Whistler mode wave packets in the Earth's foreshock region
Abstract
The definite identification of the basic modes of the variety of electromagnetic waves common in the interplanetary medium upstream of the Earth's bow shock has been difficult because of the Doppler shifting which results from their attempts to propagate in the supersonic solar wind. We have used magnetometer data from the dual ISEE-1 and -2 spacecraft, taken when the spacecraft were separated by a few hundred kilometres, to measure the apparent velocities of a subset of these waves. This has allowed the first determination of wave phase velocities, rest-frame frequencies, wavelengths, intrinsic polarizations and thus wave modes. We have now applied this technique to the class of upstream phenomena designated the discrete wave packets. These are isolated fairly monochromatic wave packets with frequencies ~0.4 Hz in the spacecraft frame which rotate in the left-handed sense about the magnetic field direction as observed in the spacecraft frame. Our studies of the time delay between the observation of such wave packets at the two spacecraft demonstrate conclusively that in the plasma rest frame these waves are, in fact, right-handed polarized waves with frequencies several times greater than the proton gyro-frequency, attempting to propagate upstream against the solar wind, but being carried towards the Earth by the solar wind flow.
- Publication:
-
Nature
- Pub Date:
- October 1980
- DOI:
- 10.1038/287417a0
- Bibcode:
- 1980Natur.287..417H
- Keywords:
-
- Bow Waves;
- Interplanetary Medium;
- Shock Wave Propagation;
- Whistlers;
- Earth Surface;
- Polarized Electromagnetic Radiation;
- Propagation Modes;
- Satellite Observation;
- Velocity Measurement;
- Geophysics