Examining the altitude dependence of meteor head echo plasma distributions with EISCAT and MAARSY

A radar campaign with High Power Large Aperture (HPLA) radars in northern Norway was performed for the Geminids 2022 meteor shower to make measurements of meteor head echoes. The MAARSY (53.5 MHz), EISCAT VHF (224 MHz), and EISCAT UHF (930 MHz) radars were all operated in a zenith pointing direction. The field-of-views for the EISCAT VHF and EISCAT UHF radars were approximately coincident. A novel meteor head echo processing algorithm was implemented for the EISCAT Manda experiment mode, providing details on the meteor head echo range, Doppler shift, and signal-to-noise ratio (SNR). The occurrence rate of meteor head echo detections for the three different systems were determined as a function of altitude. To investigate the differences in the meteor head echo detection rates, simultaneously detected meteors from the EISCAT VHF and EISCAT UHF were further examined. An altitude dependence of SNR difference between the EISCAT systems was identified and attributed to changes in the atmospheric mean free path. This data was used to determine a plasma density decay rate as a function of r^−χ, where r is the distance from the center of the meteoroid. $\chi$ was found to have a value of between 2 to 4 (1/r² to 1/r⁴). The meteor head echo detection rate differences between MAARSY, EISCAT VHF, and EISCAT UHF systems can be explained using this plasma density decay rate when the relative radar sensitivities and Rayleigh scattering effects are considered. The results have important implications for the determination of the initial mass of incoming meteoroids and the associated mass-loss rates during ablation.