Day-of-the-week variability of hail in southwestern France

A study of the day-of-the-week variability of hailfall has been made using hailpad data, collected for 11 years in a large area of southwestern France. In the Atlantic region of this area, point hailfall frequency and intensity are not different on weekends and weekdays. In the inland region, the frequency is the same during both week periods, but the mean kinetic energy per hailfall is about twice as important on weekends as on weekdays. An analysis of the cot-responding mean hailstone size distributions for the two periods shows that both intercept and slope parameters of exponential size distributions, which fit with the observed ones are significantly different, and that the reduction in hail severity on weekdays is due to a shift from large to small hailstones. The day-of-the-week variability of air pollution measured in the inland region surrounding Toulouse suggests that anthropogenic emissions of ice-forming particles may be responsible for the observed hail change. (C) 2001 Elsevier Science B.V. All rights reserved.