Observations of Electric Fields Associated With Internal Gravity Waves

Details Observations of Electric Fields Associated With Internal Gravity Waves Observations of Electric Fields Associated With Internal Gravity Waves

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsa24a..04v&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #SA24A-04

Physics

2415 Equatorial Ionosphere, 2439 Ionospheric Irregularities, 3384 Acoustic-Gravity Waves

Scientific paper

Measurements of the ion drift perpendicular to the magnetic field allow an unambiguous determination of the electric field in that plane. At the Jicamarca Radio Observatory the vertical drift component yields a very accurate measure of the eastward electric field since the spectrum of the ISR signal is extremely narrow in the plane perpendicular to B. Occasionally this drift component displays a downward-phase progression, which is evidence for a relationship to a gravity wave. The idea that gravity waves can create electric fields has been around for awhile but there are only two cases reported in the literature, one being from the same data set discussed here. We examined the Jicamarca database for events of this type and made an attempt to determine the properties of the associated waves. The only measureables we have are the frequency in the earth-fixed frame and the vertical wavelength. We extend the information as follows. In order to avoid shorting by the current along magnetic field lines, we argue that the propagation must be close to pure zonal. We then use measurements or models of the zonal plasma drift and argue that the zonal wind should be in the same direction and about 15% higher. Using this estimate, along with temperature and density estimates from the MSIS computer model, we then solve the dispersion relation for gravity waves and the Doppler-shift equation simultaneously. This allows us to determine the frequency in the wind frame. A typical value for the horizontal wavelength, vertical wavelength, and period in the wind frame is 600 km, 350 km, and 25 minutes, respectively. All but one event found thus far occurred at night but the daytime case is fascinating since the E region is expected to short out such fields. The typical gravity wave-induced vertical drift perpendicular to B in these events is a few m/s. This is sufficient to seed the Rayleigh-Taylor instability.

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