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

Abstract

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, denoted z; it was found that z was 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−2 yr−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−2 month−1), and the monthly value of z (to 3.6). The range of values of z calculated 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 of z (calculated on a thunderstorm day basis) between 1.3 and 6.7. There is reasonably good agreement between the value of z for Kathmandu and values of z for other places at similar latitudes. However, major differences have been found for low latitudes between recently measured values of z and earlier predictions of the latitudinal variation of z.

A Numerical Study of the Effects of Aerosol on Electrification and Lightning Discharges in Thunderstorms

“…7a and 7b that: (1) The first flash occurring in both types of thunderstorms is intra-cloud lightning (IC). The CG occurred later than the IC, and the frequency of the IC was higher than the CG, which is similar to the observation results (Mackerras, 1985;Baral and Mackerras, 1992). (2) The first flash of the clean thunderstorm occurs in 15th minutes, and most flashes occur in 15th minutes to 40th minutes.…”

Positive cloud‐to‐ground lightning discharges in Kathmandu thunderstorms

“…We have also attempted to find whether the proportion was related to ground flash or total flash activity on a daily basis. The instrument used to detect the different types of lightning is denoted CGR3 and has been described by Mackerras [1985], Mackerras and Darveniza [1986, 1992] and Baral and Mackerras [1992]. The method used to detect positive ground flashes is described in detail below, as the accuracy of the results obtained depends on the appropriateness of the method.…”

Lightning phenomenology in the Tel Aviv area from 1989 to 1996

“…The capabilities of the CGR3 have been described by Mackerras [1985] and Mackerras and Darveniza [1992]. The results of the survey were reported by Mackerras andDarveniza [1992, 1994], and reports for specific locations were given for Tel-Aviv [Fair and Levin, 1994], Katmandu, Nepal [Baral and Mackerras, 1992], and Gaborone, Botswana [dayarante and Ramachandran, 1996].…”