The Atlantic has been running warm lately, but that’s because there’s been little happening with Nature’s natural heat transporters. WUWT commenter SteveM pointed out something interesting in the latest SST image from NESDIS, but before we have a look at the animation I developed from that imagery, I thought we should have a look at the role that hurricanes play as heat engines.
First an animation from Goddard Space Flight Center:
And another, showing how the heat transport and surface cooling process operates.
From NASA SVS: As water vapor evaporates from the warm ocean surface, it is forced upward in the convective clouds that surround the eyewall and rainband regions of a storm. As the water vapor cools and condenses from a gas back to a liquid state, it releases latent heat. The release of latent heat warms the surrounding air, making it lighter and thus promoting more vigorous cloud development.
Now let’s watch this simple animation of the last two weeks of Sea Surface Temperatures and you’ll see the cool water tracks left by hurricanes Daniel and Earl:
You can see the cool tracks in the last frame. Note also the large and growing La Niña off the west coast of South America. It’s turning deep purple and on to black. Way cool.
Wave motion in the oceans occurs on all scales and depths it is not just surface waves, that need to be considered. Large surface waves could interact with deeper waves which exist below the surface.
The “mixed layer” of the ocean extends to about 1500 ft depth, and exists because various mechanism thoroughly mix that top layer of water, so that it has relatively uniform temperature and relatively small density differences.
http://www.villasmunta.it/oceanografia/the_three.htm
http://web5.cns.utexas.edu/news/2008/06/
http://my.opera.com/nielsol/blog/2010/07/17/internal-ocean-water-mixing
If you consider all these effects it is not at all unreasonable that there are large vertical displacements induced by very large surface waves and other effects like salinity, density due to thermal cooling by evaporation, and salinity changes due to either dilution from rainfall or evaporation of water from warm water where little rainfall is present.
As noted above a hurricane or typhoon would create a very complex environment due to its presence. Plunging surface waves when breaking would impart downward momentum as the crest breaks. The breaking action would also create non-uniform density due to aeration of the water, as this plunging breaker drives air bubbles deep below the surface. In the area near the eye wall you have very high speed winds evaporating water from the sea surface both cooling it and increasing its salinity. Add to that the barometric pressure difference tending to pull water up in the eye of the storm and the wind driven surge on the “right hand side” of the storm would create conditions that would be likely in my view to cause over turning of the surface water as it attempts to find equalibrium.
The high winds would first rapidly cool the surface layer and evaporate water from it increasing its salinity, upsetting the relatively stable mixed layer with a high density surface layer over a lighter warmer pool of water. Add in a little wave action to provide initial vertical motion and the density difference would provide the rest of the energy to drive the sea water equivalent of a down burst.
In areas where you have torrential rain fall of nearly fresh water falling on the surface of the water you also have to consider the density changes due to the cooling of the rain as it falls from high altitudes. That cold fresh water, mixed with a little surface salt water could also create an area of density instability which could over turn some of the surface waters bringing warm water up from below and the cooler mixed layer on the surface due to wind and rain plunging down until it finds equilibrium.
I am aware that the first paper was “only” a numerical simulation, but I have a lot more faith in the empirical evidence of an submarine sailor getting tossed about in his boat well below the surface than I do assertions that very large waves cannot cause significant mixing below the surface.
Obviously it would be nice to find a study where someone actually did measurements of turbulent mixing during a major wind event but so far the pickings seem to be thin with regard to actual physical data in that regard.
Larry
This has proven to be a fascinating thread. My eyes are tired staring at my laptop LOL.
But thanks to George E. Smith, Wade, DP, Hotrod, Mike Lorrey, Caleb and others for the cool discussion.
Chris
Ha. I said “Wade” I meant “Wayne.”
Tired eyes….and tired brain.
Chris
savethesharks says:
September 8, 2010 at 8:50 pm
Tired eyes….and tired brain.
Chris
Mine too.
And Anthony, thanks for an interesting and relevant article!
hotrod (Larry L):
September 8, 2010 at 8:09 pm
Good description!
I agree on the more long-term deep wave mixing effects but I’m going off a link given a few articles ago to a great paper showing satellite IR tracks of hurricanes with temp scales intact. These hurricanes were tracking behind at about -5ºC and I just don’t think if the depth of vertical mixing were many hundreds of meters THAT much energy is moved to space. Now that would be one whole lot of joules! (and would take a long, long time to warm back, multi-years) That’s what I meant about the top few x meters, speaking just on the amount of energy that one hurricane could possibly move vertically and out to space.
Now the jostling back and forth, locally up and down, much deeper to hundreds of meters as the roots of the waves pass, that make sensible and I’ve read correct in what you were saying.
