The fast magnetosonic waves in the frequency range 1–11 Hz (i.e., above the proton gyrofrequency Ωp) are considered. The electric wave field δE (mostly less than 0.5 mV/m) has an elliptic polarization in the plane perpendicular to B. While the magnetic wave field δB is strictly polarized along the ambient magnetic field, the ellipticity and the sense of rotation of the electric field polarization ellipses are crucial parameters for the identification of the wave mode. The waves are right‐hand polarized, and the ellipticity is usually about 0.2. The main axis of the ellipse is close to the azimuthal direction. The wave vector k is almost parallel to δE, and thus the fast magnetosonic waves propagate at small angles to the azimuthal direction. The wavelengths are usually between 150 and 300 km. The δE/δB ratio of the waves is between νA and υA(1 + ω²/Ωp²)1/2, where υA is the Alfvén velocity. In one case a burst of pure electrostatic modes near the second harmonic of the proton gyrofrequency was observed.

One hundred eighty‐six days of electric field data from the GEOS 2 electron beam experiment have been used to study magnetospheric fluctuations at geostationary orbit with periods between 150 and 600 s. While fluctuations are nearly always present in the electric field data from the dayside magnetosphere with typical amplitudes between 0.2 and 0.5 mV/m, it is often hard to find well‐defined concurrent pulsations in the GEOS 2 magnetic field data. Most events occur near noon and have the same characteristics: They are toroidal and nearly linearly polarized, the sense of polarization and the orientation angles of the polarization ellipses change sign near noon, the instantaneous frequency of the fluctuations is correlated with the instantaneous electron density, and in a given sector of the magnetosphere the sense of polarization depends on the frequency. There is strong evidence that these fluctuations are fundamental mode eigenoscillations of field lines in the vicinity of the spacecraft which are generated in the inhomogeneous plasma of the magnetosphere by some kind of solar wind‐driven surface waves at the magnetopause or at the low‐latitude boundary layer.

On March 6, 1979, long‐period hydromagnetic waves were excited in the forenoon magnetosphere by a sudden impulse (SI). The plasma drift velocity and magnetic field oscillations associated with these waves were observed by the electron gun experiment and the magnetometer, respectively, onboard the GEOS 2 satellite in the equatorial plane. The waves had both compressional and transverse components and had their probable source in a single, tailward traveling, large‐scale magnetopause surface “wavelet” (i.e., a single rarefaction/compression pulse) caused by the passage of an interplanetary shock front. This surface wavelet apparently coupled into the inner magnetosphere via the field line resonance mechanism. The satellite observations and the Poynting vectors calculated from these are consistent with a location of the resonance region earthward of GEOS 2 during the first 5 min after the SI while the satellite was located just inside the resonance region at later times. This shift in the relative location of the resonance region was probably caused by an increase of the Alfvén velocity as a result of the compression of the magnetosphere associated with the sudden impulse. The stronger‐than‐usual compressional magnetic field component most likely had its origin in the relatively larger wavelength of the SI‐excited surface wavelet (compared with that of Kelvin‐Helmholtz‐excited surface waves).

The spectral power and occurrence rate of long‐period magnetospheric pulsations (predominantly fundamental mode toroidal Pc 5) observed by the electron beam experiment on board GEOS 2 are compared with IMF and solar wind parameters. No clear influences of IMF orientation and magnitude on pulsation amplitudes and occurrence rate are found. Significant correlations, however, do exist between the spectral power of pulsations and the solar wind bulk velocity, and between the spectral power and the solar wind kinetic energy flux. The sign of the latter correlation depends on the Kp index. For Kp = 0 the pulsation power decreases with increasing solar wind kinetic energy flux, whereas it increases for Kp ≥ 1. Our results are consistent with the Kelvin‐Helmholtz instability at the inner side of the low‐latitude boundary layer being the dominant mechanism for the generation of fundamental mode toroidal Pc 5 magnetospheric pulsations. Flux transfer events play only an inferior role as energy sources for these pulsations. The coupling efficiency of surface waves at the boundary layer to shear Alfvén waves near geostationary orbit seems to change significantly if the geostationary orbit is inside the plasmasphere.

Electric and magnetic field data measured by the electron beam experiment and the magnetometer on board the geostationary satellite GEOS 2 were used to investigate wave Poynting vectors associated with long-period (150-600 s) magnetospheric pulsations. A total of 3580 vectors were calculated for pulsations occurring during 186 days in the dayside magnetosphere. The ratio between the electric and magnetic field wave amplitudes was in genera ! well above the local Alfv6n speed and was found to increase with increasing wave frequency. The fraction of electric field pulsations for which magnetic wave components could also be identified was therefore larger for the low-and smaller for the high-frequency events in the range 1.67-6.67 mHz. Poynting fluxes were found to have values between 10 -xø and 10 -5 W/m 2. For most pulsations with periods between 400 and 600 s the part of the vectors perpendicular to the ambient magnetic field had an inward component and was directed toward the nose of the magnetosphere in the prenoon and afternoon sectors. The behavior of the corresponding components of the pulsations with a 150-to 300-s period was not as clear. For all events observed in the winter season (between November 1, 1978, and February 28, 1979), 59% of the vectors had a field-aligned component directed into the northern hemisphere, whereas 41% of the vectors were directed southward. The frequency dependence of the E/B ratio, the magnitudes of the Poynting vectors, and their directional distributions are consistent for most events with the picture of standing shear Alfv6n waves caused by solar wind driven surface waves on the outer boundaries of the magnetosphere.