Identification and analysis of flash cells in thunderstorms

The convection-cell structure of a thunderstorm, often visible in the precipitation pattern of weather radar images, can also be identified in the clustering of ground flashes when their rate is high enough. The flashes can be grouped into cells with a set of rules applied to the time-ordered sequence of flash locations. A flash is associated with a group (cell) of older flashes if its distance and time lag are short enough, and some auxiliary conditions are fulfilled. With a careful choice of parameters the grouping algorithm, called Cellsearch, is able to resolve the flashes of a thunderstorm into a reasonable collection of ‘flash cells’ showing appropriate sizes, lifetimes and movements. The unavoidable occurrence of stray flashes, either true or caused by inaccurate locations, makes it necessary to reject some flashes from the cells and emphasize those in the cell core. All moderate-and high-activity thunderstorms in Finland during 1998–2002 are analysed for their flash-cell properties, and some representative cases are studied more closely. Copyright © 2005 Royal Meteorological Society

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