The title is a bit of a play on words. In common U.S. English, there’s a frequent phrase that came, I think, from High School Sports (and eventually made it into movies). In one movie, it involves cats vs. dogs. “Cats Rule, Dogs Drool”.
But I could have causality backwards here. Perhaps the movie came first?
At any rate, this posting has two ‘themes’, if you will. First, the Tropopause dominates what happens (i.e. it “rules” while the rest of the atmosphere is along for the ride). Second, that there are things that drive the tropopause, just like there are “rules of the road”, there are physics rules that tell us how the tropopause will behave. Two sides of one coin. What are the rules that drive the tropopause, and why does that dominate the meaning of the air?
Atmosphere, Stratosphere, Mesosphere, Troposphere
My kingdom for a sphere…
We all know what a sphere is. It is a nice round ball. Radius substantially equal in all directions. The use of “sphere” in all those terms about the air layers of our planet is a lie. I’d like to make it prettier than that, but I can’t. “Reality just is. -E.M.Smith”. It is a pernicious lie that invades our understanding and corrupts the ability to see what is really happening. Yet the constraints of language force me to use those words. OK, but at least we can set a “That is a lie” marker on the “sphere” part of the words. From this point forward, when you see “Stratosphere” think “That’s a ‘polite lie’ and it’s really StratoBand”.
Why say that? Because if you let your mind be ‘trained’ into thinking “sphere” you will never see the reality, or at best see it dimly hiding behind a mental fog of wrong definition. (BTW, this is a technique I frequently use to ‘keep a tidy mind’. When I find the language is lying to me, I ‘flag it’ and create a new internal thought marker – word if you like – to link to that word that ‘clarifies’ it. From that point on, when reading that word, I hear a faint echo of the ‘synonym’ with the right truth in it… Rather like a Senator saying “My Esteemed Colleague” while thinking “That Evil Bastard” ;-)
For the StratoBand in particular, we have a clear visible case that demonstrates the lie in Stratosphere. During the winter, the polar TropoBand is essentially zero and the StratoBand extends to the surface. In essence, the TropoBand ought to be seen as a 3/4 sphere (or so) that wobbles back and forth from one end of the planet to the other. Similarly, the StratoBand ought to be seen as a 3/4 sphere (or so) that is touching one pole in a polar vortex and rising up, spinning as it goes, spreading out toward the other pole – thinning all the way. As the year progresses, this spinning vortex like band shifts from anchored at one pole to anchored at the other (so at some mid-point might well be a momentary sphere…)
Now we have a much more accurate dynamic mental model of what’s going on. No longer thinking in terms of fixed onion layers, but in terms of a spinning elastic band that surges back and forth from pole to pole. Rising and falling as it goes. That’s more nearly what really happens.
For the Tropo”sphere” it’s even more complex. It rises and falls in bands as it goes from equator toward the warm pole. These are the “Hadley Cells” and “Ferrel Cells” and “Arctic Cells”. How can something be a sphere when it is divided into at least 3 major zonal bands, each of different heights and with different dynamics, with discontinuities between them, and with a major ‘wobble’ back and forth between poles? We really have 3 different TropoBands to think about (or think in terms of).
(Details on origin below in end notes.)
OK, given that context:
What IS the Tropopause?
In the various definitions, you get a confusing mush of things. It’s the point where the lapse rate goes from positive to negative. Or it’s the place where the water vapor runs out and ozone begins. Or it’s a particular lapse rate. Or….
All well and good. But…
What does the Tropopause MEAN?
Every physical thing has some meaning. Some hidden truth. Just slapping a definition on something and ‘moving on’ rarely illuminates that meaning. Like saying “Bob is a cop”. OK. We know a little something about Bob. But is he a Narc? A homicide detective? Did he become a cop for the pension or because he likes adrenalin? What is the ‘inner meaning’ of “Bob The Cop”? For the Tropopause we hear “it is where the troposphere ends and the stratosphere begins. As though it is just some definitional artifact of two nice round ball layers.
But it isn’t.
First off, since the StratoBand comes to near ground level in polar winter, so must the TropoPause. It, too, is complicated. Second, since the TropoBandS have various heights, the TropoPause must also. Finally, since a variety of physical properties / markers change AT the TropoPause, it must be indicating something interesting about “what changed?”.
OK, hopefully I’ve gotten the ‘right word think’ into your head… From here on out, I’m less likely to actually force use of words like “StratoBand”… I’m depending on you to think that on your own when you see “Stratosphere”… OK?
