Brook1.html Brook, M., M. Nakano, P. Krehbiel, and T. Takeuti, The electrical structure of the Hokuriku winter thunderstorms, J. Geophys. Abstract Lightning charges, location, and currents have been determined for 12 flashes from four winter storms observed on the Hokuriku coast of Japan during December 1977 through January 1978.
Additional data is available from a total of eight winter storms.
A strong correlation exists between the fraction of positive ground strokes and the vertical wind shear in the cloud layer. The shear provides a horizontal displacement between the charges that helps to ensure that an initiating positive streamer will continue down to ground rather than into the negatively charged region that would normally be located directly below it.