ISSN:
1365-246X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
The study of rocket measurements suggests the following conclusions, (i) Ionospheric currents are basically in two layers, (ii) The upper current layer with a steady altitude extent of 18 ± 3 km is global and should be regarded as the worldwide part of the Sq current system, (iii) The intense eastward lower current layer at the magnetic dip equator that terminates in a focus within 2° to 4° dip latitude, together with the reverse westward lower current layer that peaks around 5.3 ± 0.7° dip latitude, should be regarded as the equatorial electrojet (EEJ). (iv) The EEJ and the worldwide part of the Sq current system are coupled, sometimes overlapping in varying degrees, especially within 0° to 0.5° dip latitude where the overlap often leads to a hybrid current system, (v) The lunar geomagnetic variations result from the modulations of the above current layers and not from a separate current layer. An interesting latitudinal profile of the vertical cross-section of ionospheric currents from the dip equator to about 60° latitude has been presented. Seven of the nine altitude structure parameters of the current layers equatorward of the EEJ current focus differ by 10 to 30 km from their values beyond the EEJ current focus. Six of these altitude parameters tend to recover after their minima at the EEJ current focus and the Sq current focus. The lower current layer is thicker, the upper current layer is higher, and the entire current system is thicker equatorward of the EEJ current focus than beyond it. The half thickness at half of the peak current density of the eastward EEJ is about 2.9 times that of the reverse westward lower current layer, and about 34.3 ± 0.7 per cent greater than that of the worldwide part of the Sq current layer equatorward of the Sq current focus. The continuous distribution of current density model has elucidated the latitudinal variations of ΔF, ΔH and their ratio in the vicinity of the dip equator. It thus explains some observations of Davis, Burrows & Stolarik (1967) and some discrepancies that accompanied the detection of the meridional currents of the equatorial electrojet.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-246X.1992.tb04645.x
Permalink
