Ballooning mode waves prior to substorm-associated dipolarizations: Geotail observations

Details Ballooning mode waves prior to substorm-associated dipolarizations: Geotail observations Ballooning mode waves prior to substorm-associated dipolarizations: Geotail observations

Apr 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008georl..3507103s&link_type=abstract

Geophysical Research Letters, Volume 35, Issue 7, CiteID L07103

Physics

Geophysics

31

Magnetospheric Physics: Mhd Waves And Instabilities (2149, 6050, 7836), Magnetospheric Physics: Substorms, Magnetospheric Physics: Auroral Phenomena (2407), Magnetospheric Physics: Magnetotail, Mathematical Geophysics: Wavelet Transform (3255, 4455)

Scientific paper

We present in situ observations consistent with the ballooning mode in the vicinity of the magnetic equator at X GSM = -10 to -13 R E prior to substorm-associated dipolarization onsets. The ballooning instability is expected to have a wavevector along the Y direction and to give variation to the curvature of the ambient magnetic field lines. The magnetic field fluctuations appearing in the B x component are transported by the ambient plasma drift in the Y direction. A discrete frequency band would be identified in time series data if the mode has a discrete wavelength. The ballooning mode of this property was identified at the magnetic equator a few min before dipolarization onsets only when the plasma β was large (20 to 70). Using low-energy ion velocity data, we show that the mode has almost zero frequency in the plasma rest frame so that ω sc ~ k y . v y , where ω sc is the frequency in the spacecraft frame, and k y and v y are the wavenumber and the ambient plasma flow in the Y direction, respectively. This enables us to estimate the wavelengths of the ballooning mode, which were found to be of the order of the ion Larmor radius.

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