New instrumentation, along with new analysis and modelling techniques, have greatly enhanced our understanding of ULF wave phenomena in recent years. This paper presents a brief review of some of the highlights of progress made in the last two years on observational and modelling studies of ULF waves in the Earth's magnetosphere and ionosphere at equatorial to mid-latitudes. Recent research focused on the Pc3 range has employed new arrays and timeseries analysis techniques to characterise the low latitude magnetospheric response. Recent research into Pi2 waves has concentrated on their potential candidacy as magnetospheric cavity mode signatures. A view on some of the forthcoming opportunities for new research into ULF waves is given.

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In order to clarify the correlation of high- and low-latitude Pi 2 magnetic pulsations, we have analyzed 1-s magnetic data from the Chokurdakh (Φ =64.75°, L = 5.50), Magadan (Φ= 53.70°, L =2.85), and Moshiri (Φ = 37.76°, L = 1.60) stations along the 210° magnetic meridian. The H-component Pi 2 amplitudes are of almost the same order in the plasmasphere. In the outside region of the plasmapause the H-component amplitudes become roughly 1 order larger than those of in the plasmasphere. The D-component amplitudes, on the other hand, increase exponentially from lower to higher latitudes. At L = 1.60-2.85 the H- and D-component Pi 2 amplitudes show in-phase relation. Between L = 2.85 and 5.50, the Hcomponents have a roughly out-of-phase relation, while the D components show an unclear relation. These observations suggest that Pi 2 pulsations consist of several different modes in the structured magnetosphere.

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At the Yakut chain stations in the subauroral zone (L ∼ 3-4) Pil pulsations within 0.5-5 Hz frequency range have been revealed by the active band-pass filters. They are observed during intense geomagnetic disturbances (K≥ 4) in the interval of night-dawn hours on a background of Pi 1 B and Pi 1 C, and can be accompaniedby auroral pulsations in this frequency range. Main spatial-temporal characteristics of the high-frequency geomagnetic pulsations are presented and their possible sources are discussed.

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In this paper, the properties of Pc1-2 and IPDP geomagnetic pulsations in the evening sector using the Yakut chain data and satellite measurements are described. It is shown that maximum intensity of Pc 1-2 type geomagnetic pulsations is observed at latitudes of peak precipitating proton fluxes and the pulsation amplitude is modulated with periods of 2-7 min. The large-scale undulations observed by the DMSP satellites on the equatorward diffuse auroral boundary, are formed during motion of the pulsation excitation region and a centre of the eastward electrojet to lower latitudes and during a growth of Pc 1-2 pulsation frequency. The oscillation periods of the undulation boundary are in agreement with modulation periods of Pc 1-2 amplitude, taking into account the observed wavelengths and assuming that the azimuthal velocity of their propagation is about 1-2 km/s. The results are interpreted in terms of the mechanism of spatial modulation of magnetically drifting and precipitating auroral protons.

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Recent studies of ULF pulsations in the inner magnetosphere (L < 6.6) with the Active Magnetospheric Particle Tracer Explorers Charge Composition Explorer are reviewed. Pulsations in the Pc 3-4 and Pi 2 bands with distinctive waveform, polarization, and spatial amplitude distribution are discussed separately. Specific pulsation types include toroidal-mode Pc 3-4 oscillations, equatorial compressional Pc 3 pulsations, Pi 2 pulsations, and giant pulsations. In addition to the highlights of published results, unresolved problems for each pulsation type are described.

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Conical distribution of both light and heavy ions are commonly observed in the magnetospheric plasma at various altitudes above the auroral regions and in the cusp/cleft region. The occurrence of these “conics” is shown to be well correlated with the presence of low frequency magnetosonic waves having frequencies close to the gyrofrequency of the heated ions. Dynamical spectra recorded onboard the AUREOL 3 satellite during the simultaneous occurrence of these waves and the generation of H⁺ conics have shown that, in such a case, resonant wave absorption at the gyrofrequency of the protons is likely to occur. These phenomena are due to the propagation, reflection and subsequent conversion of the magnetosonic waves throughout the inhomogeneous magnetospheric plasma. Theory allows to determine the energy budget of the resonant absorption and to describe some features of the observed spectra. Following similar ideas it is also possible to build up a theoretical scenario aiming at explaining the transverse heating of O⁺ ions and the formation of oxygen conics. As described in the experimental literature, this likely occurs far above the topside ionosphere and thus at higher altitudes than covered by the AUREOL 3 spacecraft.

