An unexpected outburst of Perseid meteors was detected using video observations in low light conditions on August 14, 2021. The flare peaked at a solar longitude of 141.474 ± 0.005 degrees (equinox J2000.0), and the activity profile had a full width of half a maximum of 0.08 degrees solar longitude and a peak velocity of ZHR = 130 ± 20 per hour, which is ~ 45 in hour.
The Perseids had a steeper distribution index in size than the usual annual flow rate. The activity profile is similar to the profile obtained from visual and direct observations of meteor scattering. This activity may be related to earlier smaller gains seen in 2018 and 2019.
In 2018, visual observers recorded a narrow peak in the Perseid stream activity in the region of solar longitude 140, 95 °, about ~ 30 hours after the traditional maximum of the Perseids, with a peak near ZHR = 25 per hour, which is higher than the usual Perseid activity at this time, constituting ZHR ~ 45 per hour (Miskotte 2019). In 2019, a similar peak was recorded in the forward scattering observations of meteors collected by the International Radiometeor Observation Project. The flare peaked at 141.02 ° solar longitude that year, with a peak ZHR ~ 30 per hour above normal (Miskotte 2020a; 2020b).
In this case, we report the discovery of a larger outbreak on August 14, 2021 (Jenniskens, 2021). This flare was not expected from the known flares of 109P and the Swift-Tuttle dust trail.
The Perseids are best observed from the northern hemisphere. The 2021 outbreak occurred between 6:00 and 12:00 GMT on August 14, 2021, at a time most suitable for video observation networks of the CAMS meteoroids in the United States. The networks triangulate meteors using video cameras operating in low light conditions and determine the radiant and speed of the meteor during continuous night observation. The weather was mostly clear for the networks in Texas (coordinated by W. Cooney, including D. Selle, F. Sirway and J. Brewer) and California (P. Jenniskens, D. Samuels, J. Albers, E. Egland, B. Grigsby and J. Vray). CAMS Mid-Atlantic (coordinator P. Gural), CAMS Florida (A. Howell), CAMS Arkansas (L. Juneau) and LO-CAMS in Arizona (N. Moskowitz) also observed some meteors in partially clear skies (see CAMS- website for August 14).
The first results of the new CAMS network in Texas with clear sky and CAMS network in California with clear air show an activity profile with a peak zenith hourly speed of ZHR = 130 ± 20 per hour over the usual ZHR = 40-45 per hour of annual Perseid activity (Fig. 1). The full width-half maximum of the Lorentzian profile is 0.08 ± 0.01 degrees solar longitude. The peak fell at 141.474 ± 0.005 degrees solar longitude (equinox J2000.0), which corresponds to 8.2 hours GMT on August 14. The combined magnitude distribution index was 3.59 ± 0.36, compared to 2.94 ± 0.04 for the annual component in other years at this solar longitude.
Comparison with other observations
Pierre Martin, a visual observer from Ottawa, Canada, reported "many Perseids per minute with a lot of bursts, sometimes 3-4 per second," starting at 6:00 GMT. He observed until 9 o'clock GMT, with a clear sky and the limiting magnitude of 6, 7. Based on his readings with a 5-minute interval, we calculated the peak ZHR = 210 ± 20 per hour at a solar longitude of 141, 474 ± 0, 005 degrees. Visually observed meteors closely follow the video data profile (Fig. 2).
This outburst was also confirmed by direct radio observations of meteor scattering by H. Ogawa of the International Radiometeor Observation Project.A compilation of data from 49 observers from 14 countries showed that the number of detections increased above normal levels after 6.4 hours GMT (141.40 degrees solar longitude) and peaked at about 8.18 hours GMT (141.49 degrees) at a level 3 times higher than the peak level of the Perseids, after which it decreased to a normal level at 12, 5 hours GMT (141, 65 deg. solar longitude). Zenith's combined hourly rates peaked at around ZHR = 210 per hour.
The outbreak cannot yet be identified with the known intersection of the 109P / Swift-Tuttle dust trail. On the other hand, the width of the flare is similar to that of the returning Perseids (Jenniskens, 2006). The Filament is believed to be a collection of dust in resonance with the mid-motion from many past comebacks. Perhaps this means that this year this dust was directed towards the path of the Earth. These observations may help to better understand the origin and evolution of this dust component.
Jenniskens P. (2021). "Perseid meteor shower outburst 2021". CBET 5016, 2021 August 14, editor D.W.E. Green.
It is noteworthy that the last outbreak occurred only a few years ago, and that the origin of this particular outbreak was not expected and its origin has not been established at this time.