitation Echo To Nowcasting

Non-precipitation echos were few Researched with restrict to detectivetechnique and data, because it is too weak to be detected by traditional radar. Withdeveloping of detective technique and increasing of data, more and moreNon-precipitation echoes are detected and studied as result of powerful and sensitiveNEXRAD in recent years. Product of Doppler velocity is becoming a important toolof nowcasting. Advances in researches and operational applications ofNon-precipitation echoes are briefly reviewed.By factual observation, echoes are often appeared in the 30-50km ranges aroundthe radar station which reflectivity is less than 20dBZ,and there is no precipitationaffair happening near the station. Non-precipitation we called. Inversion layer or theturbulence near the surface or the cloud above the station may cause this kind ofecho. Non-precipitation echo is easily detected by high sensitive Doppler radar andthe characteristic of Doppler velocity reflects the structure of the wind fieldaround the station.On basis of new generation single Doppler radar data collected recent years inTaiyuan, the genesis and pre-development characters of no rainfall echo are analyzedin different weather scale system, the observation results suggest that Doppler radialvelocity fields are quite similar between no rainfall echo and large area precipitationinside 30-50 km range. It leads obvious difference of zero velocity line in two side ofradar station account for combination of cold (warm) advection and convergence ordivergence. The negative velocity area is larger than positive while advection lapswith convergence, and the difference of azimuth forward positive is little than 180° between two zero speed line in equal distance, by comrades, advection hybrids withdivergence conduces that negative area is less than positive and azimuth differencebigger than 180°. All of these characters very agree with Doppler radar velocitypicture of large scale precipitation.The research job in non-precipitation echo is another significative try fornowcasting work. There is a well correlation between the characteristic of velocityecho figure and the formation, development and dissipation of rain system. Thestatistic study by two years data shows that there is a 5-7 hours forcasting time aheadof rainfall course. The results indicate that the non-precipitation echo's characteristicof velocity figure has a higher precision in forecasting ratio and is a new effectiveway for nowcasting.