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Enhanced magnetic field fluctuations observed during an ISEE-2 crossing of the plasma sheet boundary layer at X_GSE = 18.2 Re have the characteristics of electromagnetic ion cyclotron waves. The observed fluctuations propagate essentially along the magnetic field and are left-hand circularly polarized in the spacecraft frame, with frequencies below the proton cyclotron frequency (Ω_p) and peak power at about 0.2Ω_p. Plasma data indicate that these waves are associated with decreasing plasma β and occur in the presence of an anisotropic earthward directed proton beam with velocity less than the local Alfven speed. Linear Vlasov theory indicates that these waves are most likely excited by the electromagnetic ion cyclotron instability driven by the temperature anisotropy of the proton beam.

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A kinetic-MHD field-aligned eigenmode stability analysis of low frequency ballooning-mirror instabilities has been performed for anisotropic pressure plasmas in the magnetosphere. The ballooning mode is mainly a transverse wave driven unstable by pressure gradient in the bad curvature region. The mirror mode with a dominant compressional magnetic field perturbation is excited when the product of plasma beta and pressure anisotropy (P_⊥/P_|| > 1) is large. In the limit that the wave frequency is smaller than the energetic trapped particle magnetic drift frequency, which is usually much smaller than the energetic trapped particle bounce frequency, the energetic trapped particles experience the bounce-averaged wave structure due to their rapid bounce motion. For modes with north-south symmetric field-aligned structure of parallel perturbed magnetic field the energetic trapped particle kinetic pressure response is finite and cancels with their fluid pressure response so that the symmetric mode is stable. Physically the energetic trapped particles precess very rapidly across the B field, and their motion becomes very rigid with respect to low frequency symmetric MHD perturbations. For antisymmetric modes the energetic trapped particle kinetic pressure response from the northern hemisphere cancels with that from the southern hemisphere in a bounce period, and the instability β threshold of the antisymmetric mode is determined by the energetic particle fluid free energy. Pressure anisotropy with P_⊥/P_|| > 1 reduces the β_|| threshold. The antisymmetric mode changes from a ballooning mode with dominant transverse magnetic field components at P_⊥/P_|| = 1 to a hybrid ballooning-mirror type mode with comparable transverse and compressional magnetic field components near the equator as P_⊥/P_|| increases. With large equatorial plasma beta (β_|| ≥ Ο(1)) and pressure anisotropy (P_⊥/P_|| > 1) the field-aligned wave structure of antisymmetric ballooning-mirror mode resembles the multisatellite observations of a long lasting compressional Pc 5 wave event during November 14-15, 1979 (Takahashi et al., 1987). From the AMPTE/ CCE particle and magnetic field data observed during Pc 4-5 wave events we compute the ballooning-mirror instability parameters and perform a correlation study with the theoretical instability threshold. We find that compressional Pc 5 waves approximately satisfy the ballooning-mirror instability condition, and transverse Pc 4-5 waves are probably related to resonant ballooning instabilities with small pressure anisotropy.

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Oscillating phase shifts are frequently observed in ionospherically propagated HF radio waves in association with ULF geomagnetic pulsations. These Ionospheric Signatures of Pulsations (ISP) are observed in ionospherically reflected radio waves transmitted from ground stations, in radio signals transmitted from satellites to ground stations, and in the backscattered signals received by HF over-the-horizon radars. We review the techniques used to model the relationship between ISPs and geomagnetic pulsations. Model results for a variety of geophysical conditions are compared with observations.

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