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Ionospheric and Solar Wind Variation during Magnetic Storm Onset and Main Phase at Low- and Mid-latitudes

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Adekoya B. J. , Adebesin B. O.

Acta Geophysica

2015

tom Vol. 63, no. 4

1150--1180

The relationship between the F2-layer critical frequency and solar wind parameters during magnetic storm sudden commencement (SSC) and main phase periods for intense (IS) and very intense (VIS) class of storms is investigated. The analysis covers low- and mid-latitude stations. The effects of ionospheric storm during SSC period is insignificant compared to the main phase, but can trigger the latter. The main phase is characterized by severe negative storm effect at both latitudes during VIS periods while it is latitudinal symmetric for IS observations. The IS reveal positive/negative storm phase in the low-/mid-latitudes, respectively. Ionization density effect is more prominent during VIS events, and is attributed to large energetic particle and solar activity input into the earth magnetosphere. However, ionospheric effect is more significant at the low-latitude than at the mid-latitude. Lastly, ionospheric storm effect during a geomagnetic storm may be related to the combinational effect of interplanetary and geomagnetic parameters and internal ionospheric effect, not necessarily the solar wind alone.

Quantifying the EEJ current with ground-based ionosonde inferred vertical E × B drifts in the morning hours over Ilorin, West Africa

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Adeniyi J. O. , Adimula I. A. , Adebesin B. O. , Reinisch B. W. , Oladipo O. A. , Olawepo O. , Yumoto K.

Acta Geophysica

2014

tom Vol. 62, no. 3

656--678

The relationship between the ground-based inferred vertical E × B drifts, Vz, and the magnetic equatorial electrojet current during the year of solar minima was presented. Both the diurnal and seasonal Vz variations are positively directed during the daytime and negative at nighttime. The evening time pre-reversal enhancement occurs around 19:00 LT. The fairly strong linear relationship between the electrojet current strength and Vz exhibited higher correlations during the daytime (06:00-16:00 LT). The maximum morning time proxy parameter described by E = [d (ΔHILR)/dt]max in the morning hours, indicating the east-west electric field in the EEJ, corresponds reasonably well with the E × B drift and, hence, can be used as a proxy parameter for representing Vz in the morning hours. The daytime EEJ magnitude seasonal changes are connected with a change in conductivity emerging from the action of turbulence and divergence of momentum flux. These waves above the dynamo region are suggested to lead to partial counter electrojet during the equinoctial months.