I started with that simple question: “What does precipitation say about heat flow?” and it’s lead me to several points. The idea of a Heat Pipe Earth where we function as a pulsating heat pipe. The point that ignoring humidity causes averaging temperatures to be silly, at best. And more.
The latest incarnation is a bit more complex. It started from a smaller muse / question about California vs Florida.
In Florida, there are daily rains during the warm months. Winter not so much. In California there are cold rains in winter, summer not so much. Why are they inverted? What causes Florida to rain in summer, California not?
After a long bit of pondering, I think I ‘Have Clue’, but it’s a fairly complicated clue; and along the way other interesting patterns were seen, but only indirectly related to the California / Florida question. So this posting will have a mix of things in it. A bit more jumbled than most, but I think “they all go together when they go”. So expect things to be a bit ‘spread out’…
Where does it rain?
For major storms, we can look at the storm tracks:
That gives us the ‘tropical’ part, but not the cold storms of the North Pacific that give California rain. Still, looking at that graphic can be instructive.
First off, the tropical storms don’t stay on the equator very well. They form, and spin off to one side or the other. Tracks lead away from the equator. For some reason, the equator is dominated by forces that are not conducive to a ‘spin up’ of a major cyclone, and once a storm forms, it gets pulled toward the poles.
Next up, it’s pretty clear that they form over water and die over land. Warm tropical water is needed. But what about those two holes in the tropical south Atlantic and Pacific near South America? Well, IMHO, that’s due to the circumpolar current getting shot into the Drake Passage that then sends a cold current up the coast of South America and sends a jet of cold water out into the South Atlantic. Both keep temperatures too low for a good cyclone to feed. I think we also see the Humbolt Current cooling the central Pacific too (graph in that Drake Passage link). I don’t know if that, alone, is enough to account for the lack of cyclones in the equator band, or if it just contributes to a more complex solution, but we can observe the effect. Tropical storms form over the more stable warm water pools. Nowhere else.
Original Image from this link with a whole host of other choices at:
Comparing those two charts is instructive. We don’t get ‘Tropical Storms’ in the south Atlantic and Pacific near South America due to two cold ‘bubbles’ that push up that way. We get more ‘Tropical Storms’ in the Northern Hemisphere than in the Southern Hemisphere due to the S.H. water being colder all over and much closer to the equator. In parts of the N. Hemisphere we get fewer ‘Tropical Storms’ than expected (i.e. Indian Ocean) due to the land protruding too far into the storm areas and shoving up against the equatorial exclusion area, dampening the cyclones before they can get as numerous and large as in the large expanses of the Pacific. Basically, hot water makes cyclones. More hot water, more cyclones. Colder water, or more land, less cyclones.
Is there anything we can say about the total quantity of cyclones and what they might be saying out our temperature trends in the ocean? Do we count ‘number’ or ‘size’ or what? Well, total energy in cyclones is likely the best proxy for ‘heat flow’, and that has been measured / calculated.
down in comments from Berényi Péter there is a link to a rather interesting graph:
This comes from Global Tropical Cyclone Accumulated Cyclone Energy (ACE) according to Dr. Ryan N. Maue at the Florida State University per the link.
A casual inspection seems to pretty much say it matches what we know of temperature / warming history. It was cold in the ’70s and ACE was low. It was warm in the ’90s and ACE was high. It’s now cold again, and ACE is back in the dumper. It also looks like it follows the pattern of sunspots and solar activity too.
All well and good. But what does that MEAN.
It means that when the earth warms up, it makes a bunch of cyclones that dump the heat to space in a giant hurry and then we end up cooled off and back where we started. The heat does not hang around. It powers a giant heat pump that shoves it to the stratosphere and out into space. The added energy from a hotter sun in the 1990s with a very high sunspot cycle got neatly picked up and dumped via more cyclones. Now that the sun has gone all sleepy, the cyclones are backing off. No fuel, no pumping and dumping.
