Meteor fluxes and visual magnitudes from EISCAT radar event rates: a comparison with cross-section based magnitude estimates and optical data

Abstract

Abstract. Incoherent scatter radars (ISR) are versatile instruments for continuous monitoring of ionisation processes in the Earth's atmosphere. EISCAT, The European Incoherent Scatter facility has proven e ective also in meteor studies. The time resolution of the radar can be reduced to a few milliseconds, su cient to resolve the passage of individual meteors through the narrow ISR beam. Methods for group and phase velocity determination of the meteoroids and the discrepancy between the results related to the target behaviour are presented. The radar cross sections of echoes associated with moving meteoroids (``meteor head echoes'') are very small and increase with decreasing wavelength. The parent meteoroids are found to have visual magnitudes far below the detection limit of most optical observations. The equivalent visual magnitude limit of the smallest objects observed by EISCAT in the current experiments has been estimated by two di erent methods, both from the cross-section measurements and from the measured event rates. Both methods give a limit value of +10 for the smallest objects while the upper limit is +4. The lower limit of the visual magnitude for the collocated optical measurement system is +4. Thus the two detection systems observe two di erent meteor size ranges, with the radar almost reaching micrometeorite population. Meteor¯uxes estimated from the event rates and the radar system parameters agree well with previous extrapolated values for this size range.

The EISCAT meteor-head method – a review and recent observations

“…This paper and Pellinen- Wannberg et al (1998) show how meteor head echoes are seen in raw electron time series versus altitude plots both during quiet and during weak auroral activity conditions (see Fig. 1 adapted from Pellinen- Wannberg et al, 1998).…”

“…There were some studies done in the 60's at 300 MHz by Greenhow and Watkins (1964) and at 440 MHz by Evans (1965Evans ( , 1966 without any follow-up for many years. EISCAT observations on the Geminid and Perseid meteor showers in 1990, 1991 and 1993 started a new era of meteor studies on HPLA radars Wannberg, 1994, 1996;Wannberg et al, 1996;Pellinen-Wannberg et al, 1998;Westman et al, 1997). Almost simultaneously meteor observations were performed at Jicamarca (Chapin and Kudeki, 1994a, b) and at Arecibo (Zhou et al, 1995;Mathews et al, 1997;Zhou and Kelley, 1997).…”

“…Even other EIS-CAT measurements report possible meteor echoes (Malnes Correspondence to: A. Pellinen-Wannberg (asta.pellinen-wannberg@irf.se) et al, 1996). EISCAT observations have continued during , 1998and 1999Leonids (Pellinen-Wannberg et al, 1999Janches et al, 2002a). Recently a series of systematic tristatic dust measurements started.…”

“…EISCAT raw electron density time series versus altitude showing both meteor head echoes (sharp peaks) and weak auroral precipitation (between 00.21 and 00.23 UT and between 00.34 and 00.39 UT). (Adapted from Pellinen- Wannberg et al, 1998) Fig. 1.…”

“…Using 13-baud Barker codes offers a possibility for very accurate instantaneous velocity measurements of the meteors . Using the tristatic UHF system for such measurements, the full vector velocities of the meteors passing the common tristatic measurement volume can be resolved (Pellinen-Wannberg et al, 1999), revealing whether the particle has been bound to the solar system and to a comet or if it comes from interstellar space (Janches et al, 2002a, b). The particles observed with this method are in 0.1-1.0 mm size range corresponding to a visual magnitude range of +10 to +4.…”