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Geomagnetic pulsations in Pc5-6 band (~3-20 min) are persistent feature of ULF activity at dayside high latitudes. Magnetopause surface eigenmodes may be suggested as potential mechanism of these pulsations. One might expect the ground response of these modes to be near ionospheric projection of the open-closed field line boundary (OCB). Using data from instruments located at Svalbard we study transient geomagnetic response to impulsive "intrusion" of magnetosheath plasma into the dayside magnetosphere. These intrusions are triggered by modest changes of interplanetary magnetic field to southward, and observed as sudden shifts of equatorward red aurora boundary to lower latitudes and green line emission intensification. Each auroral disturbance is accompanied by burst of~1.7-2.0-mHz geomagnetic pulsations. Near-cusp latitudinal structure of ULF pulsations is compared with instant location of equatorward boundary of the red aurora, assumed to be a proxy of the OCB. Optical OCB latitude has been identified using data from the meridian scanning photometer. The latitudinal maximum of the transient geomagnetic response tends to be located near disturbed OCB proxy, within the error~1°-2°of the photometer and magnetometer methods. Recorded transient pulsations may be associated with the ground image of the magnetopause surface mode harmonic. Theoretical consideration indicates that after an initial excitation, surface large-scale mode converts into localized Alfvén oscillations and thus can exist for limited time only. Therefore, MHD surface modes in realistic inhomogeneous plasma cannot be considered in isolation, but as a combined system of modes with discrete and continuous spectra with irreversible transformation between them.

The St. Patrick's Day geomagnetic storm on March 17, 2015, has been chosen by the space community for synergetic analysis to build a more comprehensive picture of the storm's origin and evolution. This storm had an unusually long (~ 17 h) main phase. During this period, many substorm-like activations occurred. These activations resulted in bursts of geomagnetically induced currents (GICs) in power lines on the Kola peninsula. To examine the substorm activations in more detail, we apply various data processing techniques for the worldwide array of magnetometers: the virtual magnetograms, magnetic latitude-local time (MLT) snapshots, and magnetic keograms. These techniques are simple tools that are supplementary to more advanced facilities developed for the analysis of SuperDARN, IMAGE, and CARISMA arrays. We compare the global spatial localization and time evolution of the geomagnetic X-component disturbance and magnetic field variability measured by the Hilbert transform of time derivative dB/dt. The latitude-MLT mapping of these magnitudes shows that very often a region with highest magnetic variability does not overlap with a substorm "epicenter" but is shifted to its poleward or equatorward boundaries. Highest variability of the geomagnetic field, and consequently intense GICs, are caused by medium-scale fast varying structures. There is no one-to-one correspondence between substorm intensity and GIC magnitude.

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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.Keywords. Magnetospheric physics (MHD waves and instabilities; storms and substorms) -space plasma physics (kinetic and MHD theory)

The dynamics of intense ultra-low-frequency (ULF) activity during three successive strong magnetic storms during 29-31 October 2003 are considered in detail. The spatial structure of Pc5 waves during the recovery phases of these storms is considered not only from the perspective of possible physical mechanisms, but as an important parameter of the ULF driver of relativistic electrons. The global structure of these disturbances is studied using data from a worldwide array of magnetometers and riometers augmented with data from particle detectors and magnetometers on board magnetospheric satellites (GOES, LANL). The local spatial structure is examined using the IMAGE magnetometers and Finnish riometer array. Though a general similarity between the quasi-periodic magnetic and riometer variations is observed, their local propagation patterns turn out to be different. To interpret the observations, we suggest a hypothesis of coupling between two oscillatory systemsa magnetospheric magnetohydrodynamic (MHD) waveguide/resonator and a system consisting of turbulence + electrons. We propose that the observed Pc5 oscillations are the result of MHD waveguide excitation along the dawn and dusk flanks of the magnetosphere. The magnetospheric waveguide turns out to be in a meta-stable state under high solar wind velocities, and quasi-periodic fluctuations of the solar wind plasma density stimulate the waveguide excitation.