Magnetohydrodynamic fluctuations in the Earth's magnetosheath at 1500 LT: ISEE 1 and ISEE 2
- Imperial College, London (England)
In the first study to employ dual-spacecraft cross-spectral techniques in the magnetosheath, the authors have analyzed ISEE 1 and ISEE 2 magnetic field and plasma data from an afternoon magnetosheath crossing to determine dominant MHD wave modes and directions. The principal discovery is of guided MHD waves traveling along the flow-modified wave characteristics. Wave polarizations were determined by transforming the magnetic field to a field- and boundary-aligned coordinate system. They have inferred wave propagation directions using the time delays between the passage of coherent structures across the spacecraft. Weaker broadband coherent oscillations in the direction radial from the planet could be associated with large scale motions of the shock and/or magnetopause, but the dominant signals appear not to be from such a source. Separate broadland Alfven and slow magnetoacoustic waves have been identified in the inner sheath, propagating across the field and flow toward the magnetopause. In the outer magnetosheath the most prominent disturbances were narrow-band Alfven waves propagating downstream and along the field. The phase propagation directions detected for the largest amplitude signals were closely aligned with the flow-modified wave characteristics, the group propagation directions. From this result, they infer that the sources of the dominant wave activity are localized MHD disturbances on the bow shock and not spatially coherent distributed sources such as bulk boundary motion. They suggest that the flow-modified characteristics of the two field-guided MHD modes may play an important role within the magnetosheath, determining the directions along which energy is transmitted between the solar wind and the magnetosphere.
- OSTI ID:
- 5187923
- Journal Information:
- Journal of Geophysical Research; (United States), Vol. 96:A1; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
MAGNETOSHEATH
HYDROMAGNETIC WAVES
ALFVEN WAVES
DATA ANALYSIS
EARTH MAGNETOSPHERE
ENERGY TRANSFER
INTERACTIONS
MAGNETOACOUSTIC WAVES
POLARIZATION
SOLAR WIND
TIME DELAY
WAVE PROPAGATION
EARTH ATMOSPHERE
SOLAR ACTIVITY
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena