Abstract. In this paper, in terms of an axisymmetric model of the magnetosphere, we formulate the criteria for which the Alfvén waves in the magnetosphere can be toroidally and poloidally polarized (the disturbed magnetic field vector oscillates azimuthally and radially, respectively). The obvious condition of equality of the wave frequency ω to the toroidal (poloidal) eigenfrequency T N ( P N ) is a necessary and sufficient one for the toroidal polarization of the mode and only a necessary one for the poloidal mode. In the latter case we must also add to it a significantly stronger condition, where m is the azimuthal wave number, and N is the longitudinal wave number. In cold plasma (the plasma to magnetic pressure ratio β = 0) the left-hand side of this inequality is too small for the routinely recorded (in the magnetosphere) second harmonic of radially polarized waves, therefore these waves must have nonrealistically large values of m. By studying several models of the magnetosphere differing by the level of disturbance, we found that the left-hand part of the poloidality criterion can be satisfied by taking into account finite plasma pressure for the observed values of m ∼ 50 − 100 (and in some cases, for even smaller values of the azimuthal wave numbers). When the poloidality condition is satisfied, the existence of two types of radially polarized Alfvén waves is possible. In magnetospheric regions, where the function P N is a monotonic one, the mode is poloidally polarized in a part of its region of localization. It propagates slowly across magnetic shells and changes its polarization from poloidal to toroidal. The other type of radially polarized waves can exist in those regions where this function reaches its extreme values (ring current, plasmapause). These waves are standing waves across magnetic shells, having a poloidal polarization throughout the region of its existence. Waves of this type are likely to be exemplified by giant pulsations. If the poloidality condition is not satisfied, then the mode is toroidally polarized throughout the region of its existence. Furthermore, itCorrespondence to: D. Yu. Klimushkin (klimush@iszf.irk.ru) has a resonance peak near the magnetic shell, the toroidal eigenfrequency of which equals the frequency of the wave.

Magnetohydrodynamic (MHD) oscillatory processes in different plasma systems, such as the corona of the Sun and the Earth's magnetosphere show interesting similarities and differences, which so far received little attention and remain underexploited. The successful commissioning within the past ten years of SDO, Hinode, STEREO and THEMIS spacecraft, in combination with matured analysis of data from earlier spacecraft (Wind, SOHO, ACE, Cluster, TRACE and RHESSI) makes it very timely to survey the breadth of observations giving evidence for MHD oscillatory processes in solar and space plasmas, and state-of-the-art theoretical modelling. The paper reviews several important topics, such as Alfvénic resonances and mode conversion; MHD waveguides, such as the magnetotail, coronal loops, coronal streamers; mechanisms for periodicities produced in energy releases during substorms and solar flares, possibility of Alfvénic resonators along open field lines; possible drivers of MHD waves; diagnostics of plasmas with MHD waves; interaction of MHD waves with partly-ionised boundaries (ionosphere and chromosphere). The review is mainly oriented to specialists in magnetospheric physics and solar physics, but not familiar with specifics of the adjacent research fields.

[1] A previous case study observed a ULF wave with an eastward and equatorward phase propagation (an azimuthal wave number m, of ∼13) generated during the expansion phase of a substorm. The eastward phase propagation of the wave suggested that eastward drifting energetic electrons injected during the substorm were responsible for driving that particular wave. In this study, a population of 83 similar ULF wave events also associated with substorm-injected particles have been identified using multiple Super Dual Auroral Radar Network radars in Europe and North America between June 2000 and September 2005. The wave events identified in this study exhibit azimuthal wave numbers ranging in magnitude from 2 to 92, where the direction of propagation depends on the relative positions of the substorm onsets and the wave observations. We suggest that azimuthally drifting energetic particles associated with the substorms are responsible for driving the waves. Both westward drifting ions and eastward drifting electrons are implicated with energies ranging from ∼1 to 70 keV. A clear dependence of the particle energy on the azimuthal separation of the wave observations and the substorm onset is seen, with higher energy particles (leading to lower m-number waves) being involved at smaller azimuthal separations.Citation: James, M. K., T. K. Yeoman, P. N. Mager, and D. Y. Klimushkin (2013), The spatio-temporal characteristics of ULF waves driven by substorm injected particles,

