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The cloud flash‐to‐ground flash ratio and other lightning occurrence characteristics in Kathmandu thunderstorms

 

作者: K. N. Baral,   D. Mackerras,  

 

期刊: Journal of Geophysical Research: Atmospheres  (WILEY Available online 1992)
卷期: Volume 97, issue D1  

页码: 931-938

 

ISSN:0148-0227

 

年代: 1992

 

DOI:10.1029/91JD02039

 

数据来源: WILEY

 

摘要:

Lightning and thunderstorm observations have been made in Kathmandu, Nepal (27.4°N, 85.2°E) over the 21‐month period March 1987 to November 1988 inclusive, using direct observations of thunder and lightning, and the registrations of a CGR3 lightning flash counter that provided records of the approximate numbers of cloud flashes, positive ground flashes, and negative ground flashes with an effective range of about 14 km. The observation period effectively covered two thunderstorm seasons as almost no lightning occurred during the winter months. During 1987 and 1988 the mean thunderdays per year was 42. The principal use of the CGR3 registrations was to estimate the long‐term ratio of cloud flashes to ground flashes, denotedz; it was found thatzwas 2.1 in 1987 and 3.0 in 1988, with a two‐season mean of 2.7. The uncertainty in ratio values is about 30%. The registrations also enabled lightning flash densities to be estimated with an uncertainty of about 40%. The two‐season mean ground flash, cloud flash, and total flash densities were 2.4, 6.6, and 9.0 km−2yr−1, respectively. There were well‐marked seasonal variations in occurrence, with about 82% of all lightning occurring between mid‐February and the end of May. During this premonsoon period there were steady rises to maximum values in May of the thunderdays per month (to 10), the monthly total flash density (to 2.9 km−2month−1), and the monthly value ofz(to 3.6). The range of values ofzcalculated from the records for individual thunderstorm days was 0.17 to infinity, but very little lightning was associated with the extreme values. A distribution of values of the ratio with respect to cumulative lightning occurrence shows that 80% of all lightning was associated with values ofz(calculated on a thunderstorm day basis) between 1.3 and 6.7. There is reasonably good agreement between the value ofzfor Kathmandu and values ofzfor other places at similar latitudes. However, major differences have been found for low latitudes between recently measured values ofzand earlier predictions of the lati

 

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