I had always though that the deep mixing was by currents, slow and persistent movers, mainly north and south in the Atlantic and Pacific specifically, and the moon, picking up the entire ocean a few millimeters and then letting it go, twice a day, every day, that doing the primarily east-west movements. It’s the shallower sloping continental shelves where the main mixing would occur. Water pulled up the slope, released to move back down. Guess if you computed the total amount of water moved daily by the moon’s gravity it would so totally dwarfs that moved by a mere single hurricane, but, hurricanes we can actually see in live action and just look what they alone can do! But the tides and currents are so slow and gradual that if you don’t live right on the coast and the land slopes are shallow you never notice them at all.
Paul Birch says:
September 8, 2010 at 6:37 am
“I can understand why a following hurricane might be weakened by cooler waters, but I don’t see why this would slow it. Repulsion between the two vortices (if they are rotating the same way) might do it.”
I think I’ve got that the wrong way round. Vortices of the same sense attract. So the following hurricane ought to speed up, not slow down.
Paul Birch says:
September 8, 2010 at 6:37 am
I think I’ve got that the wrong way round. Vortices of the same sense attract. So the following hurricane ought to speed up, not slow down.
As adjacent air?
WATCH OUT. East Coast ! (Again)
http://www.osdpd.noaa.gov/ml/air/index.html — look at the Aerosol Daily !
Saharan Dust is going SOUTH again. Like just before Earl.
Remember, the El Nino made this a SUPER-season for Hurricanes – – in water temp.
BUT then also made Saharan Dust Storms, which Killed them – – just like 1998. It happens when the El Nino is TOO strong.
This year, we’ve had dust as far as the WESTERN Caribbean, most days ( ! ) (see aerosol Monthly)
“”” George E. Smith says:
…..Sometimes I wonder why I bother to post this stuff; it apparently doesn’t get read by anybody besides Chasmod….”
Oh, it gets read. I always pay special attention to what you have to say.
Lee Kington says:
September 9, 2010 at 5:23 am
Paul Birch says: “I think I’ve got that the wrong way round. Vortices of the same sense attract. So the following hurricane ought to speed up, not slow down. ”
“As adjacent air?”
Bernoulli effect. If the air in the vortices is trying to circulate past each other, as in your diagram (vortices have same sense), it is squeezed into a narrower channel, so goes faster, so sucks harder, causing the vortices to orbit each other. Whereas if the air is going the same way (vortices have opposite sense) it can spread out more, going more slowly, thus increasing the pressure and causing the vortices to repel each other. I think that’s roughly the mechanism. I may not have got it quite right, though – I’m not entirely happy with it.
Bob Tisdale says:
September 8, 2010 at 7:25 am
I wanted to call your attention to the graphs you show in your website, as in:
http://i51.tinypic.com/osgvop.jpg
NINO3.4 SST Anomaly
Monthly Change = -0.22 deg C
it appears only a difference of about 1.5 degrees between the peak of 1998 and 2010, what seems to be a most convenient GWR graph, as the real difference between the two Ninos, where I live , in the 1+2 area, the maximum temperature in 1998 it was 39 C, while this year was 29 C, a difference of TEN degrees centigrade LOWER than in the 98 El Nino
How do you explain that? or is it Statistics Magic?
Chuck near Houston says:
September 8, 2010 at 9:52 am
Stole my line! 😉 I cannot understand why all the weather forecasters still call it “ee”gor instead of “eye”gore!
Concerning this discussion of hurricanes cooling the ocean surface; and turbulent mixing with the cool deep ocean waters.
Don’t assume that I think those deep waters just sit there forever. Even due to just tidal movements; the whole oceans have to be in a constant non-equilibrium condition; and probably at all scales.
In the most simple model of waves on water, pure “gravity waves” require nothing more than gravity acting constantly downward on each water molecule as it is displaced up and down affected by just gravity and local buoyancy to try and return to a level surface equilibrium state.
So although the waves are moving along the surface; maybe at 400 miles per hour even, the water isn’t moving along the surface; it stays in the same place. So a wave coming over to Califonia from Hawaii, is not bringing any Hawaiian water with it.
A more accurate physical description of water waves will show that in fairly ordinary water waves, an individual molecule actually runs around in a roughly circular orbit (in the plane of the wave travel direction); so even though on average the molecule doesn’t go anywhere; instantaneously it is moving in this orbital motion. And as you might expect, the amplitude of that circle depends ont he amplitude of the wave. So that alone means there is a vertical mixing right at the surface layer; but this is very much smaller amplitude than the total depth at which the pressure waves of the storm can be sensed down deep.
