DP-2 ELECTRIC-FIELD FLUCTUATIONS IN THE DUSK-TIME DIP EQUATORIAL IONOSPHERE

We have studied the geomagnetic and ionospheric manifestations of the DP 2 activity that occurred on April 7, 1995 using high time resolutio n magnetometer data of IMAGE network in Scandinavia and of Alcantara ( dip 1.2 degrees N), Brazil, and F layer vertical plasma drift, V-z, me asured by an HF Doppler radar at Kodaikanal(dip 4 degrees N), India. Q uasi-periodic fluctuations in dusk-time (1730-1900 LT) F layer vertica l plasma drift (eastward electric field) occurred over Kodaikanal cohe rent with DP 2 type magnetic fluctuations (period approximate to 25 mi n) at the day-side dip equator and auroral/subauroral latitudes. This first-ever observation at the dusk-side equator is in agreement with t he two-cell equivalent current system previously proposed for DP 2 flu ctuations. The results strongly suggest that the magnetospheric electr ic field responsible for DP 2 fluctuations penetrates to equatorial io nosphere on the dusk-side as on the day-side. An additional observatio n is that the electric field fluctuation amplitude increases towards t he nightside suggesting the influence of duck sector electrodynamics i n the observed signature of the DP 2 electric field.