This project is devoted to the multi-disciplinary study of a particular class of ULF waves in the near-Earth space: medium-scale Alfven waves (with azimuthal wave numbers m>>1). Their spatial structure is mainly determined by MHD effects, but due to large azimuthal electric field component the high-m waves resonantly interact with energetic particles. The proposed project comprises complementary and interrelated theoretical and experimental tasks. Adequate theoretical description of medium-scale Alfven waves demands a hybrid approach, where kinetic effects are included in MHD equations. We are going to elaborate the theory of a new ULF phenomenon - the Alfvenic waveguide, where the wave energy is trapped between the conjugate ionospheres and cut-off shells, and is channeled along azimuth. A new two-step conception of the Alfven wave generation will be elaborated: (1) non-steady current of drifting energetic particles generates in a non-resonant way broadband supra-thermal hydromagnetic fluctuations; (2) a resonant instability provides amplification of narrow-band waves from these turbulent "embryos". This conception will be applied to the interpretation of ULF wave excitation during magnetic storms. We intend to develop a unified gyro-kinetic theory describing both transverse spatial structure and growth rate of coupled Alfven and compressional modes taking into account the plasma density inhomogeneity across magnetic shells and along field lines, finite anisotropic pressure, and resonant drift-bounce wave-particle interaction. Combined data from multi-satellite CLUSTER magnetic, electric, and particle sensors, ionospheric radars, and ground magnetometer array will be analyzed to elucidate the spatio-temporal structure of medium-scale waves and compare it with the elaborated theoretical models. This project will enrich the physics of nighttime ULF waves and transients by developing a new analytical theory to characterize the interaction of Alfven waves with different types of resistive layers that may occur in the nightside magnetosphere: the auroral acceleration region; turbulent layers with anomalous conductivity; and thin current sheets with steep bending of magnetic field lines embedded in high-pressure plasma. This theory will promote the notion on the scale-dependent coupling between the magnetosphere and ionosphere. The spatial structure of intense electromagnetic bursts detected by CLUSTER on field lines conjugate to auroral arcs (as determined from ground auroral cameras) will be examined to verify the hypothesis that medium-scale Alfven waves provide energy to the auroral arc intensification. Coordinated multi-instrument analysis will be performed in search of localized transient response to an occurrence of anomalous resistivity on auroral field lines and of the magnetotail-related ionospheric ULF signatures. The project will provide first comprehensive review of meso-scale electromagnetic phenomena in the near-Earth environment.