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We present examples and statistical analysis of the events withstatistically significant correlation between the cosmic noiseabsorption (CNA) and the signal-to-noise ratio (SNR) of the VHFcoherent echo intensity in the area monitored simultaneously by animaging riometer and two oblique-sounding coherent VHF radars inNorthern Scandinavia. By only considering the observations fromthe narrow riometer beams comparable (in terms of the intersectionwith the ionosphere) with the VHF radar cells, we identify ~200one-hour high correlation periods (HCPs) for 2 years near thesolar cycle maximum, 2000–2001. The HCP occurrence is maximizedin the afternoon (12:00–17:00 UT, MLT≅UT+3), with the secondarypeak near the midnight (21:00–02:00 UT). Relative to the VHF echooccurrence, HCPs occur more frequently from 11:00 to 20:00 UT. Thediurnal variation of HCP occurrence is similar to that of the1-h intervals with the lowest mean absorption A<0.25dB.The HCPs are observed more frequently during the winter months,which, combined with the fact that VHF echoes observed during HCPsexhibit features typical for field-aligned E-regionirregularities, makes their association with the polar mesosphericechoes (for which some positive CNA/SNR correlation has beenreported in the past) very unlikely. Instead, we attribute thehigh positive CNA/SNR correlation to the synchronous, to a firstapproximation, variation of the particle fluxes for two differentbut close sets of energies.By considering the dependence of the CNA/SNR correlationcoefficients for both VHF radars (CA1 and CA2) upon thecorrelation between SNRs for two radars (C12), we show thatboth coefficients, CA1 and CA2, and the agreement betweenthem decrease drastically with a C12 decrease, which weinterpreted through the progressively increasing role of thespatial inhomogeneity of the processes leading to the enhanced CNAand SNR. In this situation, a similarity between the radio signalcollection areas should become important, and we demonstrate thatthe HCP occurrence and mean correlation coefficient decrease asthe riometer beams and radar cells become less comparable in termsof mutual orientation and closeness between the points of maximumsensitivity. Keywords. Ionosphere (Auroral ionosphere; Particle precipitation;Instruments and techniques

Correlation between cosmic noise absorption and VHF coherent echo intensity