It is easy to relax into a simpler one dimensional model of the ocean, and think of it as simply a stack of water layers; each with a different temperature. Waters that are tens to a few hundred metres are still transparent to some parts of the solar spectrum so that allows a lot of energy to be deposited many tens of metres down, and that should cause local heating, and expansion, resulting in a vertical convective gradient. But in a one dimensional view, why would anything really move. Well of course the ocean is not nice and stably one dimensional, and somewhere that upward convection will manifest itself and covey the solar warmed water back to the surface; where evaporation can probably put some of it into the atmosphere. Of course surface waters that have alread cooled for some reason will dive to make up for the vertical convection. Kirchoff’s Law has to be obeyed or the water would stack up somewhere. When you add in the tidal driver due to the rotating earth, then it is obvious that the oceans can’t settle down to any stable one dimensional state.
I’m not a cosmologist; but I am under the impression that Sir James Jeans did a famous calculation wherein he proved that any large enough amount of matter (gaseous mass) that is all attracting itself gravitationally must become unstable and undergo gravitational collapse; which is how star formation gets going in the first place. But note that that collapse is NOT well behaved, squishing everything into a single massive black hole; the large mass breaks up into chunks; which individually collapse.
I suspect that somewhere in there is the concept of the velocity of sound waves; and that material can only move under the drive of its self gravity, at a certain rate; so information about the collapse cannot be transmitted across the space; to tell those clumps “over there” that they are out of step. It is that finite velocity of propagation of information that stops the whole thing from dancing like the Rocketttes.
Yeah I know it’s a lame image; but I don’t have any colored sands for my beach stick to draw with.
That Jeans chap sure got around. In addition to an early exposition of the radiation spectrum of heated bodies (pre-Planck) he also did a classic derivation of the low temperature specific heat of solids. and then there is that cosmic collapse exposition. All I can remember about the derivation of the specific heats of solids at low temperature, is that you have to calculate the number of degrees of freedom in some mass of material (probably a mole) and assigns some KT or similar energy to each. Somewhere in the process, you get entangled with a square root of some expression; which would be easy to simplify; if you just replaced one of the factors in there with unity (1). Then it simplifies to somethign recognizable. The only problem is that that factor which you made equal to 1 is Avogadro’s number; 6.023 .10^23 That’s some approximation; even for Dr James Hansen.
Well the expression of which this pesky Avogadro’s number is a nuisance factor happens to contain factorial of Avogadros’ number. Now all of a sudden 1 is a rather reasonable value to use to get rid of that annoyance. Other than that, I remember nothing at all about the Jeans derivation.
But back to the water fights; the local turbulences kicked up in Hurricanes are certainly going to do some mixing; but suppose that we declare that that mixing with deeper layers is where the cold water came from; and not the latent heat of evaporation escape. Well that means that there must be a lot of suddenly warmer deep water that was transported to the depths by that same mixing.
So Ok all you Google sleuth’s; find us some peer reviewed experimentally measured data peper(s) on the appearance of deep layers of abnormally warm water that can be found in the depths of a big hurricane track; because if mixing is the source of the cold surface waters; then most of the warm water must still be there in the depths. If you are not aware of this then remember that you first heard about it here at WUWT.
No I’m not going to hold my breath while somebody finds a reference to the post hurricane deep warm water tracks.
My money is still on the Latent heat of evaporation about 545 Cal per gram of it; I( really must convert that number to Joules some day).
hotrod (Larry L) says:
September 8, 2010 at 8:09 pm
Ocean waves propagating under the influence of gravity produce water particle motions that are inherently coherent and irrotational (i.e., particle orientation is invariant throughout the orbit). Thus, unlike shear currents, they are intrinsically a poor mechanism for any turbulent mixing. Such gravity waves require a density discontinuity for propagation. The coherent motions of internal gravity waves, which are very slow to begin with, are consequently restricted to the vicinity of a sharp pycnocline. The only waves of practical consequence found at ALL depths of the oceans are the forced soli-lunar tides, whose motions are also coherent.
Turbulent mixing is largely a wind-driven process, with wave-current interactions being at best a second-order effect. The well-mixed, oxygenated layer as firmly recognized by oceanographers (see, e.g., de Boyer Montegut et al.) seldom exceeds 100m and is much shallower in tropical seas, where cyclones originate.
Although empirical data on hurricane-produced mixing are tough to find (the Navy seldom releases submarine-gathered data), some offshore platform data that I’ve seen indicates that at 200m and below the effects of hurricanes are virtually undetected. Don’t become enraptured by trendy ideas published by academics that have more to to do with the climate-change gravy train than with proven real-world physics.