Aerodynamical Mechanisms Producing Electronic Density Fluctuations in Turbulent Ionized Layers

Abstract

Various radio effects of the turbulence in the low ionosphere are discussed with a view toward determining the order of magnitude of the turbulence parameters in this region. These effects include vhf scattering, sporadic E-layer phenomena, and diffraction patterns in reflection. The required electron density fluctuations (ΔN/N)² fluctuate around 10^-4 and the scale of the turbulence I is roughly 100 to 200 meters. The latter quantity measured directly in the troposphere is of about the same order of magnitude. The underlying purpose of the paper is to study the aerodynamical mechanisms of turbulence. Pressure fluctuations result from the "collisions and extensions between turbulent eddies" in a uniform gas, or from vertical transport in the atmosphere with its varying pressure. It is shown that such pressure fluctuations are too small, by a factor of about 10^-4, to produce the observed density fluctuations. However, the vertical transport mechanism produces two other effects which are independent of the energy of the turbulence and are of the right order of intensity. First, in a nonadiabatic atmosphere the vertical transport of air masses produces fluctuations of temperature. These, in turn, give rise to air density fluctuations, and proportional electron density fluctuations. Second, fluctuations of electron density result directly from transport in the presence of a gradient of electron density. These two effects, for the same uniform turbulence, occur at different levels in an ionospheric layer. They are sufficient to explain the stratification properties of sporadic E.