Polar Ionospheric Disturbances Associated with a Severe Magnetic Storms

A detailed investigation is made of a severe magnetic storm on October 28th 1951, using world-wide simultaneous geomagnetic and ionospheric data. It has been found that an outstanding electrojet stream comparatively short-lived appeared near the southern edge of the auroral zone at the end of the main phase of this storm. The ionospheric disturbance associated with this electrojet was anomalous; the electron density of the F2 layer above the electrojet stream increased suddenly to more than 106 electrons per cm3 and then dropped below normal after the disappearance of the current stream. Although any existing theory of ionospheric storms can not explain satisfactorily this anomalous change, two possible mechanisms are suggested from some consideration of the direct association of geomagnetic and ionospheric variations. One is the effect of the incomming corpuscular precipitation into the ionosphere and consequently the formation of a new F2 layer due to the increase of ionization. The other is due to the vertical drift of electrons produced by the interaction of the geomagnetic field with the currents in the F2 region returning from the main electrojet formed in the E region.