Gram-Charlier series distribution for ionospheric F2 layer characteristics

Analysis of foF2 and M(3000)F2 data for Washington, for the period January 1946 through July 1962, showed significant departures from normality of the monthly data distributions. The percentage of failures of the statistical test for normality was significant for all months of the year, but a striking seasonal variation in percentage of failures was noted, with peaks near the equinox periods, similar to the seasonal variations of geometric disturbance.