We’ve already seen that there are very long term lunar cycles that sure look like they drive the weather changes on 1800 year (and longer) cycles. Even with shorter “spikes” on the graph of particular pulses of tidal forces. (All stirred by the planets and orbital resonance that keeps things in sync, so the Sun, too, has participation in some of the cycles, like the 179 ish year one).
But at the short end, lunar cycles tend to things like a 29.5 day lunar month, and the 19 year Metonic Cycle. Hardly the stuff of 60 year PDO / AMO cycles.
The eclipse calendar tends to be set by the Saros Cycle that’s a bit over 18 years.
Fortunately for early astronomers lunar and solar eclipses repeat every 18 years 11 days and 8 hours in a “Saros” cycle.
That bit about eclipses matters. That is when the moon is crossing the ecliptic. Other than that time, it is above or below the ecliptic and pulling water more north or south.
For comparison, the Metonic Cycle (per the wiki) is more about getting the lunar months (13 of them) and the solar months (12) to sync up every so often:
For astronomy and calendar studies, the Metonic cycle or Enneadecaeteris (from Ancient Greek: εννεαδεκαετηρις, “nineteen years”) is a period of very close to 19 years which is remarkable for being nearly a common multiple of the solar year and the synodic (lunar) month. The Greek astronomer Meton of Athens (fifth century BC) observed that a period of 19 years is almost exactly equal to 235 synodic months, and rounded to full days counts 6940 days. The difference between the two periods (of 19 years and 235 synodic months) is only a few hours, depending on the definition of the year.
Having your ‘count’ match up again isn’t quite as important to tidal forces as is what end / side of the earth you are tugging upon.
Jumping To A Conclusion
I sent some fair amount of time looking at Metonic cycles (btw, I think that’s the wrong place to look), the 19 counter holes at Stonehenge, pondering Celtic Calendars and Druid Festivals ( just sent in a thesis for a Master of Druidism, BTW, so with luck, I can soon be called ‘Master Druid’ or maybe M.o.D. ;-)
That Saros cycle is the one that has the moon vs earth and sun as the basis.
So, OK, why not an 18.x cycle then? Why a 60 year cycle?
Well, first off, in another discussion we saw that it’s really a ‘sort of a 60’ and has a significant ‘near 55-59’ component. It is something of a ‘quasi cycle’ at that. And the ‘typical’ period is averaging shorter than 60 years.
The obvious thing to do is divide by 3. (Or multiply by 3 going the other way). That gives about 54 years. Still, sometimes you get a cycle split between things, like an intercalary month in lunar / solar calendars.
But why 3? That damn number keeps coming around. From the Druids (who memorized things in threes a lot) to Tesla who as fixated on it and only slept in rooms with 3s in the number).
I looked more closely at the definition of the Saros Cycle.
Note also that the saros (18.03 years) is not equal to an integer number of revolutions of the Moon with respect to the fixed stars (sidereal month of 27.32 days). Therefore, even though the relative geometry of the Earth-Sun-Moon system will be nearly identical after a saros, the Moon will be in a different position with respect to the stars. This is due to the fact that the orbit of the Moon precesses.
A complication with the saros is that its period is not an integer number of days, but contains a multiple of ⅓ of a day. Thus, as a result of the Earth’s rotation, for each successive saros, an eclipse will occur about 8 hours later in the day. In the case of an eclipse of the Sun, this means that the region of visibility will shift westward by 120°, or one third of the way around the globe, and the two eclipses will thus not be visible from the same place on Earth.
Because of the ⅓ fraction of days in a saros, the visibility of each eclipse will differ for an observer at a given locale. For the lunar saros series 131, the first total eclipse of 1950 had its best visibility for viewers in Eastern Europe and the Middle East because mid-eclipse was at 20:44 UT. The following eclipse in the series occurred approximately 8 hours later in the day with mid-eclipse at 4:47 UT, and was best seen from North America and South America. The third total eclipse occurred approximately 8 hours later in the day than the second eclipse with mid-eclipse at 12:43 UT, and had its best visibility for viewers in the Western Pacific, East Asia, Australia and New Zealand. This cycle of visibility repeats from the initiation to termination of the series, with minor variations.
That tiny little hard to read fraction is 1/3 or 8 hours of rotation.
That’s why it takes 3 of them for a full cycle. Having a large tidal pull on the bottom of the Atlantic does not do the same thing as a large tidal pull on the bottom of the Pacific. It takes 3 cycles to get back to the same place (more or less).
That’s why it’s a (roughly) 3 Saros cycle pattern and likely why the AMO swaps out of sync with the PDO. Tug one, wait for the bulge to move one ocean over, tug again…
There are other, longer term orbital movements that cause the whole “Saros Series” to take even longer to fully repeat. During that time, each 18.x and 60 ish year “cycle” will be slightly different from the ones before and after. In those kinds of circumstances, you tend to get ‘quasi cycles’ and I’d not be at all surprised to find an intercalary 18 or 9 years on one vs another PDO swap. If things get a bit out of sync (and that is not an exact 1/3 …) there will be the occasional intercalary event as the two moving cycles establish a new ‘sync’ point. Perhaps even the occasional ‘skip beat’.
On the longer term, the exact alignment of the moon and earth has the moon drifting more north and more south on a very long cycle. That will slop water more north and more south (and influence things like the Circumpolar Current depth and the Antarctic Circumpolar Wave http://www-das.uwyo.edu/~geerts/cwx/notes/chap11/ant_wave.html that runs in about a 1/2 Saros cycle.
So there are opportunities for many interactions with land forms and ocean bottoms, winds and atmospheric tides too.
