Analysis of the Spatial and Temporal Distribution Characteristics of the Cloud-Ground Lightning in Hubei Area

This paper revealed spatial and temporal distribution characteristics and rules of lightning activity in Hubei Area.The results can be used in lightning protection and lightning risk assessment.The research is based on the cloud-ground lightning data from Mar.2006 to Feb.2009 collected by the lightning detection and location system which is composed of 13 lightning detectors.The daily and monthly lightning variation,lightning intensity,polarity and density,and the time and space distribution features of cloudground lightning in Hubei area are analyzed.The results are showed as follows;the ratio of negative lightning is 96.2%,and the ratio of positive lightning is 3.8%;Daily variation of lightning frequency shows obviously single peak and single valley,its maximum value appears at 15:00—16:00 LT(local time),the minimum value appears at 9:00—10:00 LT.The number of the lightning appearing from April to August in one year accounts to 96.7%of the annual total;the lightning appears most frequently in July and August; The intensity of positive and negative lightning is mainly concentrated in 10—50 kA.The number of the lightning whose intensity more than 30 kA accounts to 50%of the total,more than 60 kA accounts to 8.1%,more than 100 kA accounts to 1.6%.A probability equation is set up according to the lightning intensity and its corresponding cumulative frequency.Through statistical analysis,the correlation coefficient between the measured values and the calculated is as high as 0.99998.Lightning density distribution has obvious regional difference,the high density areas of lightning are cities of Jiayu,Xianning,Huangshi, Ezhou in Southeast Hubei.And the second high-density areas are Yuanan,Dangyang nearby in western Hubei.Mountains and hills,plain transition zone,that is,the situation of the surface changed significantly zone is a lightning-prone area.Thunderstorm days in mountain counties and cities in Southwest Hubei are more,but lightning density does not necessarily increase as the thunderstorm days.The reason possibly is a result of the combined effect of two factors:the mountain county soil resistivity is larger and these places belong to the local microclimate environment.