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Positive cloud‐to‐ground flashes and wind shear in Tel‐Aviv thunderstorms

1996; American Geophysical Union; Volume: 23; Issue: 17 Linguagem: Inglês

10.1029/96gl00709

1944-8007

Zev Levin, Yoav Yair, Baruch Ziv,

Tree Root and Stability Studies

The occurrence of negative and positive ground flashes in Tel‐Aviv, Israel (32.05 N, 34.45 E) has been monitored through daily registrations of a CGR3‐SN5 lightning flash counter (Mackerras, 1985). Measurements were conducted from 1987 to 1995, with the most continuous data sets available for the period 1992–1995. The lightning data was augmented by radar measurements of the thunderclouds (starting from 1994) and by radiosonde data. It was found that the fraction R of positive lightning from the total ground flash count is highly variable, with a long‐term average of 0.25. It is shown that storms having a relatively large value of R coincide with strong vertical shear of the horizontal wind component. The dependence of R on the intensity of the wind shear S in the cloud layer between the 0°C and −25°C isotherms, may be expressed by: log R = aS ‐ b , where a=0.1504 and b=1.1471.