Within this layer, temperature increases as altitude increases (see temperature inversion); the top of the stratosphere has a temperature of about 270 K (−3°C or 29.6°F), just slightly below the freezing point of water. The stratosphere is layered in temperature because ozone (O3) here absorbs high energy UVB and UVC energy waves from the Sun and is broken down into atomic oxygen (O) and diatomic oxygen (O2). Atomic oxygen is found prevalent in the upper stratosphere due to the bombardment of UV light and the destruction of both ozone and diatomic oxygen. The mid stratosphere has less UV light passing through it, O and O2 are able to combine, and is where the majority of natural ozone is produced. It is when these two forms of oxygen recombine to form ozone that they release the heat found in the stratosphere. The lower stratosphere receives very low amounts of UVC, thus atomic oxygen is not found here and ozone is not formed (with heat as the byproduct). This vertical stratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular convection and associated turbulence in this part of the atmosphere. The top of the stratosphere is called the stratopause, above which the temperature decreases with height.
The stratosphere is simply the place where convection is not important. The place where radiation is the dominant form of heat transfer and where radiative physics matters.
But it’s worse than that. The wiki (and I’ve seen it other places too, so it’s not just “wiki-bias”) says, in essence, that the lower bound of the StratoBand is set by where the UV runs out. Repeating, for emphasis:
The mid stratosphere has less UV light passing through it, O and O2 are able to combine, and is where the majority of natural ozone is produced. It is when these two forms of oxygen recombine to form ozone that they release the heat found in the stratosphere. The lower stratosphere receives very low amounts of UVC, thus atomic oxygen is not found here and ozone is not formed
But we know that during the Polar Winter the bottom of the Stratosphere is lower and at the Equator it is higher. Clearly “ozone formation” and UV anything are greatest in the equatorial summer and lowest in the polar winter. By the reasoning that “ozone done it”, the Stratosphere bottom ought to be LOWEST in the equatorial summer and highest in the polar winter. Besides, as someone with “The Redhead Gene”, I can assure you that a LOT of UV makes it to ground level. Tropical summer, I’ve got 15 to 20 minutes tops at noon, then I’m lobster time…
So that ozone formation / UV description is a RESULT in the Stratosphere, not a LIMIT on the lower bound altitude.
The troposphere is the lowest portion of Earth’s atmosphere. It contains approximately 80% of the atmosphere’s mass and 99% of its water vapor and aerosols. The average depth of the troposphere is approximately 17 km (11 mi) in the middle latitudes. It is deeper in the tropics, up to 20 km (12 mi), and shallower near the polar regions, at 7 km (4.3 mi) in summer, and indistinct in winter.
The word troposphere derives from the Greek: tropos for “turning” or “mixing,” reflecting the fact that turbulent mixing plays an important role in the troposphere’s structure and behavior. Most of the phenomena we associate with day-to-day weather occur in the troposphere.
The chemical composition of the troposphere is essentially uniform, with the notable exception of water vapor. The source of water vapor is at the surface through the processes of evaporation and transpiration. Furthermore the temperature of the troposphere decreases with height, and saturation vapor pressure decreases strongly as temperature drops, so the amount of water vapor that can exist in the atmosphere decreases strongly with height. Thus the proportion of water vapor is normally greatest near the surface and decreases with height.
In short, the Troposphere is where convection and evaporation / condensation dominate. Driven by ground heating. Radiation simply does not matter here. Any ‘ground heat’ is rapidly taken up by convection and evaporation / precipitation, lofted to the height where radiation takes over, and dumped. We see that every day with the daily temperature cycling in response to 0 to 1400 (ish) W/m^2 solar flux variations.
Now we can start to see what the Tropopause is telling us. It is telling us the point at which convection and precipitation have ‘done their job’ and moved the heat. It is telling us exactly where radiative physics can take over. Where the ‘heat engine’ has run down and mass movement runs out of energy.
A higher tropopause means more heat is landing on the surface. A lower tropopause means less heat is landing on the surface. It’s really that simple. We can directly measure surface heat via tropopause height. We can even see this in no uncertain terms. At the arctic in winter, there is no surface heating. The tropopause crashes into the ground. At the Equator there is strong surface heating. The tropopause is at the greatest height. Yet there is more… Thunderstorms have what is called “overshoot”. (Another broken term, IMHO). The surface heating is so large that a huge run of wet air shoots up and crashes right on through where the tropopause layer ‘ought’ to be. In my view of things, it is simply locally lifting the tropopause at the point were there’s a bit more convective / precipitation work to do do dump some extra heat to the radiative zone… Again, directly reflecting the heat load at the surface below. (This is confirmed, IMHO, by the way storms leave a cool track in their wake that is lacking in convection / precipitation…)
This has implications.
