Some Anomalous Features of the Ionospheric F2-Layer at Low Latitude Conjugate Places

Abstract

The diurnal variation of the F2-layer critical frequency <i>(f0</i>F<i>2) </i> is compared with the diurnal variations of the horizontal component <i>H </i> of the earth's magnetic field and of the declination <i>D </i> at a pair of low latitude conjugate stations in the Pacific and the Atlantic zones for a medium-low solar activity period. It is shown that the day-time bite-out in <i>f0</i>F<i>2 </i> and its seasonal anomaly are dependent on the characteristic daily variation of the H-field. There is also an indication of the effect of E-W declination on the diurnal variation of <i>f0</i>F<i>2 </i> at places near magnetic dip 45_50° as explained by H. Kohl, J. W. King & D. Eccles [<i>J. atmos. terr. Phys., 31 </i> (1969), 1011]; such effect is not observed at low latitudes.<br> The day-time depression in <i>f</i>0F<i>2</i> seems to be more pronounced at Port Stanley in summer than at its northern conjugate Puerto Rico, perhaps because of the additional effect of the neutral wind-associated vertical drift of ionization, for which the situation of Port Stanley (mean magnetic dip= 46.3') is very favourable.