The structure of localized nighttime auroral zone scintillation enhancements

Abstract

Simultaneous observations of the polar-orbiting Wideband satellite at two auroral zone stations (separated by approximately 200 km along the geomagnetic meridian) were made during November 1977. The latitudinal distribution of the average scintillation occurrence at each station shows a local maximum at the point where the propagation vector lies within an L shell. This supports the hypothesis that the enhancement is a geometrical effect due to L shell aligned, sheetlike irregularities. The detailed structure of the average scintillation occurrence as well as the scintillation patterns on individual passes shows, however, that the source regions are confined in latitude. From a detailed analysis of total electron content data we were able to show that the local scintillation enhancements occur in a region of enhanced F region ionization with a steep gradient at its equatorward edge. The source region lies within the general confines of the diffuse aurora, often with too limited a latitudinal extent to cause an enhancement at both stations. These new results are discussed in light of recent theoretical analysis by Ossakow and Chaturvedi that shows that the current convective instability, which is essentially a stable E x B configuration destabilized by moderate field-aligned currents, can explain the irregularities. The sheetlike structure is a result of the nonlinear saturation of the instability. The linearly unstable mode, which would give rise to meridional structures, is nonlinearly damped while the dominant nonlinearity favors the perpendicular modes that cause the sheetlike structures.

Climatology of GPS phase scintillation at northern high latitudes for the period from 2008 to 2013

“…Ionospheric scintillation is thought to be caused by irregularities of scale sizes from a few hundred meters to a kilometer, which are less elongated (Fremouw et al, 1985;Wernik et al, 1990) than small-scale irregularities, showing anisotropy characterized by a range of axial ratios (Rino and Owen, 1980;Livingston et al, 1982;Gola et al, 1992) and various shapes from cylindrical to sheet-like, as discussed by these authors and briefly summarized previously (see, e.g., Prikryl et al, 2011). Assuming an IPP height of 350 km, Gola et al (1992) generated maps of amplitude scintillation as a function of angles between the ray path and the geomagnetic L-shell and the plane of magnetic meridian indicating a predominance of field-aligned irregularities.…”

Optimum detrending of raw GPS data for scintillation measurements at auroral latitudes

“…Those events were just named ''phase without amplitude'' scintillation events. During experiments successive to wideband and dealing with polar orbiting satellites in particular, it was observed that the average nighttime auroral zone scintillation activity can exhibit a localized enhancement when the propagation vector lies within an L-shell (Rino and Matthews, 1980;Rino and Owen, 1980). Such an enhancement is explained on the basis of the weak scattering approximation, where scintillation indices are controlled by a geometrical factor, taking into account irregularity shape and their orientation with respect to the magnetic field.…”

Climatology of GPS phase scintillation and HF radar backscatter for the high-latitude ionosphere under solar minimum conditions

“…However, the anisotropy is size-dependent and larger irregularities are less elongated than smaller ones (Fremouw et al, 1985;Wernik et al, 1990). VHF and UHF scintillation measurements at high latitudes (Rino and Owen, 1980;Livingston et al, 1982;Gola et al, 1992) suggested a range of axial ratios to characterize irregularity shapes. The elongated and closely field-aligned cylindrical irregularities and shorter elongated rod-like irregularities have one axis of symmetry described by axial ratio a:1:1.…”