Modulation of equatorial electrojet plasma waves by overshielding electric field during geomagnetic storms

This brief report presents daytime 30 MHz radar observations of equatorial electrojet plasma irregularities in Sao Luis, Brazil, during the 10 January 2002, 4 September 2002, and 6 November 2001 geomagnetic storms. Modulation of equatorial electrojet plasma waves by the overshielding electric field is detected by the radar during the January and September storm events. The depressions of radar echo intensity observed by the Sao Luis radar during the 10 January and 4 September 2002 storms are caused by inhibition of large-, medium-, and short-scale electrojet plasma waves by the overshielding electric field. Corresponding to the depressions of the radar echoes, counter equatorial electrojets were observed by ground-based magnetometer in Sao Luis. The influences of disturbance dynamo, undershielding, and overshielding electric fields on the equatorial electrojet irregularities and current have been evident on the 6 November 2001 radar and magnetic field data. This study demonstrates the control of the equatorial electrojet plasma waves (growth and suppression) by the interplanetary magnetic field and also the coupling between the high-latitude and equatorial ionospheres.