A Configuration Space Model for Intermediate‐Scale Ionospheric Structure

Abstract

Stochastic ionospheric structure is characterized by spectral density functions (SDFs), which are formally the average intensity of Fourier transformations of the electron density structure. Structure elongation along magnetic field lines is typically accommodated by constraining contours of constant spatial correlation to field‐aligned ellipsoidal surfaces. Structure realizations are generated by imposing the square root of the SDF onto uncorrelated random Fourier modes. The approach has been used successfully for interpreting both in situ and remote propagation diagnostics. However, the only connection to the field‐aligned structures generated by the underlying instability mechanism is the correlation scale. This paper introduces a configuration space model that constructs realizations as summations of field‐aligned elemental striations with a prescribed scale and peak electron density. We show that by choosing the contributing scales according to a bifurcation rule and imposing a power law intensity scaling, the corresponding SDF closely approximates an inverse power law. Thus, configuration space realizations can be structured to reproduce prescribed or measured SDFs from one‐dimensional scans. Stochastic variation comes from an imposed random distribution of striation locations, which are defined by their intercept in a reference slice plane. To conform more directly to physics‐based simulations, the striations can be interpreted as voids in the background electron density. The model is designed to support propagation simulations with arbitrary propagation angles relative to the local magnetic field direction. Relations between in situ structure and diagnostic measurements as well as phase screen equivalence can be explored.

Wave Field Propagation in Extended Highly Anisotropic Media

“…The weighting only affects the result when the spectral intensity variation with κ z is resolved and confined to κ z =0. The prediction is verified in Figure 6 of Rino et al (). At the time that paper was written, no confirming calculations were available.…”

“…Following the development in Rino et al (), a configuration‐space realization of is constructed as a summation of physical striations. Formally, …”

“…The study is based on complex field simulations generated by split‐step integration of the parabolic wave equation (PWE). Structure realizations are constructed with a recently developed configuration‐space model described in Rino et al (). Configuration‐space realizations are summations of physical striations with size and intensity distributions constrained to follow two‐component inverse power law spectral density functions (SDFs).…”

On the Relationship Between the Rate of Change of Total Electron Content Index (ROTI), Irregularity Strength (CkL), and the Scintillation Index (S4)

“…This would not be surprising if the distribution of ionospheric structure along magnetic field lines is not stochastic, but instead varies in a deterministic fashion that is not well described by the Rino model. An alternative irregularity model, called the configuration space model, has been proposed recently in an effort to improve the description of field‐aligned variations and their effect on radio propagation (Rino et al, ). A third possibility is that the measured S 4 values themselves are inaccurate, since the statistics were computed over a temporal interval which is too large a fraction of the Fresnel time scale.…”

Generation of Realizations of Electron Density for Numerical Electromagnetic Propagation Simulations

“…Statistically based or random phase screens are usually generated using Fourier transform techniques where the phase of the screen is calculated as the FFT of the product of the square root of the desired power spectrum and white Gaussian noise. In related study, Rino et al (2019Rino et al ( , 2018) develop a configuration space model that utilizes successive bifurcation to compute the striation sizes and their number to generate realizations of a structured medium. The bifurcation rule is intimately related to the instability mechanism that generates ionospheric structure.…”