PI2 PULSATIONS AT SEPARATED SITES (DELTA-PHI-SIMILAR-OR-EQUAL-TO-90-DEGREES) - A COMPARISON BETWEEN MIDLATITUDE AND LOW-LATITUDE OBSERVATIONS

A comparison between geomagnetic field measurements made during July 1985 at Green Hill (R.I., USA, geomagnetic latitude LAMBDA is-approximately-equal-to 52-degrees) and L'Aquila (Italy, LAMBDA is-approximately-equal-to 42.5-degrees) at longitudinal separations of the order of 90-degrees reveals a close correspondence between mid- and low-latitude measurements in the identification of Pi2-type pulsations when both stations are in the night sector. The observed azimuthal delay times between the two stations are smaller than previously estimated. The polarization pattern is found to be anticlockwise at both stations and does not show any LT dependence. However a clear LT control of the orientation of the major axis of the polarization ellipses emerges at low latitudes. A comparison of observations during intervals in which one station is located in the dayside hemisphere and one is located in the nighttime hemisphere suggests the occurrence of dayside Pi2-like events at mid- and low-latitudes.