Since the tropopause responds to the average temperature of the entire layer that lies underneath it, it is at its peak levels over the Equator, and reaches minimum heights over the poles. On account of this, the coolest layer in the atmosphere lies at about 17 km over the equator. Due to the variation in starting height, the tropopause extremes are referred to as the equatorial tropopause and the polar tropopause.
I think the Tropopause guys need to go talk to the Stratosphere guys and “give them a learnin’…” ;-)
Recently, the sun ‘went quiet’ and the atmospheric height dropped. IMHO that is a direct measurement of the change in net surface heating. In response to lower heat input, the convective / precipitation process shortened. In response to lower levels of UV (dramatically lower) the Thermospheric temperature dropped and most likely ozone formation dropped too.
This all changes the ‘race condition’ between water warmth and stratospheric heat dumping. More Infrared and visible light is reaching the surface of the oceans. That means more absorbed in the surface layer to evaporate water. Less UV means less is reaching deeper parts of the ocean to warm the depths. We ought to have less subsurface heat trying to get out of the oceans. Fewer warm pools. More cool surfaces. The ENSO cycle will tend to more cold states and fewer warm states.
And it is my assertion we could measure all this activity ‘net-net’ via looking at the height of the tropopause.
But WHY doesn’t radiation matter in the Troposphere?
It can’t all just be due to a lot of convection and rain, can it?
Well, ‘yes and no’…
We’ve all had the experience of being out on a ‘cold clear night’ and having felt the heat radiating off to space. Especially easy to feel in the desert. And that is your first clue. Under a midwestern cloudy sky on a muggy summer evening, you don’t get much relief. Not until some rains come. When there is enough water, it is water vapor and clouds that dominate. Over most of the planet, there’s always enough water. 70% of the surface (or so) IS water. On land, lots of that has water too. Either in lakes, streams, and snow; or as damp leaves of vegetation. The few places that are not dominated by water stand out as ‘special’. Deserts and “Mediterranean” climate zones. California is one of those. We get cold on summer nights.
“Why” is pretty simple. We have cold water ‘up wind’ of us here in California. That squeezes the water out of the air. Deserts are worse. Nevada gets our already dry air and lifts it up high (wringing a bit more water out on the mountains as snow) and giving Nevada a “high cold desert”.
In some places, that equatorial lifted and dried air has to come back down. At the edge of that equatorial band. Where that air descends, we get a band of desert. Just run a line around the globe and you get deserts at the two latitude bands each side of the tropics. (Where the air lifted in the equatorial zone comes back down, dried by being rained out during the rise.) Chile in South America. Mojave in the north. Sahara in North Africa. Namib and Kalahari deserts in southern Africa. Gobi in China, the ‘outback’ in Australia. It takes two things. The right latitude for those descending dry air flows, and distance from water dampened air. Not far enough from water, you get a ‘Mediterranean’ climate instead. (Found, not surprisingly, right next to the deserts in California, Chile, Australia, The Mediterranean, etc. etc… right next to the water…)
So our first clue is that ‘water matters’.
In the stratosphere there is very little water.
From that tropopause wiki:
It is also possible to define the tropopause in terms of chemical composition. For example, the lower stratosphere has much higher ozone concentrations than the upper troposphere, but much lower water vapor concentrations, so appropriate cutoffs can be used.
In essence, when in a dry desert or frozen arctic, and feeling that radiative heat loss, you are getting a small sample of the Stratospheric regime. THE place where radiation really matters. Since the deserts are a very minor part of the planet surface, they do not dominate our heat gain / loss profile. Since the polar regions are only really tropospheric part of the year, and have poor insolation most of the year, they don’t dominate our heat gain, but do have a lot to do with our heat loss. And it is very clear that the troposphere is the place where convection and the water cycle control things. They fiercely dominate and can be directly observed in the tropopause height and changes.
This movie shows the movement of the tropical water vapor dominated zone as the sun track moves and the related cloud cover changes. The desert zones show up very nicely on the cloud cover movie.
Why This Chart Doesn’t Matter
And that is why this, often waved about and touted, graph is just irrelevant:
Look carefully at that graph. Notice all those dips and dives, the “CO2 blocked” band and all the rest? Notice that bright green line with the 3.39 W/M^2 added radiative blocking?
Looks pretty grim, doesn’t it. We’re going to be blocking up that radiative window by 3 Watts and slightly shifting the atmospheric transmissivity of that CO2 region. Oh The Horrors!
