Micrometeor Observations Using the Arecibo 430 MHz Radar: I. Determination of the Ballistic Parameter from Measured Doppler Velocity and Deceleration Results

We present a sample of radar meteors detected during the November 1997 Leonids shower period using the narrow-beam, high-power Arecibo Observatory 430-MHz radar. During this period ~7700 events were detected over 73 h of observations that included six mornings. Near apex-crossing, 6-10 events per minute were observed in the ~300-m diameter beam. From these events a total of 390 meteors are characterized by a clear linear deceleration as derived from the radial Doppler speed determined from the meteor-echo leading-edge (head-echo). We interpret our results in terms of the meteor ballistic parameter - the ratio of the meteoroid mass to cross-sectional area - yielding a physical characterization of these particles prior to any assumptions regarding meteoroid shape and mass density. In addition, we compare these measurements with the results of a numerical solution of the meteor deceleration equation and find them in good agreement. The size and dynamical mass of the meteoroids are estimated considering these particles to be spheres with densities of 3 g/cm³. We also discuss atmospheric energy-loss mechanisms of these meteroids. We believe these are the first radar meteor decelerations detected since those ones reported by J. V. Evans (1966, J. Geophys. Res. 71, 171-188) and F. Verniani (1966, J. Geophys. Res. 71, 2749-2761; 1973, J. Geophys. Res. 78, 8429-8462) and the first ones for meteors of this size.