Auroral E and F Layer Ionospheric Irregularities Sensed by a Kilometer-Spaced GNSS Receiver Array

Abstract

This paper surveys GPS L1 and L2C scintillations automatically detected, classified, and attributed to a scattering layer from data collected in 2014-2015 by the Scintillation Auroral GPS Array (SAGA) in Poker Flat Research Range, Alaska. The automated method scans scintillation indices recorded by SAGA for array-wide intervals of phase scintillation, amplitude scintillation, or both phase-and-amplitude scintillation at each of L1 and L2 frequencies. For each of the scintillating time intervals found, plasma density data from the collocated Poker Flat Incoherent Scatter Radar (PFISR) are used to attribute the GPS signal scattering to either the E layer or the F layer of the ionosphere, based on whether the peak density is above or below 200 km altitude. The vast majority of scintillation events are phase scintillations, whether at L1 or at L2C. While the majority of them are attributed to the F layer in 2014, the majority of the scintillation events in 2015 are attributed to the E layer, based on the PFISR data. This indicates that E-layer-related scintillation may be quite common at auroral latitudes, and that GPS receivers are sensitive to the irregularities occurring there. We follow the survey with an individual case study of an L1 phase scintillation event associated with the E region. Analysis of 100 Hz detrended and filter power and phase from SAGA show that the phase variations have no time lag across the array, indicating that the irregularities’ drift velocity, anisotropy, scattering layer height and thickness cannot be estimated directly from SAGA for this event. However, the Satellite-beacon Ionospheric-scintillation Global Model of the upper Atmosphere (SIGMA) forward propagation scintillation model is used to search for the parameters that best fit the observed power spectral density (PSD) of the scintillations. A best fit model of a scattering layer in the E region at 120 km in the region shows a reasonable agreement with the observed PSD. Interestingly an F layer irregularity model at 350 km produces a slightly better fit. The PFISR density data show enhanced densities from the E layer through the lower F layer during this time. Further investigation of this event and comparisons to other E layer and F layer events will help resolve this discrepancy in the future.