Frequency dependence of equatorial electrojet effect on geomagnetic micropulsations

The micropulsation data (Pc3–Pc4 range) from off-equatorial and equatorial stations Alibag (ABG) and Tirunelvelli (TIR) in the Indian zone during 1991 are analysed for delineating the electrojet effect. The ratios of the spectral amplitudes at significant frequency bands the horizontal component of the magnetic field at TIR to that at ABG are worked out as a function of frequency. The results show that the lower frequencies undergo larger equatorial amplification. However, above a certain frequency the pulsation signal is found to attenuate rather than exhibit the general enhancement. The ratio becomes minimum around the period, 18 to 24 sec. At further higher frequencies, there is again the normal electrojet amplification. The explanation of such a behaviour of the electrojet on the pulsation amplitude is rather difficult at the present stage and to some extent becomes controversial even if it is offered.