Yes, I think it’s that simple. There is no ‘heat in the pipeline’ and there is no ‘heat storage’ to speak of (in excess of equilibrium with the then current solar state). It’s ‘done and gone’ rapidly in fairly quick link with solar variation. (Yes, I think there is room from some PDO / AMO cycling, though that will mostly impact 60 year land temperature cycles. I’d wager, if we had enough data, we’d find that more heat on all those land dominated northern hemisphere thermometers would be offset by lower south Pacific ocean temperatures. I’ve seen hints of that in the limited data we do have; where there was a counter cycle in some of the Antarctic data just out of sync with the N. Hemisphere data…) At any rate, I suspect that any ‘oscillations’ need to be corrected for the geographic bias of where we measure and that the ACE does a pretty good job of matching solar variation. More “dig here”, IMHO.
But is there more?
There is a rather interesting set of graphs of total precipitation. They show total, and by month values, for the globe.
First up, the totals graph:
Well, part of what we see here is a giant band of rain right on top of the equator. More than enough local water cycling to completely swamp any desired cyclone in the formative stages. The heat is just making a giant run for the sky (with resultant downpour of precipitation when the working fluid condenses) and that just kills the cyclonic heat engine. Basically, we’ve got a different ‘regime’ of heat dumping at the very high heat loads of the equator. That, then, ‘tails off’ into cyclones in the middle tropical zones on each side where cooler and drier air can impact on the tropical air masses.
The polar deserts are remarkably defined. It just does not have much hope of precipitation as there is little heat to move the water. More heat in, more water movement. Less heat in, less water movement.
We again have the lower precipitation where the southern oceans are cooler, near South America, in keeping with the ‘heat drives a water cycle faster’ thesis. We get some interesting ‘flags’ of precipitation off the north east coasts of Asia and North America, right where the tropical storm tracks take those heat dumping engines and where the equatorial ocean current get turned north by the land. And some minor mirrors of them in the Southern Hemisphere where they rapidly quench as they reach the cooler water pools.
Once again the evidence points to “Warmth makes more rain, cool not so much; heat not hanging around.”.
One odd quirk is the high rain levels of British Columbia. That starts to get back to the question of California Rains, though, as we get their ‘leftovers’…
Before we ‘go there’ there is another tidbit from that site. You really ought to go look at all the monthly graphs. They also have a ‘big’ size available. They paint a very clear picture of progression. I’m just going to put two of them up here. It’s a clear shift with two, but the proportionality does, I think, matter. It speaks to rate of response of the system. That rate is “sub monthly” at least.
First up, June:
Next up, December:
The most obvious thing is just how the rainfall moves north and south with the sun. More sun, more heating, more rain. Movement in sync with the sun, little time delay. Equatorial max solar heat has max rains. Polar zones minimal heating, minimal precipitation. It’s a very tightly coupled system with low time lags. The other obvious thing is how central land areas get dry desert conditions if they are not in the equatorial band nor near a warm water current. Brazil, in particular, benefits from warm coastal waters and near equatorial rains. The Gulf Stream rescues Europe from a much drier climate, but I fear the Gulf Stream shifting of zones also puts parts of Saharan Africa out of the equatorial wet. (In some times during history it DOES get a load of water, though…)
I’m now going to present a bald unsupported thesis. IMHO, the cold winter rains of California (and B.C.) are the result of a heat engine controlled by the ‘cold pole’. In winter, the arctic vortex dumps a load of frozen air over a cool North Pacific, but the air is just so darned cold that the ocean, in comparison, is a ‘hot water source’, and that drives a set of cold storms to dump cold rain over the Pacific Northwest. The same effect, with the Gulf Stream and polar vortex, keeps Europe watered. In the tropics, you do not have that opportunity for the air to become so very much out of sync with the water. It is a daily cycle of sunrise, sunset; not a seasonal one as at the North Pole.
