Composite equatorial spread F wave number spectra from medium to short wavelengths

Abstract

In an effort to provide a full‐spectral classification of equatorial spread F irregularities from large‐scale behavior (≈100 km) to the meter‐size domain, we have analyzed a combination of rocket and satellite data that in concert cover the complete six decade irregularity distribution. Our results provide a composite perspective in the hierarchy of processes that contribute to the total phenomenon called equatorial spread F and provide “in situ” meter‐size irregularity measurements that help explain the relationship of spectral power at short wavelengths to that in the transitional and intermediate domain. In a synoptic perspective we find that medium and intermediate domains (≈ 50 km → 200 m) display k−1.5±0.4 and k−2.4±0.2 behavior, respectively, in both vertical and horizontal distributions. The transitional wavelengths (≈200 m → 20 m) are dominated by a steep one‐dimensional k−4.8±0.2 universal drift wave spectral behavior but break at kri ≳ 1 (λ ≲ 20 m) to much higher power levels, a result that is consistent with ground‐based radar results in the meter‐scale domain. Our shortest wavelength rocket results (1 m ≲ λ ≲ 20 m) are qualitatively consistent with a lower hybrid drift wave interpretation, but the presence of resonant structure in the observed spectral distribution strongly suggests a resonant wave‐particle interaction process. While our analyses point to specific spectral indices in each of the wavelength domains, we caution against the unique identification of any spectral index with a specific geoplasma mechanism. Clearly, time in the instability growth and decay process can modify the spectral index, as can changing ionospheric conditions, transport, and diffusion. Our satellite results provide for a large statistical sampling of spectral behavior in the various wavelength domains, point to the most probable spectral indices, and highlight their variability.

A review on the numerical simulation of equatorial plasma bubbles toward scintillation evaluation and forecasting

“…Plasma density undulations with wavelengths of hundreds of kilometers have often been observed before the onset of EPB formation and have recently been termed large-scale wave structures (Tsunoda and White 1981;Tsunoda 2015). Intermediateand short-scale irregularities (tens of kilometers to the sub-meter scale) have been found to be dominant in fully developed EPBs with multiple spectral indices (e.g., Rino et al 1981;Singh and Szuszczewicz 1984;Carrano and Rino 2016). Such spectral characteristics are analogous but not identical to neutral turbulence (Kelley and Hysell 1991).…”

“…Retterer (2010a, b) tried to evaluate amplitude scintillation with a phase screen model by extrapolating the density irregularity spectra of EPBs simulated by the PBMOD. However, because the spatial resolution of the PBMOD was limited to 2.5 km at most, spectral breaks at the intermediate scale were not observed (e.g., Singh and Szuszczewicz 1984). To extrapolate irregularity spectra down to the Fresnel scale, it is necessary to reproduce smaller-scale irregularities as accurately as possible.…”

First Kinetic Simulations of Equatorial Spread-F - Analysis of Kilometer-to-Meter Scale Irregularities

“…As in situ measurements have verified, steep local density gradients exist following the development of spread-F bubbles. The spectra of density irregularities perpendicular to the magnetic field differ horizontally vs. vertically, and particularly sharp gradients (gradient length scales-n(∇n) −1 , approaching 50 m) have been measured vertically [Singh and Szuszczewicz, 1984]. The theory of collisional interchange instability explains this steepening preferentially along the vertical direction [Kelley et al, 1987].…”

Effects of Strong Scattering on Transionospheric Propagation

“…Among other important measurement techniques are groundbased polarization rotation measurements (Yeh et al, 1979), in situ measurements by rocket and orbiting satellites (Singh, Szuszczewicz, 1984;McClure, Hanson, 1973;Clark, Raitt, 1976), and radar backscatter measurements (Woodman, LaHoz, 1976). All these techniques have been used to produce a general description of the physical properties of F-region elcctron density irregularities for scale sizes from several meters to hundreds of kilometers.…”