High‐Resolution Observation of Heater‐Induced Daytime Plasma Fluctuations at Arecibo

Abstract

AbstractIonospheric heating is known to induce density and temperature irregularities in the ionospheric plasma, which have been observed by various in‐situ and radar techniques. Analysis of incoherent scatter radar (ISR) plasma line spectra offers high resolution reconstruction of ionospheric features, but the plasma line profile is frequently difficult to reconstruct at altitudes where the heater is generating Langmuir turbulence and thus creating additional signals in the ISR spectrum. This work presents a novel, automated method based on Gabor filter image analysis to reconstruct plasma line spectra recorded with the coded long‐pulse technique. The method permits the unsupervised reconstruction of the Langmuir frequency with resolution in frequency (sub‐kHz) and altitude (∼300 m) typical of the coded long‐pulse technique even in regions directly coupling to the heater. The technique is applied to ISR data from the June 2019 Arecibo Observatory heating experiment, demonstrating the formation of field‐aligned irregularities of magnitude ∼0.5% in the Langmuir frequency during daytime conditions and spatial scale perpendicular to the magnetic field (fluctuation periodicity of several kilometers, corresponding to k ≈ 1 km−1) consistent with the patches of depletions of free electrons previously observed by in‐situ methods. Additionally, the method allows observation of the formation and evolution of the bunches over the course of several hours. Additional F‐layer irregularities were found in the ambient ionosphere in regions away from the heater coupling altitude. The automated nature of this technique offers the potential for precision analysis of Arecibo's ISR data archives for a variety of ionospheric physics applications.