Measurement and interpretation of power spectrums of ionospheric scintillation at a sub-auroral location

Abstract

A study of the power density spectrum of ionospheric scintillation of a radio star and satellites, at a subauroral location, has revealed the following: (1) Scintillations generally display a ‘pink’ noise spectrum, with almost uniform spectral density at frequencies below ∼0.01 Hz, and decreasing spectral density at frequencies above this value. (2) At frequencies ƒ ≳ 0.01 Hz, the power spectrum varies as ƒ−n, with n being typically 2.7 (i.e., a decrease of 8 db per octave). (3) The width of the spectrum displays a diurnal variation such that, on the average, higher scintillation frequencies are observed at night than during the day. These results have been examined in the context of existing theories involving electrodynamic or hydromagnetic processes, in an attempt to establish the source of the ionospheric irregularities. Although many theories suggest that hydromagnetic waves are responsible for the observed irregularities, they leave the precise nature of the interaction in doubt. It is noted that the spectrum of geomagnetic micropulsations is in substantial agreement with the scintillation power spectrum, and, therefore, a theory is developed tying the two phenomena together. A model is proposed in which horizontally ducted hydromagnetic waves produce irregularities in the F region and geomagnetic micropulsations, causing both to have the same power law spectrum.