Abstract
Abstract. The dynamics of global Pc5 waves during the magnetic storms on 29–31 October 2003 are considered using data from the trans-American and trans-Scandinavian networks of magnetometers in the morning and post-noon magnetic local time (MLT) sectors. We study the latitudinal distribution of Pc5 wave spectral characteristics to determine how deep into the magnetosphere these Pc5 waves can extend at different flanks of the magnetosphere. The wave energy transmission mechanisms are different during 29–30 October and 31 October wave events. Further, we examine whether the self-excited Kelvin–Helmholtz instability is sufficient as an excitation mechanism for the global Pc5 waves. We suggest that on 31 October a magnetospheric magnetohydrodynamic (MHD) waveguide was excited, and the rigid regime of its excitation was triggered by enhancements of the solar wind density. The described features of Pc5 wave activity during recovery phase of strong magnetic storm are to be taken into account during the modeling of the relativistic electron energization by ultra-low-frequency (ULF) waves.
Highlights
Geomagnetic ULF Pc5 waves are a persistent component of a disturbed magnetosphere
It was supposed that the main source of Pc5 pulsations is the Kelvin–Helmholtz instability (KHI) of the magnetopause engulfed by the solar wind (SW) flow (Yumoto and Saito, 1980; Kivelson and Pu, 1984)
One of the main difficulties in applying Pc5-driven diffusion/energization mechanisms to electron dynamics is the mismatch of their latitudinal distribution: electron energization starts in the middle magnetosphere (L ∼ 3–4), and expands to higher latitudes (L ∼ 6–7), whereas typical Pc5 waves are strongly localized at sub-auroral latitudes and hardly can be detected at middle latitudes
Summary
The intensity of Pc5 waves is strongly dependent on magnetic local time (MLT) and on geomagnetic latitude as well. The 360◦ profile shows that at low latitudes Pc5 wave activity experiences an additional enhancement of the spectral power at < 50◦ upon approaching the equatorial region (Fig. 5d). In the morning sector ( ∼ 330◦) in the region with narrow amplitude peak ( ∼ 67◦), the latitudinal phase dependence has a gradient ( φ ∼ 60◦), corresponding to an apparent poleward phase propagation This feature is characteristic of Alfvén field-line resonance. In the afternoon sector ( ∼ 110◦) in the region of the high-latitude maximum of Pc5 power (∼ 63◦–67◦), the phase does not depend on latitude This maximum cannot be associated with the field-line resonance, as was indicated by Kleimenova and Kozyreva (2005). During the time interval with largest Pc5 activity (11:00– 12:00 UT), even a visual comparison of magnetograms (X component) (Fig. 6) shows westward propagation both in the morning and afternoon sectors. Much larger response of magnetospheric oscillatory response during magnetic storm confirms the proposed conception of the triggered excitation of the magnetospheric system near the instability threshold
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