High frequency drift waves with wavelengths below the ion gyroradius in equatorial spread F

Abstract

Evidence is given for intense VHF and UHF radar backscatter during equatorial Spread F resulting from irregularities of 1 meter and 36 cm, respectively. The linear theory for high frequency (ω ≳ Ωi, where Ωi is the ion gyrofrequency) drift waves, generated by the drift‐cyclotron and lower‐hybrid‐drift instabilities, is presented. This linear theory is set forth as a possible explanation for the occurrence of these irregularities below the ion gyroradius. The maximum growth for these instabilities occurs for kre ∼ 1, where k is the wavenumber perpendicular to the magnetic field and re is the electron gyroradius. For these instabilities, the growth rate is γ ≳ (me/mi)¼ Ωi and results in growth times less than a second. For typical equatorial Spread F ionospheric parameters, where (νii/Ωi) (kri)² ≳ 1 (νii is the ion‐ion collision frequency, rI is the ion gyroradius), the lower‐hybrid‐drift instability is dominant.

Backscatter measurements of 11‐cm equatorial spread‐F irregularities

“…The experiment utilizing both ALTAIR and TRADEX radars is described in Section III, and the preliminary results are presented in Section IV. In Section V, the results are discussed in relation to an existing plasma instability model that has been proposed as the source mechanism for these smallscale FAI that exist, with spatial wavelengths, below the ion gyroradius [Huba et al, 1978].…”

On 11‐cm irregularities during equatorial spread F

“…fluctuations exist with scale sizes of 3m, lm and 36 cm, respectively [Farley et al, 1970;Woodman and LaHoz, 1976;Costa and Kelley, 1978a,b;Huba et al, 1978). Most recently, Tsunoda (1980) has observed radar backscatter from 11 cm (1320 MHz) irregularities during equatorial spread F at high altitudes, using the TRADEX radar.…”

“…Based upon this evidence, it has been suggested that various drift instabilities are responsible for the short wavelength irregularities [Huba et al, 1978; Costa and Kelley, 1978a,b;Huba and Ossakow, 1979a,b], depending upon…”

A Review of Recent Results on Spread F Theory

“…where one has taken T e = = 0 for simplicity (see Ossakow et al, 1978), B = B~~ and the subscript o refers to equilibrium quantities.…”

“…1 m. Finally, from this instability , large growth rates Ci 6~L ) resulting in growth times, t = r~~~ less than a second can occur . For more details of this work see Huba et al (1978) .…”