Radar observations of the 2011 October Draconid outburst

A strong outburst of the October Draconid meteor shower was predicted for 2011 October 8. Here we present the observations obtained by the Canadian Meteor Orbit Radar (CMOR) during the 2011 outburst. CMOR recorded 61 multistation Draconid echoes and 179 singlestation overdense Draconid echoes (covering the magnitude range of +3 ≤ MV ≤+ 7) between 16 and 20 h UT on 2011 October 8. The mean radiant for the outburst was determined to be αg = 261. 9 ± 0. ◦ 3, δg =+ 55. 3 ± 0. 3 (J2000) from observations of the underdense multistation echoes. This radiant location agrees with model predictions to ∼1 ◦ . The determined geocentric velocity was found to be ∼10–15 per cent lower than the model value (17.0–19.1 km s −1 versus 20.4 km s −1 ), a discrepancy we attribute to undercorrection for atmospheric deceleration of low-density Draconid meteoroids as well as to poor radar radiant geometry during the outburst peak. The mass index at the time of the outburst was determined to be ∼1.75 using the amplitude distribution of underdense echoes, in general agreement with the value of ∼1.72 found using the diffusion-limited durations of overdense Draconid echoes. The relative flux derived from overdense echo counts showed a similar variation to the meteor rate derived from visual observations. We were unable to measure the peak flux due to the high elevation of the radiant (and hence low elevation of specular Draconid echoes). Using the observed speed and electron line density measured by CMOR for all underdense Draconid echoes as a function of height as a constraint, we have applied the ablation model developed by Campbell-Brown & Koschny. From these model comparisons, we find that Draconid meteoroids at radar sizes are consistent with a fixed grain number ngrain = 100 and a variable grain mass mgrain between 2 × 10 −8 and 5 × 10 −7 kg, with bulk and grain density of 300 and 3000 kg m −3 , respectively. One particular Draconid underdense echo displayed well-defined Fresnel amplitude oscillations at four stations. The internal synchronization allowing us to measure absolute length as a function of time by combining the absolute timing offsets between stations. This event showed clear deceleration and modelling suggests that the number of grains for this meteoroid was of the order of 1000 with grain masses between 10 −10 and 10 −9 kg, and a total mass of 2 × 10 −6 kg.

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