Spectral behavior of phase scintillation in the nighttime auroral region

Abstract

Enhancement of phase and intensity scintillation, as a radio line of sight scans through grazing incidence on the local L shell in the nightside diffuse-auroral ionosphere, has been well documented by means of data from the DNA Wideband satellite. In this paper we describe systematic behavior of the phase spectrum found in the enhancement region over Poker Flat, Alaska. Routine Wideband processing included spectral analysis of 20-s (•,, 60-km) segments of VHF and UHF phase records and log linear fits thereto. Tabulation of the resulting power law spectral indices, p, disclosed increased values in the scintillation enhancement region. It has been established that the increase in p is the signature of a physically real phenomenon and not merely an artifact of statistical nonstationarity arising from the narrowness of the scintillation strength enhancement. Moreover, it has been found that p is not increased in strength enhancements occurring close to the magnetic zenith. Indeed, in some cases, it is substantially decreased. A possible source of these unexpected spectral behaviors is size-dependent anisotropy, an idealization of the irregularities responsible being small-scale field-aligned rods imbedded in large-scale shell-aligned sheets. We also present examples of multiple-regime power law spectra, characterized by an increased spectral index at short structure wavelengths (less than a few hundred meters north-south) and, more frequently, by an increased index at large wavelengths (more than a few kilometers). These spectral breaks occur both separately and together and both within and outside the scintillation enhancement region.

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

“…The occurrence of amplitude and phase scintillation Published by Copernicus Publications on behalf of the European Geosciences Union. was found to be particularly elevated on the dayside in the cusp/cleft region, showing variations with season and magnetic activity (Kersley et al, 1988(Kersley et al, , 1995MacDougall, 1990a, b;Gola et al, 1992). In the polar cap, amplitude scintillation exhibited clear seasonal and UT variation, which was consistent with mesoscale plasma density modeling results (Basu et al, 1995;Sojka et al, 1994).…”

“…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.…”

“…Sheet-like (a:a:1) and non-symmetrical wing-like (a:b:1, where a > b) structures are elongated along surfaces of constant magnetic latitude (L-shells). The values of a are typically between 3 and 15 and b < 3 (Livingston et al, 1982;Gola et al, 1992). Gola et al (1992) showed maps of an amplitude scintillation index as a function of angles between the ray path and the geomagnetic L-shell and the plane of magnetic meridian at an altitude of 350 km indicating a predominance of field-aligned irregularities.…”

“…The dependence of total electron content (TEC) and scintillation intensity on these factors has been recognized and studied at VHF/UHF frequencies for many years (Aarons, 1982;Basu et al, 1987;Kersley et al, 1988;Gola et al, 1992). More recently, GPS receivers have improved coverage at high latitudes (Aarons, 1997;Aarons et al, 2000;Mitchell et al, 2005;Alfonsi et al, 2008;Jayachandran et al, 2009;Spogli et al, 2009;Yin et al, 2009;Li et al, 2010).…”

Irregular structures of the F layer at high latitudes during ionospheric heating

“…This e ect can be due to increased e ciency of heating. The observed values are of the same order of magnitude as the integrated intensities of natural irregularities predicted by the WBMOD model (Fremouw et al, 1985).…”