| 摘要: |
| 首先介绍了闪电形成的概念模型,在此基础上提取反射率因子、环境等温层高度、最大反射率因子的对应垂直高度变化和垂直积分液态含水量来构建广东云地闪初生算法。其次,利用2007 年广东新一代雷达和闪电定位系统收集的大量强对流资料,对广东云地闪初生算法进行应用评估。对于138 个风暴样本,CSI 为69%,POD 为89%,FAR 为25%,空报较多。利用雷达垂直剖面资料分析误差产生的原因。算法漏报有两种情况:一是由于雷达天顶盲区的影响,使得该区域内的风暴垂直探测严重不足;二是环境等温层高度的估算存在困难,实际操作中选择了探空资料-15 ℃层的平均高度值。空报的主要原因在于一些风暴虽然达到或超过了反射率因子阈值,但是其强反射率因子核区在垂直方向上伸展不够,相对较薄,说明垂直运动不够充分,难以将水凝物输送到较高的环境等温层高度上,从而不会产生闪电。最后,根据误差分析对云地闪初生算法进行改进。一方面增加反射率垂直梯度因子的判别,减少因风暴垂直发展不足所造成的算法空报;另一方面,适当降低环境等温层的高度,选择7000 m 替代此前的7757 m。再次利用前面构建的强对流资料集,评估算法改进后的效果。改进后的算法在一定程度上控制了空报率,空报单体由此前的31个减少到23个,FAR 由25%降低至19%,但CSI则从69%增加到74%。 |
| 关键词: 云地闪 改进 检验 垂直梯度 |
| DOI：10.3969/j.issn.1004-4965.2011.06.008 |
| 分类号: |
| 基金项目:中国气象局新技术推广项目(CMATG2008Z11、CMATG2009YB09); 广东省科技项目(2011A030200014)共同资助 |
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| DESIGN OF AN ALGORITHM FOR INITIAL CLOUD-TO-GROUND LIGHTNING STRIKE |
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HU Sheng1, CAI An-an1, LIANG Jian-yin2, CHEN Zhi-gang1, HUANG Xiao-mei3
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1.Guangzhou Central Meteorological Observatory, Guangzhou 510080, China;2.Guangdong Meteorological Bureau, Guangzhou 510080, China;3.Zhanjiang Meteorological Bureau of Guangdong Province, Zhanjiang 524001, China
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| Abstract: |
| Firstly, an algorithm of predicting the first cloud-to-ground lightning strike in a developing convective storm is designed by combining the minimum reflectivity, the height of the -15℃ isotherm, the height of maximum reflectivity and vertically integrated liquid water. Secondly, this method for predicting cloud-to-ground lightning has been applied in 138 convective storms with an 89% POD, a 25% FAR, and a 69% CSI. The reasons to cause errors are discussed. Some storms are missed because of the limitations of radar shadow and estimation for the height of the -15℃ isotherm. More storms are false alarmed because most of them have weak updrafts, small soft hail, and thin strong-reflectivity core. No lightning occurs in those storms. Thirdly, a cloud-to-ground lightning algorithm is newly designed. The vertical gradient of reflectivity, defined as the decrease in reflectivity with increasing height in the 3-kilometer layer above the height of maximum reflectivity, is calculated to reduce false alarm. The height of the -15℃ isotherm is lowered from 7 757 to 7 000 meters. Finally, the lightning products are recalculated by using the improved method, which performs better than before. The CSI is increased from 69% to 74%. The number of false alarmed storms is reduced from 31 to 23. |
| Key words: lightning improvement verification vertical gradient |
