Analysis of spectral and propagation characteristics of ionospheric structures over Poker Flat Research Range using modelling and observations.

Ionospheric scintillations are the fluctuations in satellite signal phase and amplitude caused by the irregularities in the electron density that affects satellite-based systems. Characterization of the ionospheric irregularities helps us to analyze the scintillation effects on a various number of modern-day satellite-based applications. The three-dimensional (3-D) global electromagnetic (EM) wave propagation model "Satellite-beacon Ionospheric scintillation Global Model of the upper Atmosphere" (SIGMA), that simulates the signal propagated from a moving satellite to the ground passing through multiple phase screens (MPS), is used to characterize the ionospheric irregularity structures. In this study, we analyze the similarities/differences of spectral and propagation characteristics of ionospheric irregularities at E and F region heights. The propagation and spectral effects are based on the description of plasma density irregularities in the model with input parameters such as axial ratio, spectral index, outer scale, height and thickness of the irregularity layer, the electron number density and the plasma drift velocity. The initial estimates of SIGMA propagation parameters such as number density are derived from the Poker Flat Incoherent Scatter Radar (PFISR), the drift speed and its direction are obtained from the Scintillation Auroral GPS Array (SAGA), located at Poker Flat Research Range (PFRR), Alaska. The model outputs the simulated signal phase and power time series, which is then compared with the Global Positioning System (GPS) observations from SAGA. The power spectral density (PSD) derived from the signal phase is used to find the SIGMA optimal inputs for the best-simulated PSD fit to the observed PSD. The E-region substorm event on 16 November 2014 at 09:13 UT, and two F region events on 7 October 2015 at 18:07 UT and 16 November 2014 at 01:17 UT resp., which are geomagnetically active days with the availability of coexisting auxiliary observations and scintillation measurements, are selected for this study. The spectral analysis using two different spectral models called Hybrid and Shkarofsky, reveals that the E region irregularities are more elongated along the magnetic field lines with rod-shaped irregularity structures. In contrast, the F region irregularities are found to have wing/sheet-like structures with irregularities extending both along and across the field lines. The spectral index that depends on the size of irregularities and the level of scintillation activity shows a lesser spectral index for E region event than F region events. It also reveals that the spectral index decreases with the strength of phase fluctuations. Furthermore, the propagation parameters obtained by SIGMA are found to agree well with the PFISR and SAGA observations for all three cases. Thus, this study, using the propagation model, helps us understand the characteristic structures of the E and F region ionosphere.