Abstract. A case study of SuperDARN observations of Pc5Alfvén ULF wave activity generated in the immediate aftermath of a modest-intensity substorm expansion phase onset is presented. Observations from the Hankasalmi radar reveal that the wave had a period of 580 s and was characterized by an intermediate azimuthal wave number (m=13), with an eastwards phase propagation. It had a significant poloidal component and a rapid equatorward phase propagation (∼62 • per degree of latitude). The total equatorward phase variation over the wave signatures visible in the radar field-of-view exceeded the 180 • associated with field line resonances. The wave activity is interpreted as being stimulated by recently-injected energetic particles. Specifically the wave is thought to arise from an eastward drifting cloud of energetic electrons in a similar fashion to recent theoretical suggestions Zolotukhina et al., 2008;Mager et al., 2009). The azimuthal wave number m is determined by the wave eigenfrequency and the drift velocity of the source particle population. To create such an intermediate-m wave, the injected particles must have rather high energies for a given L-shell, in comparison to previous observations of wave events with equatorward polarization. The wave period is somewhat longer than previous observations of equatorward-propagating events. This may well be a consequence of the wave occurring very shortly after the substorm expansion, on stretched near-midnight field lines characterised by longer eigenfrequencies than those involved in previous observations.

Abstract. We analyzed the spectral-polarized characteristics of Pc5 ULF waves observed on 17 September 2000 after the 03:20:25 UT substorm onset with the satellites GOES 8 and 10 located east and west of the onset location. In the course of the event, the wave polarization changed from mixed (between toroidal and poloidal) to poloidal, and then to mixed again. The hodogram of magnetic field oscillations rotated counterclockwise at GOES 8, and clockwise at GOES 10. It is suggested that the satellites detected the waves generated by the substorm injected clouds of the charged particles drifting in the magnetosphere in the opposite azimuthal directions: GOES 8 (located east of the substorm onset) detected the wave generated by an electron cloud, and GOES 10 (west of the onset) detected the wave generated by a positive ion cloud. This interpretation is confirmed by the energetic particles data recorded by LANL satellites.

Abstract. The structure of monochromatic MHD-waves with large azimuthal wave number m ) 1 in a twodimensional model of the magnetosphere has been investigated. A joint action of the ®eld line curvature, ®nite plasma pressure, and transversal equilibrium current leads to the phenomenon that waves, standing along the ®eld lines, are travelling across the magnetic shells. The wave propagation region, the transparency region, is bounded by the poloidal magnetic surface on one side and by the resonance surface on the other. In their meaning these surfaces correspond to the usual and singular turning points in the WKB-approximation, respectively. The wave is excited near the poloidal surface and propagates toward the resonance surface where it is totally absorbed due to the ionospheric dissipation. There are two transparency regions in a ®nite-beta magnetosphere, one of them corresponds to the Alfve n mode and the other to the slow magnetosound mode.

[1] The polarization and field-aligned structure of drift-compressional modes and the corresponding plasma instability are studied in a gyrokinetic framework in the axisymmetric model of the magnetosphere with isotropic plasma. The plasma is assumed to be composed of core cold particles and an admixture of hot protons, with an inverted distribution of hot protons. Such plasma experiences a compressional resonance when the wave frequency is equal to an eigenfrequency of the drift-compressional mode. In this resonance, the wave is dominated by the field-aligned and azimuthal magnetic field components and is narrowly localized along the field line at the equator, the same as the plasma to magnetic pressure ratioˇ. The plasma instability occurs when the temperature diamagnetic drift velocity is less than the magnetic drift velocity or opposite in direction. Furthermore, the narrower the inverted distribution, the higher the instability growth rate and the smaller the value ofˇrequired for the instability to occur. The growth rate reaches its highest values when a positive radial temperature gradient and a negative radial density gradient occur simultaneously.

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