The Determination of the Mechanisms of Ionospheric ULF Oscillations


Variations of ionospheric total electron content (TEC) and/or oscillations of ionospheric Doppler velocity are frequently observed in association with ultra low frequency (ULF) geomagnetic pulsations. Theoretical and numerical models have been developed to study these ionospheric signatures of pulsations. Extending the previous models and with the application of a linear perturbation method, this study shows that the phase differences between variations of TEC and ULF pulsations in the northward component of the geomagnetic field due to the advection and compression mechanisms are 0¢X and 180¢X, respectively. It is also shown that ionospheric Doppler velocity oscillations lag and lead by 90¢X ULF pulsations of the northward component of the geomagnetic field, also caused by the advection and compression mechanisms. Furthermore, we find that TEC variations tend to lead ionospheric Doppler velocity oscillations by 90¢X.

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