A Statistical Study of Poleward Traveling Ionospheric Disturbances Over the African and American Sectors During Geomagnetic Storms

We present statistical results of traveling ionospheric disturbances (TIDs) with origin near the geomagnetic equator during geomagnetic storms that occurred within the period of 2010-2018. Based on storm criteria of Kp > 4 and Dst <= -50 nT, we have analyzed total electron content perturbations derived from Global Navigational Satellite Systems observations within a latitude range of 40 degrees S-60 degrees N and longitude ranges of 20 degrees-40 degrees E and 50 degrees-70 degrees W representing the African and American sectors. Although the northern hemispheric part of the African sector has limited data coverage, results show that the launched TIDs do not exceed the latitudinal distance of 20 degrees-25 degrees from their origin during the analyzed period. A statistically similar result is observed over the American sector with launched poleward TIDs constrained largely within +/- 20 degrees-30 degrees around the geomagnetic equator. Where data are available, majority of these cases are linked to changes in ionospheric electrodynamics, especially the enhancement of equatorial electrojet (EEJ), although there are other observations that are not explained by EEJ variability. This indicates that there may be other physical mechanisms that play a role in launching TIDs at the geomagnetic equator during disturbed conditions. An important result is that large-scale and medium-scale TIDs have been found to occur predominantly during the main and recovery phases of geomagnetic storms, respectively, at least over the African sector.