Seasonal Anomalies in Ionospheric F2-Layer at Conjugate Places

Abstract

Seasonal anomalies in the disturbed-day variations of <i>f₀</i>F2 are described for the same stations, data for, which, under normal conditions, were analyzed by the authors in an earlier paper <i>(Indian J.Radio space phys.,2. </i>, (1973), 22). It is shown that <i>f₀</i>F2 increases markedly at both the conjugate places during a northern winter month (December) although summer conditions prevail in the south. Further, the northern stations show more clearly the increase of <i>f₀</i>F2 in winter and decrease in summer than at southern stations where increases as well as decreases are found in either season. However, the annual average DS variation shows increased values of <i>f₀</i>F2 for most of the time in the south. In contrast, the DS variation of the horizontal component of the-earth's magnetic field <i>(H-</i> field) is in phase opposition to that of <i>f₀</i>F2 in the south, but not so in the north, although the magnitude of H-field variation is larger in the northern winter month at both the conjugate places than in the southern winter month. The results indicate that besides electromagnetic drift of F2-ionizittion, the neutral wind-associated vertical drift of ionization and the change in gas composition brought about by the thermospheric heating and air circulation might be effective in causing the changes in the F2-ionization on magnetically disturbed· days at places with a magnetic dip of 40° to 60°. However, electromagnetic drift forces are more pronounced at low latitudes.