A Study of Ionospheric Hemispheric Asymmetry Observed by CODE GIM, IRI, and FORMOSAT‐3/COSMIC

This paper studies the hemispheric asymmetry of the total electron content (TEC) by means of the Global Ionosphere Map (GIM), which has been routinely publishing every 2 hours by the Center for Orbit Determination in Europe (CODE) during 1999-2019. The study period including the solar cycles 23 and 24 allows us globally uniformly examine the ionospheric asymmetry phenomenon of the GIM TEC in the different solar activities. At each time point, summations of the GIM TEC at low-, mid-, and high-latitude in the northern and southern hemispheres are computed. This study compares the sums of the two hemispheres in various local times, months, and solar activities. By computing the annual magnitude of the asymmetry phenomenon, it is found that the asymmetric phenomenon is more prominent during low solar activity, although its fluctuation is proportional to the F10.7 index. We further study the asymmetry phenomenon in various latitudes and find the latitudes with prominent signatures. The study also validated the hemispheric asymmetry of the total electron content using the International Reference Ionosphere (IRI) model and compared the differences and mechanisms of the hemispheric asymmetry phenomena in NmF2 and hmF2 by IRI and FORMOSAT‐3.