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.