Experimental scientists have indicated that an in-phase relationship between measurements of ionospheric Doppler velocity oscillations and ULF pulsations in the northward component of the geomagnetic field on the ground results from the compressional mechanism. A careful study of the theoretical models developed previously, however, shows that in low and middle geomagnetic latitudes, owing to the compressional mechanism the ionospheric Doppler velocity oscillations lead the ULF pulsations in the northward component of the geomagnetic field at ground level by 90-degrees.