It takes between 1226 and 1550 years for the members of a saros series to traverse the Earth’s surface from north to south (or vice-versa). These extremes allow from 69 to 87 eclipses in each series (most series have 71 or 72 eclipses). From 39 to 59 (mostly about 43) eclipses in a given series will be central (that is, total, annular, or hybrid annular-total). At any given time, approximately 40 different saros series will be in progress.
I find those two numbers fascinating. First off, we’ve got a number rather close to Bond Events. 1470 +/- a couple of hundred and often stated as 1500 years. So at one end of the longer Saros Series length. With an error band of about the distance to the other end of Saros Series length. Then we’ve seen various “about a 1000 years” patterns in weather history and human history from that. Very near the other shorter end of the Saros Series.
It don’t think it that big a ‘leap’ to think that when at an extreme end of the lunar excursion, and it swaps back the other way, there might be an extraordinary “slop” in the oceans trying to follow it. Perhaps even enough to disrupt where the Gulf Stream plunges down off Greenland, or where ice shelves suddenly lift and crack off (many of the long cycle events are measured by ‘ice rafted debris’).
The precession of the lunar orbit takes 18.6 years, so only when the precession aligns with the Saros cycle at an extreme tide will we get maximum tides.
With the culmination of the 18.6-year cycle of the Moon in 2006 and again in 2024-25, also called the Major Lunar Standstill, we are afforded the unique opportunity to observe the monthly, annual, and 18.6-year wanderings of the Moon. The 18.6-year cycle is caused by the precession of the plane of the lunar orbit, while this orbit maintains a 5° tilt relative to the ecliptic. At the peak of this cycle, the Moon’s declination swings from -28.8° to +28.8° each month. What this means is that each month for the years 2005-2007 and also 2023-2026, the Moon can be seen rising and setting more northerly and also more southerly than the solar extremes, and will transit monthly with altitudes which are higher in the sky than the summer Sun and lower in the sky than the winter Sun.
It is when that 18.6 year precession cycle lines up just right with the solar alignment 18.03 year Saros Eclipse cycle state (i.e. maximum lunar declination changes and maximum lunar / solar tidal forces aligned) that we ought to get major effects and events.
This is the Greenland Gisp2 record:
Most of the time we’ve seen this, I’ve pointed out the down dips and collapses of civilizations. Instead, look at the peaks this time. Starting from the deep past at the far right.
10,000 BP rise out of the snowy muck.
9,000 BP a nice high peak.
7800 BP another peak (about 1200 years offset from prior peak).
6900 BP another peak
5000 to 6000 BP as a similar ‘multi-peak’ look to 9000-10000 but flatter due to no longer rushing out of a glacial. Still, it has small relative peaks on the 5000 and 6000 points.
4200 BP nice peak, about 1000 years away from the early side of the broad peak near 5000-5200 BP
3250 BP Peak
2100 BP Peak (about 1100 years from prior)
1000 BP Peak (about 1100 years from prior)
0 BP Peaking at present (though in the context of ‘lower highs’ as we past peak temps about 3500 or 8000 years ago).
There’s clearly some “other stuff” going on too. Like that “swoon” between 4000 and 6000 BP. So some longer cycles and other events need inspection (like, perhaps, that 5000 year lunar cycle as it aligns with other orbital shifts seen in the earlier paper). Still, to my eye, there looks to be an ‘about 1000+ year’ warm spike. Sub-multiple of 3000 years (or 2 x that 1500 year cycle) or perhaps just a couple of hundred years error in the ice off of that 1226 year cycle. I don’t know the error bans on the GISP2 core.
It is also possible that other things, forces, cycles modify the basic Saros “long count” and / or provide ‘skip beat’ modifications.
Still, at a ‘first cut’, it looks to me like there is plenty of room for a “long count” Saros Series causality on the major warm peaks, and a “short count” Saros Cycles on the PDO / AMO “near 60 year” cycles. I’d even go so far as to say that slopping loads of ocean back and forth has a better chance of explaining small Length Of Day variations than all that stuff and nonsense about winds and all. Just not enough mass in the air. But move some North Pacific water to the Equator, now you have something to work with.
It would be good to get real numbers with real error bands on all of it. From Saros series of cycles exact dates to Gisp2 exact dates with error bands. Match up with the known PDO / AMO / AO / Circumpolar wave / etc. dates and tide charts. Fit the whole jigsaw machine together in computer animation / simulation and see what happens.
Anyone got a few $Million NGO Grant to spare? Doing this on a laptop in my living room is getting old ;-)
(Then again, I get the feeling I’m finding more useful things than ‘the other guys’ at government funded labs; in part as I’m not dealing with any “overhead” people or organization…)
I think it is the case that the reason the PDO/ AMO swaps on a quasi-3-Saros basis is that it takes 3 periods for the lunar tidal forces to be back over the same ocean at the same point in the Saros cycle. I think it likely that other resonances with lunar tidal cycles will be found. The Antarctic Circumpolar Wave looks to be running on about 1/2 a Saros frequency.
It looks likely that recognition of lunar tidal cycles longer than “the month” is an important thing to weather and ocean changes. Depth, mixing, current, precipitation; all those and more can be shifted, shaped, and modified by tidal force.
This graphic is an animation (if it works right ;-) that shows how the point of the eclipse moves over the earth during a Saros series. That is also the point in direct alignment with the moon and sun, so ought to have the most direct tidal force. Various eclipses in each cycle and series. It is the net-net of all those wandering forces that stirs the world oceans.
Notice that this runs about 1200 years from one end of the earth to the other. Each Saros cycle 18.03 years, and the Series taking that 1226 years before repeating.