Now read the title across the top. “Modtran”. It’s a computed model. NOT measured heat flow at that level. “20 km”. It is for a fixed height. From the tropopause wiki:
The troposphere is one of the lowest layers of the Earth’s atmosphere; it is located right above the planetary boundary layer, and is the layer in which most weather phenomena take place. The troposphere extends upwards from right above the boundary layer, and ranges in height from an average of 9 km (5.6 mi; 30,000 ft) at the poles, to 17 km (11 mi; 56,000 ft) at the Equator.
The difference between 20 km and 17 km, especially at the equator where there is a lot of ‘overshoot’ going on from thunderstorms, is just not very significant. The bulk of the air density is in the lower dozen km and that’s where the bulk of the absorbing is going on.
In essence, they are mostly computing the radiation transmissivity of the Troposphere where convection and the water cycle are moving the heat. Where any net change in radiation will be compensated for by more convection, more water transport, a higher tropopause, or any / all of the above. Changing the CO2 transmissivity profile of a band of thunderstorms is just not relevant. It might cause some deserts to be a bit less cold at night, but won’t do anything at all for a polar winter.
Why no impact on a polar winter?
Because the Stratosphere RADIATES the heat away and the stratosphere is just about at the ground in a polar winter and without any water vapor in the way to close that part of the spectral window.
The original of this image is from some paper linked to by the discussion of things here:
It goes on at some great length about how Green House Gases increase the radiative cooling of the Stratosphere. They are throughly convinced that stratospheric cooling is the Evil Twin of tropospheric warming, showing that GHGs are critical to both (so by implication, cooling in the stratosphere endorses warming troposphere). Completely missing the point that the troposphere is dominated by water and convection, so more heat in just means faster transport up. Yet the graph is useful and the discussion is interesting.
The caption reads:
3. Stratospheric cooling rates: The picture shows how water, cabon dioxide and ozone contribute to longwave cooling in the stratosphere. Colours from blue through red, yellow and to green show increasing cooling, grey areas show warming of the stratosphere. The tropopause is shown as dotted line (the troposphere below and the stratosphere above). For CO2 it is obvious that there is no cooling in the troposphere, but a strong cooling effect in the stratosphere. Ozone, on the other hand, cools the upper stratosphere but warms the lower stratosphere. Figure from: Clough and Iacono, JGR, 1995; adapted from the SPARC Website. Please click to enlarge! (60 K)
First, look at that left hand lower edge. See that big red spot? That’s water, dumping heat like crazy at the top of the troposphere. At a height that is determined NOT by that nice flat dashed line of tropopause, but directly by the amount of heat that needs to be dumped! Once again we have a ‘static scored’ model in a dynamic real world. More heat at the surface means more and stronger convection, more and stronger evaporation, and a bigger red spot higher up that graph! Remember that tropical storm “overshoot”? Not seeing it on this graph, are we?… Surges of heat would lead to surges of water across that dotted tropopause line and into the lower stratosphere. That is what we know actually happens.
Now look over at that large orange / yellow / green “cats eye” in the stratosphere that is the CO2 signature. Look directly below it. See that basically empty band of light blue? That is a direct reading on CO2, and it shows that the CO2 is just not doing anything that matters in the troposphere.
From that point, as you move to the right below the tropopause, you find water once again radiating at height, but not as much, in an even larger wavenumber (shorter wavelength). The overall message of this graph is just that in the troposphere, water is everything and CO2 is nothing. We can also add to this graph that convection and evaporation / condensation are major processes in the troposphere and this radiative model isn’t really all that important for surface cooling at all.
In the stratosphere we see some cooling from water vapor, so, little as there is up there, it still does something. However, THE largest blobs of cooling color come from CO2 and ozone. Adding CO2 to the atmosphere causes more radiative heat loss from just those parts of the atmosphere that do radiative heat loss, and does nearly nothing in that part of the atmosphere dominated by convection and evaporation / precipitation. Warming of the surface of the earth increases convection, evaporation, and water transport, and deposits that water and heat higher in the sky; so will dump more heat into the stratosphere (and perhaps more water vapor too … enhancing that water radiative part).
In short, the system is dynamic and has a convection driven lower layer, with a radiative driven upper layer. More CO2 means more radiative heat loss, not less. THAT is why the stratosphere has been cooling (though the upper atmosphere has dropped more on the loss of UV in the solar funk.)
During this solar downturn, the loss of UV overall, and loss of penetrating UV at the ocean surface, has resulted in a lower atmospheric height, and dropping sea temperatures. Soon to show up in lower land surface temperatures. (The snow last year was bad. It will get worse.) Eventually we will re-equilibrate with lower sea temperatures, lower evaporation rates, and lower precipitation rates, with a lower tropopause height. AFTER we dump the last 30 years worth of warm cycle ocean heat.
