Marcin Grzesiak

Ionospheric Alfvén resonator as seen by Freja satellite

Sharp increase of the Alfven speed above the ionosphere is expected to create a resonant cavity for the Alfven waves traveling along the geomagnetic field lines (so-called Ionospheric Alfven Resonator). The wavelet transform has been used to analyze magnetic and electric fields recorded on Freja satellite. Cross-phase spectra between field components in the frequency range 0.5–10 Hz reveal a pattern similar to that predicted theoretically for the resonator. The Fourier cross-phase spectra fail to show any characteristic features. We conclude that this is due to the spatial structure of the resonator which can be examined only with local analysis techniques.

Identification of the dominant ULF wave mode and generation mechanism for obliquely propagating waves in the Earth's foreshock

We discuss mechanisms of the generation of ultralow frequency (ULF) upstream waves in the terrestrial foreshock that are essential for the acceleration of ions in space plasmas. The analysis is based on global hybrid kinetic simulations of the magnetosphere that provide realistic environment for the growth of the ULF waves in a quasi-radial configuration of the interplanetary magnetic field. We focus on a long-debated problem of the generation mechanism of oblique and parallel ULF waves and provide quantitative arguments in favor of the ion/ion cyclotron resonant instability. We also show that parallel propagating waves are predominantly generated in this configuration, but geometrical effects related to the phase space density in wave vector space lead to apparent predominance of obliquely propagating waves. Correspondence between the results outlined above and previously published experimental claims is thoroughly discussed and our results are shown to be consistent with spacecraft measurements.

Solar Terminator-Related Ionosphere Derived from GPS TEC Measurements: A Case Study

We present a case study of ionospheric wave activity during solar terminator crossing using GPS TEC measurements. As a basic tool, the spatial gradient of total electron content (TEC) has been used. We tested with positive result the hypothesis on anisotropic response to assumed one-dimensional solar terminator forcing. The approximate drift velocity of irregularities has been computed. The wavelet analysis gave an interesting insight into variable frequency content of TEC gradient time series. We also proposed a filtering with respect to spatial scale allowing for resolving the spatio-temporal ambiguity.