A bipole pattern has been observed in the locations of lightning flashes that lower positive and negative charge to earth in mesoscale storms systems. The pattern has a characteristic size of about 100 km and may last for many hours. The pattern is aligned with the upper level winds and has been observed in all seasons, but is more apparent in the fall and winter. The ratio of the positive flash density to the negative flash density is approximately 0.1, but varies from 0.05 to 0.2. This ratio occurs because there are fewer positive flashes and they are more spatially dispersed than negative flashes in storm systems. ¿ American Geophysical Union 1988