Le Leonidi in futuro (Leonids 'almost-storms')
di Esko Lyytinen
Hi all, I had some time during the Christmass- and New-Year days to study the predictions of future Leonids trail encounters around the next few returns. Actually this has started in part quite a long ago. Althoug many new trails were computed now, many of the existing trails were computed earlier by Markku Nissinen. The data is not very well checked, and further modelling might considerably shift the solar longitudes of the now predicted maxima, especially with the old trail encounters.
Rob and David mention in their 1999 WGN paper, three encounter in 2033 and 2034 for the 3,4 and 5 rev. trails (included here). This study is in part concentrated to older trails. This is why, there are several more encounters given here.
As a short description I tell the following. The parent comet nodal crossing (and q) drops (as told in several contexts), by about 0.01 AU till the next return (in 2031). The situation is almost the same in 2065 and reaches in 2098 back (about) the same value it was in the 1900's.
It is probably because of this that the next storms are generally expected to happen around 2098. The situation doesn't reject the trails from crossing the ecliptic with rD>=rE around 2031 and 2065. For example with the trail from 1899 (that presently is situated most far away from the Sun (considering relatively young trails)), has this situation starting from about 2034.1 (decimal of the year). Unfortunately the situation rD=rE is not at the correct time of the year. Typically the rD varies quite quickly (in time) after all these returns, with a smaller likelihood of the Earth being at the node, when rD has the correct value. For the trails ejected in 2065 and 2098, I don't find a good encounter around the returns 2098 or 2131. So, even though storms seem possible around the returns to come, my search for the returns 2031 to 2131 din't reveal a single one clear strom. There are however several interesting encounter, some of which are not far from the storm limit and might even reach this. Most of the detected good encounters are predicted around the next return. I also found one near the storm limit after the 2065 return and another good hit with an old trail and only a single good (but old; 12-rev.) encounter around the 2098 return. I have marked (in my data-files) some encounters around the 2131 for further study. The particle density in the model was not dense enough for a good rD value. These are however oldish trails and the encounters may be below the storm limit. In general the year 2133 seems (look the graphs in the URL, below) the most favorable during this return. The encounters around 2031 were studied more carefully than the later ones, with which I was mostly interested on real storms. The good ecounter in 2068 is actually in a trail-gap in the base solution, but it does need only a very minor negative A2-effect (the Poynting-Robertson effect may produce about half of this.) to have an encouter. This has now been studied more than many of the other encouters and I predict ZHR between 600 to 1100. (Taking also into accout the modell weaknesses, the lower limit may be further lowered (to about 400 or 500?) ... and the upper rised to .. ?.)
Around the next return, the year 2034 is interesting because of 4 found encounters. Although the 10-r. ZHR is not predicted quite high, this is expected to consist of (many) bright meteors. The 12-rev encounter in 2035 has (in proportion) even more bright bolids. The year 2037 is predicted to have two strong outbursts, maybe approaching storm level. The 7-rev. encounter is now also quite well studied (better than most other encounters, with A2-effect included) and this effect doesn't seem to reduce the base modell values a lot. In part this resembles the 2001 American 7-rev. encounter (actually not the same trail), with about similar miss distance and the A2-effect dispersing only about half much, as compared to of the 2001 (but then not bringing quite to Earth orbit), and has lower mean anomaly factor).
In the next table I give the ZHR from the base modell (Lyytinen, VanFlandern) and the da0. For young trails this ZHR is expected to be about the final prediction (save for possible changes in the modell itself). For old trails the final prediction typically will be (even a lot) lower than this. I have above outlined some of the best studied old returns. For some of the oldish trails, I have in the comment column, my quess of the really expected ZHR.
Only positive da0:s were considered.
I give the solar-longitude of the nodal crossing (in 'nominal' trail) and after each year the (approximate) solar longitude longitude at the beginning of the UT day (or maybe two days given), for the approximation of the UT-time. I hope that I didn't make any typos or other errors. I you think that you find one (or more), please notify.
You can see trail-figures with all the trails ejected since 1633 included at the URSA-website; URL below. The data is not quite uniform in the original density an the trails are arbitrary cut.
Table: YYYY N ZHR in da0 comment base mod. sol.long (J2000.0). 2033 4 430 235.388 0.18 2033,Nov,13.0 sl. 235.482 2034 3 470 235.342 0.30 mostly faint meteors 2034 5 280 236.463 0.11 2034 8 310 236.164 0.07 bright, ZHR quess: 200 2034 10 380 236.478 0.04 (very) bright, ZHR quess: 100-200 2034,Nov,18.0 sl. 235.225; in 2034,Nov,19.0 sl. 236.233 2035 12 420 237.210 0.02 very bright, ZHR quess: 100 (maybe 200) 2035,Nov,20.0 sl. 236.980 2037 6 570 237.509 0.14 2037 7 810 237.293 0.13 expect ZHR approach base modell value; brightness (almost) matching 2002/7r. 2037,Nov,20.0 sl. 237.477 2038 5 180 238.651 0.22 mostly faint meteors 2038,Nov,21.0 sl. 238.224 ____________________________ 2068 9 see comm. 236.419 0.10 irreg.; estimate ZHR 600-1200 2068,Nov,19.0 sl. 236.516 2069 11 400 237.66 0.073 very irregular; bright meteors, actual ZHR ? 2069,Nov,19 sl. 237.269 2073 2 below 100 235.719 0.95 good encounter but da0 very big 2073,Nov,18 sl. 235.226 2074 8 100 240.188 0.16 quite weak 2074,Nov 23.0 sl. 240.014 2103,12 1200 238.35 0.078 disturbed, bright but actual ZHR much lower; than in the base modell. This is the only found good encounter near the 2098 return. 2103,Nov,22.0 sl. 238.558
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