Height and latitude structure of electric fields and currents due to local east‐west winds in the equatorial electrojet

Abstract

Using the equivalent electrical circuit method for the theoretical treatment of the local wind effects on the equatorial electrojet, the height structures of electric fields and currents that are generated by height‐varying east‐west winds in the electrojet region have been calculated for theoretical model wind sturctures and for a variety of experimentally observed wind structures. The results bring out clearly the nature and extent of the local wind effects on the height and latitude structures of the equatorial electrojet. The more important conclusions of the present study are: (a) The vertical wind shears associated with tidal winds and gravity waves can generate significantly large electric fields and east‐west currents in the equatorial electrojet (EEJ). (b) The wind‐generated electric fields and currents are characterized by large height gradients, latitudinal gradients, and reversals of direction. (c) At the magnetic equator, wind‐generated electric fields and currents are often small (10%–30%) in comparison with the eastward electric‐field‐generated polarization field and east‐west currents around noon hours. (d) At geomagnetic latitudes of 3° and beyond the wind‐generated currents and electric fields often exceed those caused by the eastward electric field. (e) Beyond 2° the neutral winds can drastically alter the intensity and latitudinal structure of the EEJ, depending upon the magnitude and height location of the wind shear. (f) The observed variabilities in the ‘width’ and latitude structure of the EEJ can arise from the effects of such east‐west winds that have been observed experimentally.

Solar cycle dependent characteristics of the equatorial blanketing E<sub><i>s</i></sub> layers and associated irregularities

“…Apart from the general characteristics of E sb layers and that of VHF radar returns from them being different during solar minimum and maximum periods, certain other important aspects of the dominant physical processes controlling the growth processes of the gradient instabilities under varying solar activity conditions also appear to emerge from the present investigation. Some of the cases of radar returns from the E sb layers that are illustrated in the previous sections show that the velocity profiles of the type II irregularities associated with E sb layers show the presence of large velocity shears (Reddy and Devasia, 1981). As the occurrence of E sb layers are in general associated with very weak (almost zero) east-west electric field, these velocity shears in the Doppler velocity profiles are equivalent to wind shears.…”

“…As the occurrence of E sb layers are in general associated with very weak (almost zero) east-west electric field, these velocity shears in the Doppler velocity profiles are equivalent to wind shears. The presence of an E sb layer under the background conditions of a very weak east-west electric field and large shears in the Doppler velocity profiles of the type II irregularities associated with it suggest to the existence of highly structured wind-induced polarization electric field generated by the height varying zonal winds in the EEJ region (Reddy and Devasia, 1981). Some of the Doppler velocity profiles shown in the present studies have a close similarity to the reversal of drift velocity with height as shown by Reddy (1989).…”

“…However a later study by Reddy and Devasia (1981) showed that the local action of the east west winds with large vertical shears on the electrojet plasma could be responsible for the generation of the E sb layers. These vertical shears result in the generation of substantial wind induced polarization electric fields (E w ) (Reddy and Devasia, 1981). The wind-induced polarization electric fields in the same direction as the vertical polarization electric field due to E y can lead to the ionization convergence and hence the eventual formation of the E sb layers.…”

“…In one approach (Richmond, 1973;Reddy and Devasia, 1981;Stening, 1985;Anandarao and Raghavarao, 1987), it was suggested that the local interaction of height varying zonal winds with the electrojet plasma could generate polarization electric fields of sufficient magnitude and direction which in turn can modify the latitudinal and height structure of the electrojet current. The generation of a CEJ event can thus be viewed as resulting from an extreme case of wind interaction with the electrojet causing large wind generated polarization electric field (negative) to reduce the normal polarization electric field (due to E y ) in the EEJ.…”

Simulations of Wind Field Effect on Two-Stream Waves in the Equatorial Electrojet

“…That is, the thresh old value will be up-shifted when the wind field is par al lel to the elec tron drift ve loc ity, and con versely, the thresh old will be down-shifted when wind field is anti-par al lel to the elec tron drift ve loc ity. More over, past ob ser va tions and model cal cu la tions of neu tral wind in the equa to rial E re gion (e.g., Reddy and Devasia 1981;Larsen and Odom 1997;Hysell et al 2002) in di cate that the hor i zon tal wind field is mostly par al lel to the di rec tion of drift ve loc ity. If thresh old drift ve loc ity is not up-shifted by par al lel neu tral wind, and re mains the same at near the ion acous tic ve loc ity, then two-stream ) for that col umn, while the la bels on the left give k z (in m -1 ) for that row.…”