On Anomalous Variations of Maximum Electron Density and its Height in the F2 Region of the Ionosphere

Abstract

An explanation of anomalous variations of the maximum electron density (proportinal to (f0F2)2) and its height (hpF2) of the F2 region is attempted. For this purpose, the reexamination of the behaviours of f0F2, hpF2 and h′F2 in three seasons during sunspot maximum and minimum, is made and some interesting results are obtained. They are the followings. (i) The geomagnetic control of f0F2 is conspicuous in low and middle latitudes in there seasons. But above middle latitudes the geographic control is remarkable. This is applied above 30° in winter (greatest secχ) and equinox. (ii) f0F2 above 20° in December distributes approximately in such a way as f0F2∝cos1/2χ during sunspot minimum, but its distribution during sunspot maximum deviates from this line. (iii) The greater the zenith angle, the greater the increase of electron density from s. s. min. to s. s. max., and thus the magnitude of the seasonal anomaly of f0F2 is amplified far more during sunspot maximum than the minimum (iv) The value of hpF2 is greatest at geomagnetic equator throughout the year. (v) hpF2 becomes larger during sunspot maximum than the minimum. (vi) hpF2 in December does not increase at higher latitudes and rather decreases.From these facts it seems that the variations of f0F2 and hpF2 are controlled not only by the geomagnetic cause, but also by the cause which relates to the geographic latitude or solar activity. We investingate the geomagnetic distortion of daily variation of electron density due to the vertical electron drift, taking the diurnal and semi-durnal components into consideration, and show that the trough in geomagnetic equator can be explained by this drift. The velocities of two kinds of drift are deduced directly from the data. A reason for geographic control is described. It is shown that the seasonal anomaly of f0F2 cannot be accounted for only by the vertical drift. Therefore in order to explain the seasonal anomaly of f0F2 and other phenomena, (iii)-(iv), mentioned above, we suggest that there is at least the seasonal variation of the height distribution of the particle responsible for the F2 region.