Scale sizes and lifetimes of F region plasma cloud striations as determined by the condition of marginal stability

Abstract

The two‐dimensional integrated Pedersen conductivity model for F region plasma cloud striation development may be cast in dimensionless form. The result implies that a structure's stability against bifurcation depends upon whether a diffusion parameter R exceeds a critical value. The critical R for striations is determined by high resolution computer simulation for conductivity ratios M from 2 to 30. Our results combined with electron diffusivity of order 1 m²/s agree with observed minimum scale sizes of 15 m. For turbulent diffusivity of order 100 m²/s, our results agree with frequent observations of kilometer scale structures which ‘freeze up’ and last for times of order 104 s. This lifetime is also predicted by our results.

Nonlinear equatorial spread F: The effect of neutral winds and background Pedersen conductivity

“…If we note that an equatorial spread F plume (bubble) is nothing more than an inverse plasma cloud "finger" (i.e., an elongated region of low density plasma (an ESF "plume") penetrating a region of high density plasma is the inverse of an elongated region of high density plasma (a plasma cloud "finger") penetrating a region of low density plasma), we find that the question of why the 2LE plume bifurcated and the 2L plume did not has already been answered for us. McDonald et al, [1981] have shown in their study of bifurcation tendencies of plasma cloud fingers that the critical quantity determining the speed with which a plasma finger will bifurcate is M, the ratio of the Pedersen conductivities inside and outside the finger.…”

“…Almost as striking is the fact that the 2LE plume bifurcated while the 2L plume did not. The inevitability of the bifurcation in calculation 2LE can be seen even in the very early time plot at 1500 sec, where the characteristic flattening of a significant number of contours in the upper portion of the plume, the sure signal of imminent bifurcation in barium cloud studies [Zabusky et al', 1973;Scannapieco et al, 1974;Ossakow et al, 1977;McDonald et al, 1980], can be seen. The close similarity of the physics of the ESF gravitational instability and that of the ExB gradient drift instability associated with the bifurcation and striation process in plasma clouds, has been noted by .…”

“…The close similarity of the physics of the ESF gravitational instability and that of the ExB gradient drift instability associated with the bifurcation and striation process in plasma clouds, has been noted by . We shall draw heavily on our knowledge of bifurcation tendencies in plasma clouds Iossakow et al, 1977;McDonald et al, 1980] when we address the question of why the plume in calculation 2LE bifurcated while that in calculation 2L did not, later in this paper.…”

A review on the numerical simulation of equatorial plasma bubbles toward scintillation evaluation and forecasting

“…2. From previous plasma cloud experiments (e.g., McDonald et al 1981), they concluded that a background E-region Pedersen conductivity played a role in the bifurcation of EPBs. They also found that a uniform eastward neutral wind contributed to the westward tilt of the EPBs, as shown Fig.…”

Neutral Flow through Ion Clouds.

“…Further evidence for this suggestion is that the size of the eddies in the neutral flow roughly corresponds to the sizes of the ion cloud structures observed. The neutral turbulence structuring mechanism offers an alternative to the mechanism discussed by McDonald et al (1981) Table 1.…”