Radar observations of the 2011 October Draconid outburst

Abstract

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 multi-station Draconid echoes and 179 single-station overdense Draconid echoes (covering the magnitude range of +3 M V +7) between 16-20h UT on 2011 October 8. The mean radiant for the outburst was determined to be α g = 261.9 • ± 0.3 • , δ g = +55.3 • ± 0.3 • (J2000) from observations of the underdense multi-station echoes. This radiant location agrees with model predictions (e.g. to ∼ 1 • . The determined geocentric velocity was found to be ∼ 10 − 15% 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 (2004). From these model comparisons, we find that Draconid meteoroids at radar sizes are consistent with a fixed grain number n grain = 100 and a variable grain mass m grain between 2 × 10 −8 kg and 5 × 10 −7 kg, with bulk and grain density of 300 kg · m −3 and 3 000 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 1 000 with grain masses between 10 −10 and 10 −9 kg, and a total mass of 2 × 10 −6 kg.

Precision Measurements of Radar Transverse Scattering Speeds From Meteor Phase Characteristics

“…Validation of the PSSST method has been done by comparing the computed speeds of meteors from four showers to the speeds for those same showers reported by Schult et al 2018and Ye et al (2013). The PSSST…”

“…Since the Draconids tend to be fragile, they will decelerate more quickly than more compact and less fragile meteoroids. The work of Ye et al (2013) corrects for this to give the preatmospheric, deceleration‐corrected, v ∞ speed (23.27 km/s) shown by the dotted line on the Draconid panel in Figure 21. The deceleration‐corrected speed will always be higher than the peak of the distribution of observed speeds and the trend should become asymptotic with v ∞ as height increases.…”

“…We take the most probable preatmospheric speeds for these showers to be those found by Schult et al (2018) from MAARSY head echo measurements, as head echoes are recorded by MAARSY at comparatively high altitudes (Figure 21) and hence suffer little from atmospheric deceleration. For the Draconids, we examine speeds found by Maslov (2011) and Jenniskens et al (2011) as well as the most probable preatmospheric, deceleration‐corrected, v ∞ speed from Ye et al (2013).…”

Meteor Shower Forecasting in Near-Earth Space

“…While several Draconid outbursts and storms have been correctly predicted -including the recent 2011 outburst [37] -the Draconids have a history of being unpredictable. For instance, activity in 1972 was much lower than anticipated and predictions of activity in the the 70s and 80s did not occur [5].…”

The 2011 Draconids Meteor Light Curves and Meteoroid Fragmentation

“…The observers around the globe became active and various observations confirmed the predicated outburst (e.g. Koten et al 2012;Kero et al 2012;Ye et al 2013).…”