2011 Leonids

Here is Alastair McBeath’s analysis of the 2011 Leonids:

With the potential for four Leonid maxima in 2011 scattered across November 16 to 18 inclusive, one of which might have produced activity in the low hundreds, albeit all with a problematically bright waning Moon, it was disappointing that weather conditions for SPA watchers globally seemed to have been unusually poor. Even visual reports to the IMO’s online data page for the shower were unhelpfully thin on the ground, with just four datapoints available between ~18h UT on November 14 through to ~00:30 UT on the 20th. At least for once, it wasn’t just Britain’s weather at fault!

These IMO results suggested merely a single Leonid peak had happened, on November 17-18, when ZHRs reached 22 ± 3. Huge gaps in the data meant this result was especially tentative however, and it would have been very easy for any short-lived outburst, no matter how strong, to have passed entirely unseen. IMO video observations proved less helpful too than might have been hoped (presented in “WGN”, 40:1 for 2012 February, on pages 48-52, especially p. 49), where only a single combined datapoint was determined for each night, based largely on European results. They indicated a single peak on November 18-19, apparently with activity still quite good by the following night. Again though, the broad timescale meant large breaks between these reports.

Looking to the radio meteor results collected by the SPA, even these gave incomplete coverage, since with observers based primarily in central-western Europe and western North America, the Leonid radiant was effectively unobservable, because of being below the horizon for all locations, from about 20h-21h until 00h-01h UT daily, a period into which fell three of the four predicted maximum timings. To hunt for what the data did show, a detailed hour-by-hour examination was made of the radio information available from November 16 to 20, concentrating on when the Leonid radiant was observable from each site. No distinct brief maxima were found on any of these dates, but activity probably due to the Leonids seemed to have been somewhat stronger than normal on November 17, between roughly 02h-13h UT, and was at its strongest on November 19 from about 01h-14h UT. (Remembering that these intervals do not show true peaks, but indicate instead the better-detectable daily period for radio Leonid meteors from the two main geographic regions represented.)

Overall, this radio meteor pattern supported the findings of the IMO video observers much better than those from the visual reports, and implied the better shower activity could have occurred on November 18-19, significantly later than any of the advance predictions had anticipated. In all cases, shower rates were apparently fairly unremarkable, which would in turn infer quite typical Leonid ZHRs had taken place, probably of the order of 15-20 or so at best, much as the visual data found. Any further results from elsewhere would be welcomed still to try to plug the gaps and see if anything unusual did happen in time to any of the late-evening-UT peak predictions.

A full list of observers whose observations were used in this analysis can be found at forum.popastro.com/viewtopic.php

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