A study of the morphology of ionospheric storms

A study was made of the variations of the maximum electron number density in the ionospheric F2 layer during magnetic storms. Fifty-one strong storms and 58 weak storms were studied. The data were collected during the ten-year period 1946–1955, at 38 ionospheric stations between 60.4°N and 60.4° geomagnetic latitudes. The ionospheric stations were put into eight zones according to their geomagnetic latitudes. Storm-time variations in the maximum electron number density (Dst) and disturbance daily variations during each six-hour period (DS) were obtained for each of the eight zones. The Dst variation in higher middle-latitudes was characterized by an initial short increase followed by a much larger decrease, the amplitude of the decrease being accentuated in summer. In the equatorial region, however, the phase of the variation was the opposite of that in higher latitudes. There was generally an increase after an initial short decrease, with no seasonal effect. The Dst variation at intermediate latitudes resembled that at higher latitudes in summer and that at the equatorial region in winter, with the average over all seasons being relatively flat. The diurnal component of the DS variation for each six-hour period indicated, on the harmonic dial, a change in the clockwise sense except in the equatorial region. The maximum amplitude of the diurnal component of the mean of the DS variations showed a gradual decrease from higher toward lower latitudes, with a subsequent increase in the equatorial region. A remarkable change of the phase of the diurnal component also occurred from higher toward lower latitudes.