Asymmetry between theF₂region of the ionosphere in the northern and southern hemispheres

Abstract

The paper describes the asymmetry in the seasonal variations of the critical frequency of the F2 layer at high‐latitude stations in the northern and southern hemispheres during the years of minimum sunspot number. The variations of the F2 layer at pairs of stations similarly situated on opposite sides of the equator are studied for different hours of the day and for different stages of solar activity. During years of low sunspot number, the curves of seasonal variations of foE, foF1 as well as foF2 are very similar to each other, and the well known summer decrease of noon foF2 is not present at southern stations. The various hypotheses advanced to explain the abnormalities in the F2 region are examined to explain the asymmetry, and a plausible cause is suggested on the basis of wind systems in the F2 region, mainly the horizontal transport of the ionization.

Cause of the midlatitude winter night increase inf0F2

“…Yet the density is observed to start increasing two hours before midnight and to continue to do so until about three hours after midnight (Figures 2-4). At European stations the nighttime increase tends to occur earlier and actually peaks at midnight [Rastogi, 1960a]. Figure 15, which has been taken from the paper by Rastogi.…”

“…The similarity in the behavior at these two stations suggests that the local summer behavior at one point is very like that at a conjugate station. Ilence, in the absence of a conjugate station, the behavior observed in June at one station may be tak.en as the behavior in December at its conjugate point [after Rastogi, 1960a]. and geographic equators.…”

High-order ionospheric effects on electron density estimation from Fengyun-3C GPS radio occultation

“…6, we can see that the green circles lie above the red circles, especially in panels b and c, which means that in the same latitude area, the residual TEC in the Northern Hemisphere is larger than that in the Southern Hemisphere. As we know, the electron density distributes in symmetry to the magnetic equator, and the geomagnetic equator lies on the northern side of the geodetic equator (Rastogi, 1960;Kil et al, 2011), so in some places, the double peak values of electron density are both in the low-latitude area of the Northern Hemisphere. Therefore, if we fix the latitude value, the high-order ionospheric effects are more obvious in the Northern Hemisphere.…”