WAVE CHARACTERISTICS OF DAYTIME AND NIGHTTIME PI-2 PULSATIONS AT THE EQUATORIAL AND LOW LATITUDES

Peculiarities of daytime and nighttime Pi 2 pulsations at the dip equa tor are examined by using multipoint measurements from the 210 degrees magnetic meridian (MM) magnetometer network. We found that during day time the amplitude of Pi 2 pulsations at the dip equator iis enhanced, and the phase lags similar to 34 degrees behind those at low-latitude (magnetic latitude Phi = 19.5-46.2 degrees) stations. On the other ha nd, during nighttime the amplitude nf Pi 2 pulsations at the dip equat or is depressed, and the phase lags similar to 18 degrees behind those at the lower latitudes. Because the zonal ionospheric conductivity at the dip equator is much higher than that at the off-dip equator regio n, Pi 2 signals are expected to be distorted more effectively at the d ip equator. The observations imply that the daytime and nighttime Pi 2 pulsations in the equatorial and low-latitude regions can be Explaine d by invoking an instantaneous penetration of electric field variation s from the nightside polar ionosphere to the dayside equatorial ionosp here, and a direct incidence of compressional oscillations from the ni ghtside inner magnetosphere, respectively.