The Perseid meteor shower displayed an unexpected outburst between 06:00 and 9:00 UTC on August 14, 2021, at a level of 3 times the Perseid peak level before it returned to normal levels by 13:00 UTC. This activity may be related to the earlier smaller enhancements observed in 2018 and 2019.
The outburst peaked at solar longitude 141.474 ± 0.005 degrees (equinox J2000.0) and the activity profile had a Full-Width-at-Half-Maximum of 0.08 degrees solar longitude and a peak rate of ZHR = 130 ± 20 per hour above the normal ~45 per hour annual Perseid activity, Peter Jenniskens and Koen Miskotte of MeteorNews report.1 2
The Perseids had a steeper magnitude size distribution index than the normal annual shower component. The activity profile is similar to that derived from visual and forward meteor scatter observations.
Image credit: MeteroNews
The 2021 outburst happened at a time best suited to the CAMS video-based meteoroid orbit survey networks in the United States.
The networks triangulated meteors using low-light video cameras and determined the meteor’s radiant and speed in continuous nighttime surveillance.
In 2018, visual observers reported a narrow peak of Perseid shower activity around solar longitude 140.95°, about ~30 hours after the traditional Perseid maximum, with a peak of about ZHR = 25 per hour above the normal Perseid activity of ZHR ~ 45 per hour at that time (Miskotte 2019).
In 2019, a similar peak was recorded by forward meteor scatter observations collected by the International Project for Radio Meteor Observation. That year, the outburst peaked at solar longitude 141.02° with a peak ZHR ~30 per hour above normal activity (Miskotte 2020a; 2020b).
"The cause of this outburst is currently unknown but is probably the result of an unknown filament of comet debris produced by comet 109P/Swift–Tuttle as it raced through the inner solar system many centuries ago," the International Meteor Organization (IMO) said.3
1 Strong outburst Perseids on August 14, 2021 ~ 06-09 UTC - MeteorNews
2 Perseid meteor outburst 2021 - MeteorNews
3 Unexpected Perseid Meteor Outburst on 14 August 2021 - IMO
Featured image credit: This is a composite image of meteors captured from the San Diego area between 08:00 and 09:00 UTC on August 14, 2014. This camera faces overhead and the radiant lies outside the frame to the right. The long streaks are aircraft. Courtesy University of Arizona