Correlation between cosmic noise absorption and VHF coherent echo intensity
Résumé
The HCPs are observed more frequently during the winter months, which, combined with the fact that VHF echoes observed during HCPs exhibit features typical for field-aligned E-region irregularities, makes their association with the polar mesospheric echoes (for which some positive CNA/SNR correlation has been reported in the past) very unlikely. Instead, we attribute the high positive CNA/SNR correlation to the synchronous, to a first approximation, variation of the particle fluxes for two different but close sets of energies.
By considering the dependence of the CNA/SNR correlation coefficients for both VHF radars (CA1 and CA2) upon the correlation between SNRs for two radars (C12), we show that both coefficients, CA1 and CA2, and the agreement between them decrease drastically with a C12 decrease, which we interpreted through the progressively increasing role of the spatial inhomogeneity of the processes leading to the enhanced CNA and SNR. In this situation, a similarity between the radio signal collection areas should become important, and we demonstrate that the HCP occurrence and mean correlation coefficient decrease as the riometer beams and radar cells become less comparable in terms of mutual orientation and closeness between the points of maximum sensitivity.
Keywords. Ionosphere (Auroral ionosphere; Particle precipitation; Instruments and techniques)