Investigation of the ground-based signatures of the ionospheric Alfven resonator (IAR) using the data from EISCAT Svalbard radar

Semenova, N. V. and Yahnin, A. G.

Polar Geophysical Institute, Apatity, Russia

The spectra of the electromagnetic noise in frequency range of 0.1-10 Hz are sometimes exhibit a resonance structure with frequency scale of few tenths to 1-2 Hz. This spectral resonant structure (SRS) is believed to be an observable signature of the ionospheric Alfven resonator (IAR). According to the IAR theory, characteristics of SRS depend on parameters of the upper ionosphere, particularly on the electron density in the F-layer maximum, altitudinal scale of the density decay above the maximum, and the conductivity in the E-layer. The morphology of SRS have been studied at low, middle, and auroral zone latitudes and showed a general agreement with the theory. Recently the SRS observations were performed at high latitudes, in Barentsburg on Svalbard using the search coil magnetometer of the Polar Geophysical Institute. An advantage of this location is in closeness with the EISCAT Svalbard radar that provides information on the height distribution of the ionospheric parameters. In the cases when radar data are available during SRS observations we performed calculations of the IAR eigenfrequencies on the basis of measurements of the electron density altitudinal profiles. Obtained values are in a good agreement with frequencies and frequency scale of SRS. This confirms IAR as the origin of SRS. We also compared statistical properties of SRS in Barentsburg with predictions made on the basis of the IAR theory and the electron density altitudinal profiles revealed from the Incoherent Scatter Radar Ionospheric Model (ISRIM). As the result, some disagreement between calculations and observations is found. Thus, the observations show very low occurrence of SRS in the daytime, while calculations suggest almost equal occurrence during day and night. This disagreement is explained by enhanced changeability of the ionosphere in the daytime, when the ionosphere above the station is undergone an influence of transient precipitation, fields, and currents related to the cusp and various boundary layers, in comparison with night conditions, when the station is situated well poleward of the auroral oval. The changeability is not accounted by ISRIM, but affects the SRS magnetic observations, which require a stability of the ionospheric parameters at least for some tens of minutes.