Observations of electric fields associated with internal gravity waves

Abstract

At the Jicamarca Radio Observatory, the vertical drift component yields a very accurate measure of the eastward electric field. Occasionally, this drift component displays a downward phase progression, evidence for a relationship to a gravity wave. We examined the Jicamarca database for events of this type and made an attempt to determine the properties of the associated waves. The only measurables we have are the amplitudes, the frequency in the Earth‐fixed frame, and the vertical wavelength. 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, we then determine the frequency in the wind frame by solving the dispersion relation for gravity waves and the Doppler‐shift equation simultaneously. Typical values for the horizontal wavelength, vertical wavelength, and period in the wind frame are 600 km, 350 km, and 25 min, respectively. The typical gravity wave‐induced vertical drift perpendicular to B in these events is a few meters per second. This is marginal at best for seeding the Rayleigh‐Taylor instability. However, larger‐amplitude events may be masked by the development of the plumes themselves. All but two events found thus far occurred at night but the daytime cases are fascinating since the E region is expected to short out such fields.