PHASE-RELATIONSHIPS BETWEEN TOTAL ELECTRON-CONTENT VARIATIONS, DOPPLER VELOCITY OSCILLATIONS AND GEOMAGNETIC-PULSATIONS

The phase relationship between variations of ionospheric total electro n content (TEC) and ground-level ULF geomagnetic pulsations has been e xamined for the advection and compression mechanisms. To determine the causal mechanism, several earlier studies have examined the phase dif ference between oscillations of Doppler velocity in ionospherically re flected radio waves and simultaneous ULF geomagnetic pulsations. In mo st instances it was found that the phase relation varied from event to event. With the application of Euler's formula this study shows that in low geomagnetic and midgeomagnetic latitudes the phase differences between variations of TEC and ULF pulsations in the northward componen t of the geomagnetic field due to the advection and compression mechan isms are 0 degrees and 180 degrees, respectively. We also found that T EC variations tend to lead ionospheric Doppler velocity oscillations b y 90 degrees. Furthermore, it is shown that the phase relationship bet ween ionospheric Doppler velocity oscillations and ULF pulsations of t he northward component of the geomagnetic field, caused by the advecti on and compression mechanisms, are functions of the scale length, freq uency of ULF waves, and geomagnetic dip.