In Antarctica, you have the Circumpolar Current keeping the cold water near the pole very consistently cold and a more stable Polar Vortex that keeps the cold air more regular too. Plenty of wind, storms, and such, but foul weather kept in the ocean band where few dare to go. The northern hemisphere has an unstable polar vortex, and warm water delivered to near polar areas without a circumpolar current. The result is RELATIVELY warmer water under RELATIVELY cold air, driving the same “cyclone” production process we get in “tropical cyclones” (and for the same reasons, dumping excess ocean heat). However, this happens when the Arctic Sun sets and the cold pole of the air gets very cold, rather than during the summer sun episodes of the tropics. You can see a bit of the ‘extra heat dumping from a cold pole influence’ in the northern oceans as a bit of blue during the December chart. An interesting, if minor, artifact in the overall southward move of precipitation.
I suspect that doing some digging will find a dozen folks who’ve already found that and published on it. When time permits, I may go looking for it. I don’t in any way think this is ‘original insight’. Just my ‘discovery’ of what is likely already known.
Where I think there IS something to point out is that the band of maximum rains moves with the sun. More north in June, more south in December. The mass of blue is clearly in the Southern Hemisphere in December. Things more north in June. What does this say to me? Water is the heat engine, from oceans to clouds to rain. It dumps the heat locally, and rapidly. It is driven in sync with the solar input, and it does a very good job. There is no room in this observation for heat to be ‘stuck in a pipeline’ from air composition changes; as it’s already been pumped out to space in sync with solar flux levels. There are some oddities based on the polar vortex asymmetry of the planet. There are some oddities based on the Circumpolar Current getting squeezed up the west coasts of South America and Africa. But, by and large, heat drives a precipitation engine that keeps the planet stable. More heat in does not mean higher temperatures, it means more heat out via precipitation.
I do think there may be some opportunities for minor heat storage from long term solar input level changes. In particular, I suspect that a decades long variation in solar heating may result in an ocean out of equilibrium with a changed solar input level, that may then take years to dump the heat from those decades as excess rains.
Basically, what we have right now. ACE is way down, but flooding is up. The peak temperature in the oceans is not enough to drive us into the Tropical Cyclone regime, but the cooler air aloft is sucking heat from the oceans as wide spread rains, and flooding, due to a different solar equilibrium now. I expect this will last as long as the oceans have heat to give (from our latest hot solar decades) or as long as the sun is in a funk, whichever is shorter. This is not ‘heat in the pipeline’ so much as it is ‘equilibrium shift’ on the solar input. (In short, it takes a long time for the ocean to reach equilibrium with the solar input, but once in equilibrium it says in close sync. Changes in the gases over it do not cause changes in ‘heat storage’ as we can see the changes in precipitation tracking seasonal and decadal solar input changes; not gas changes.)
Best guess I’d give is ‘until about 2020’, then I think we will just start getting really cold as the planet adjusts to the low solar regime without our ocean heat sink to warm us. In short, the days to months cycle runs in sync with the sun rise / set and seasons. BUT the decades cycle runs in sync with solar output variations over those decades / centuries. Perhaps via a cloud modulation. Perhaps via direct solar heating of the deeper ocean waters. As the heat varies, we shift from the Equatorial Rains regime, to the Tropical Cyclone regime, to the Warm Thunderstorms regime, to the Temperate Cyclone regime, to the Cold Thunderstorms regime (and, eventually, to the Ice Age desert of ice …)
All the time with the sun driving the state, and the water delivering the heat to the sky.
At least, that’s my thesis. I’ve got a lot more to do to learn what is already known about what drives the different types of storms, where they form, what makes them more, or less, frequent. To find where I’ve got things a bit wrong and need to tweak things. But on the ‘big lumps’ I think I’ve got a bit of clue. It’s the rains and snows that dominate. IFF CO2 does anything, it can cause a very trivial fractional percent change in total precipitation. That will be completely swamped by the natural variations from solar cycling, ocean oscillations, seasonal cycling, and in the very long term, Milankovitch Cycles.
We can see that right now as globally we’ve got a lot of excess rains and snows from the recent turn of the sun making the upper air quite cold; cranking up the heat flow off planet and driving precipitation via a cooling of the ‘cold pole’. CO2 did nothing to stop it, nor to enhance it in prior years. Just came along for the ride, like the rest of us…