CINRAD-SA/SB零度层亮带识别方法

Bright Band Identification from CINRAD-SA/SB

该文提出一种使用S波段多普勒天气雷达回波三维特征和反射率因子垂直廓线(vertical profile of reflectivity,VPR)来自动识别零度层亮带的方法(简称3DVPR-BBID),并利用2003年6月22日—7月11日和2007年7月合肥雷达资料、2008年6月广州雷达资料以及相应的探空资料,同仅使用VPR识别零度层亮带的方法(简称VPR-BBID)进行比较。结果表明:VPR-BBID和3DVPR-BBID在大部分情况下能够有效识别零度层亮带的存在,而且3DVPR-BBID能够减少VPR-BBID产生的误识别。在同探空资料观测的零度层高度的比较中,两种方法确定的零度层高度同实况比较接近,进一步分析表明:3DVPR-BBID确定的零度层高度比VPR-BBID确定的更接近观测值。

The bright band caused by aggregated snow melting has increased the uncertainties in radar based quantitative precipitation estimation.However,the height of the bright band can indicate the 0℃isotherm and can be useful in identifying areas of potential icing for aviation and in the data assimilation for numerical weather predictions.Furthermore,the region of the bright band can also indicate the region of transition from convective to stratiform cloud which is useful for meso-scale weather analysis.Based on extensive analysis,an automated method to identify bright band with CINRAD-SA/SB Doppler radar based on vertical profile of reflectivity（VPR） and 3-dimension characteristics（horizontal,reflectivity gradient and vertical reflectivity lapse） of radar（3DVPR-BBID） is developed.The 3DVPR-BBID algorithm can determine from a volume scan-mean VPR and a background freezing level height from soundings if a bright band exists.To evaluate the performance of the 3DVPR-BBID,radar data from 22 June to 11 July 2003 and from 1 to 31 July 2007 in Hefei and from 1 to 30 June 2008 in Guangzhou are utilized,and a method which identifies bright band based only on VPR is also implemented for comparison.The results show that 3DVPR-BBID can identify the existence of bright band exactly and give the height of 0℃isotherm.The accuracy rate for VPR of bright band with 3DVPR-BBID is higher than that with VPR-BBID.The probabilities of identification between VPR-BBID and 3DVPR-BBID are 94.0%and 95.7%from 22 June to 11 July 2003 separately,85.4%and 92.3%in July 2007,81.0%and 89.8%in June 2008.The height of 0℃isotherm derived from 3DVPR-BBID and VPR-BBID are close to the sounding observation.Furthermore,the performance of 3DVPR-BBID is better than VPR-BBID.In most cases,the evaluation of 3DVPR-BBID is better than VPR-BBID based on mean absolute error（MAE） of different distance from radar.Since the time interval of soundings is longer,the algorithm can give higher time resolution data of the 0℃isotherm. When calculating the height of bright band with radar data,it＇s estimated that radar wave transmits with the standard atmosphere refraction.Another limitation is that VPR can only be used in certain parts of the radar detected regions.And there are some uncertainties with VPR in the distance far away from radar.