Scattering of radio waves by the F‐region of the ionosphere

Abstract

Records are reproduced showing diffuse echoes from the F‐region of the ionosphere received continuously at night in equatorial regions over a wide range of wave‐frequency. Tney are interpreted as due to Rayleigh scattering by spatial irregularities in the distribution of electron‐density at or above a definite level in the F‐region. Because of the highly dispersive nature of the ionosphere, there is no marked dependence of Rayleigh scattering upon wave‐frequency such as there is for a non‐dispersive medium. According to this interpretation, variation of the maximum wave‐frequency to which diffuse echoes can be followed has nothing to do with variation of the maximum electron‐density of an ionospheric region, but merely indicates variation in the size of irregularities in electron‐density. Scattering of this type may have some bearing upon the phenomenon of persistence of E‐region echoes to wave‐frequencies greater than the critical penetration‐frequency of the E‐region.

Electrodynamics of midlatitude spread F: 1. Observations of unstable, gravity wave‐induced ionospheric electric fields at tropical latitudes

“…The phenomenon of spread F has intrigued observers of the midlatitude ionosphere since the earliest days of experimental ionospheric research [Berkner and Wells, 1934;Booker and Wells, 1938]. Until the 1960s, most observers believed that plasma instabilities were responsible for spread F, but since then the focus of research has shifted toward disturbances produced by attoospheric gravity waves (see Bowman [1990] for a recent review).…”

Backscatter measurements of 11‐cm equatorial spread‐F irregularities

“…Radar backscatter has been used to study equatorial spread-F irregularities for more than four decades, first in the form of vertical-incidence ionosondes [Booker and Wells, 1938] and highfrequency (HF) backscatter radars [Clemesha, 1964;Kelleher and Skinner, 19711, and most recently in the form of high-power backscatter radars that operate in the very-high-frequency (VHF) and ultra-highfrequency (UHF) bands [Farley et al, 1970;Woodman and La Hoz, 1976;Tsunoda et al, 1979;Towle, 19801. A characteristic trend apparent in these measurements is the use of increasingly higher transmitter power at higher radar frequencies.…”

Images of transequatorial F region bubbles in 630‐ and 777‐nm emissions compared with satellite measurements

“…All of the observations discussed above showed plasma structures which drifted to the east for most of each night and which have the form of field-aligned bubbles of lowdensity plasma of scale size of tens to hundreds of kilometers extending across the equator. These have been observed by satellite [e.g., McClure et al, 1977] and give rise to the spread F phenomenon of radio reflections from irregularities in the meter-to-kilometer ionosonde wavelengths [Booker and Wells, 1938] and plumes of strong radar backscatter echoes from irregularities with meter spatial scales [Woodman and La Hoz, 1976].…”