Phase characteristics of geomagnetic micropulsations

Midlatitude geomagnetic micropulsations in the 15- to several-hundred-second period range were recorded simultaneously at stations separated a few hundred kilometers in east-west and north-south directions. Diurnal patterns of phase difference between stations were detected in which the station nearer the dark hemisphere usually led in phase. The magnitude of the phase lags is shown to be a function of period. Although absolute phase velocities could not be determined, the dispersive properties of the propagation medium were investigated. Apparent phase velocity curves were constructed from measurements of phase lags of many micropulsation signals recorded at all hours of the day and night. In addition, Fourier transform analysis of isolated Pt type signals permitted determination of apparent phase velocity and apparent group velocity curves of single signals. Apparent phase velocity increases with decreasing period. Energy propagation of Pt's is associated with a group velocity maximum. Uncertainty of the proper sign of the apparent group velocity prohibits a deduction of diurnal patterns of energy propagation from the diurnal phase lag patterns.