Analysis of Cluster Observations of Low Frequency Electric and Magnetic Field Fluctuations In a High Speed Flow Associated with Current Sheet Crossings in the Geomagnetic Tail

Details Analysis of Cluster Observations of Low Frequency Electric and Magnetic Field Fluctuations In a High Speed Flow Associated with Current Sheet Crossings in the Geomagnetic Tail Analysis of Cluster Observations of Low Frequency Electric and Magnetic Field Fluctuations In a High Speed Flow Associated with Current Sheet Crossings in the Geomagnetic Tail

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm33b0361d&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SM33B-0361

Physics

2723 Magnetic Reconnection (7526, 7835), 2744 Magnetotail, 2764 Plasma Sheet, 2790 Substorms

Scientific paper

In this paper, we present a study, using electric and magnetic field measurements from the four Cluster spacecraft, of the scale size, phase velocity, coherence length, power spectra, Poynting flux spectrum, and wave normal directions, and the E/B ratio observed over the spacecraft frequency range from 0.1 Hz to 10 Hz during several current sheet crossings associated with high speed Earthward flow in the geomagnetic tail on August 17, 2003 at about 17:00 UT. The Cluster spacecraft array was located near 18 Re geocentric distance and 1.2 MLT near the equatorial plane. The spacecraft separation was about 300 km. The high speed H+ flow velocity was about 800-900 km/s and oriented at ~130 degrees relative to the magnetic field. Using phase lag analysis of the wave spectra measurement between the four Cluster spacecraft, it was found that the wave propagated nearly in the equatorial plane, normal to the magnetic field with a phase velocity of about 700-800 km/s relative to the Earth. Distribution functions from the CIS CODIF detectors showed highly structured H+ and O+ distribution functions with gyrating beams and shell-like distributions. In the rest frame of the H+ flow, the propagation velocity of the waves was on the order of ~100 km/s and much less than the H+ Alfven velocity (~1000km/s). The H+ rest frame frequency of these waves was comparable to or less than the Hydrogen cyclotron frequency. In general, he perpendicular scale sizes of the waves varied from 700 km to above 30,000 km. These waves carry dynamically significant Poynting flux over scale in-situ sizes ranging from 3000 km to 30,000 km capable of driving intense aurora over ionospheric scales of 100 km to 1000 km. At smaller scales (<100 km), the waves have large amplitude electric field fluctuations (~100 mV/m), a high E/B ratio characteristic and the coherence spectra between different spacecraft goes to zero. We will compare simultaneous measurements of the waves and ion distribution functions in a discussion of possible free energy sources.

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