Abstract
In spite of many experimental and theoretical studies the relationships between storm dynamics, severe weather, and lightning activity have been least understood. Measurements of electric field made under a severe thunderstorm at a northeastern Indian station, Guwahati, India are reported. Lightning flash rate increases drastically to about 84 flashes per minute (fpm) during the active stage which lasted for about 7 minutes, from about 15 flashes per minute during the initial phase of thunderstorm. Sudden increase in lightning flash rate (‘lightning jump’) of about 65 fpm/min is also observed in the beginning of the active stage. The dissipating stage is marked by slow and steady decrease in lightning frequency. Despite very high flash rate during the active stage, no severe weather conditions are observed at the ground. It is proposed that the short duration of the active stage might be the reason for the non-observance of severe weather conditions at the ground. Analysis of Skew-t graph at Guwahati suggests that vertical distribution of Convective Available Potential Energy (CAPE) also may play some role in non-occurrence of severe weather at ground in spite of large lightning flash rate and lightning jump observed in this thunderstorm. Further, all electric field changes after a lightning discharge indicates the presence of strong Lower Positive Charge Centers (LPCC) in the active and dissipation stages. This suggests that LPCC plays an important role in initiation of lightning discharges in these stages.
Highlights
Measurements of electric field or lightning-induced electric field-changes at ground surface have been used for a long time to infer the in-cloud charge distribution and the changes in the distribution caused by lightning discharges (Standler and Winn 1979; Brook et al 1982; Krehbiel et al 1983; Maier and Krider 1986; Jacobson and Krider 1976; Livingston and Krider 1978; Pawar and Karma 2004)
The electrical characteristics of such severe Nor’westers have been studied for the first time using surface measurements of electric field and here we report our observations of electric field changes and recovery curves of lightning discharges made below an isolated thunderstorm at Guwahati (26.10◦N, 91.58◦E)
Even though no severe weather is observed at ground during this thunderstorm, the high flash rate and lightning jump certainly suggest that this thunderstorm had vigorous updraft in mixed phase region and large vertical depth
Summary
Measurements of electric field or lightning-induced electric field-changes at ground surface have been used for a long time to infer the in-cloud charge distribution and the changes in the distribution caused by lightning discharges (Standler and Winn 1979; Brook et al 1982; Krehbiel et al 1983; Maier and Krider 1986; Jacobson and Krider 1976; Livingston and Krider 1978; Pawar and Karma 2004). Williams et al (1999) have studied the behaviour of total lightning activity in severe Florida thunderstorms. Total lightning flash rate, 1–15 minutes prior to severe weather manifestation such as high surface wind, hail and tornado at the ground. Guha and De (2009) have studied the electrical characteristics of thunderstorms occurring in northwest region of India using sferics and they found some distinct peaks in the VLF range between 1.5 and 6 kHz. The electrical characteristics of such severe Nor’westers have been studied for the first time using surface measurements of electric field and here we report our observations of electric field changes and recovery curves of lightning discharges made below an isolated thunderstorm at Guwahati (26.10◦N, 91.58◦E). The evolution of lightning during different stages of the thunderstorm is discussed
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