Modulation of equatorial electrojet irregularities by atmospheric gravity waves

On 9 January 2002 and 14 November 2001, the SAo Luis 30 MHz coherent backscatter radar observed unusual daytime echoes scattered from the equatorial electrojet. The electrojet echoing layers on these days, as seen in the range time intensity maps, exhibited quasiperiodic oscillations. Time-frequency decomposition of the magnetic field perturbations H, measured simultaneously by the ground-based magnetometers, also showed evidence of short-period waves. The ground-based observations were aided by measurements of the brightness temperature in the water vapor and infrared bands made by the GOES 8 satellite. The GOES 8 satellite measurements indicated evidence of deep tropospheric convection activities, which are favorable for the launch of atmospheric gravity waves (AGW) near SAo Luis. Our multitechnique investigation, combined with an analysis of the equatorial electric field and current density, indicates that AGW forcing could have been responsible, via coupling with E region electric fields, for the short-period electrojet oscillations observed over SAo Luis.