Along the way, a very cold stratosphere, dropping down the winter Polar Vortex, will cause a fairly strong warm / cold range between poles and the equator. That will cause a ‘loopy jet stream’ as the blobs of cold arctic air slide south and plenty of winter storms as the equatorial heat heads north. Only running down when we’ve cooled the tropics enough to balance the colder poles.
Eventually the sun will wake up again, and enter a new high activity phase. Probably about 20 years on. Then the whole cycle will reverse. More UV, so deeper ocean warming. Gradually building to a warm ENSO cycle and warmer air temperatures. Lots of added tropical storms until the poles ‘catch up’. Warming stratosphere (so a warming polar vortex) as added UV makes more warming aloft. That cycle will continue until the poles ‘warm up again’. Likely in about 50 years.
Odds and Ends
These are some links and bits of information that I found useful, but didn’t fit into the narrative above. Perhaps due to the flow, or sometimes just due to running out of time. I’ve put then here for reference material.
Has a nice description of the Tropopause. Has a nice picture of how the height changes with latitude too, that we saw above. Tainted only by the use of annual averages instead of showing the dynamic range at the poles. I particularly like this very dynamic picture of the TropoBands nature of the Troposphere:
One can clearly see the tropical band where Willis‘ Thunderstorm Thermostat operates. At the other extreme, the polar band where cold air descends from the stratosphere after radiative cooling. In between, the dry descending zone where deserts form after tropical heat was radiated to the stratosphere; and the zone where polar air meets zonal air and makes ‘interesting weather’. ;-) The place where tropospheric water vapor and CO2 get mixed into the stratosphere. We also have the two jet streams seen in static cross section. That’s where the sideways motion happens. When we have a meridional flow (instead of a zonal flow) those jets make more dynamic changes to total mixing area and total length of the descending air mass lines. I think ‘that matters’ to total heat flow…
An interesting quote:
On the other hand, colder regions have a lower tropopause, obviously because convective overturning is limited there, due to the negative radiation balance at the surface. In fact, convection is very rare in polar regions; most of the tropospheric mixing at middle and high latitudes is forced by frontal systems in which uplift is forced rather than spontaneous (convective). This explains the paradox that tropopause temperatures are lowest where the surface temperatures are highest.
This, too, tends to confirm the convection driven tropics and the more placid polar regions dominated by descending air.
Also covers stratospheric cooling.
I have a ‘riff’ on why the lower atmosphere doesn’t radiate effectively that will have to wait. I’ve spent 2 days on this so far and it’s time for dinner… but I’ll do another posting on that topic. It was what started me on the path that lead to this post, and the one from yesterday:
so it’s been a long and complicated couple of days, but worth it, I think. As a ‘clue’: The basic idea is that pressure broadening and fluorescent quenching prevent effective atmospheric radiation in the lower atmosphere. That is why dew forms on metal surfaces in a cold night, but doesn’t just make frozen fog in the air… It involves a bit of quantum physics, but not too much, and some gas dynamics… but just enough that I can’t put it in here in a hour… so gets to wait. Tomorrow, or perhaps after dinner. At this point it is mostly just ‘backing matter’ to the established convecting behaviour of the troposphere.
UPDATE: 12 Dec 2012
In the discussion in comments the topic of heat flow across the tropopause has come up. Again with the bias of ‘static scored radiative model’. I found these three graphs useful for understanding the nature of the tropopause. I picked them up from this article:
The key thing to notice about them is that at about 15,000 meters the temperature hits a minimum (the tropopause) AND the wind speeds hit a maximum ( about 85 knts ) with slower on each ‘side’ of elevation. I just have to think that the conductive and heat flow across a friction layer with 80 knts in the middle and 30 knts just above it will be fairly strong… While the flow will be less vertical and more laminar, it still has a fair enough amount of vertical component to allow for plenty of ‘mixing’ and heat transfer across that band. Though I’m still not seeing much need for it. Mostly you need poleward heat flow, not vertical, moving heat from tropical excess to polar deficit.
Again what we see missing from this kind of chart is the variation from equator to pole. That matters. Yes, this is useful information, for ‘mid latitude’ thinking. But remember to ‘unbias the vision’ and imagine those 80 knt forces headed toward the land surface at the 10,000 foot ( 3,000 M ) average elevation of the Antarctic Plateau … That is where the heat leaves the earth surface and where the fulcrum is set.
So that’s where AGW has got it wrong. It fails to distinguish between stratospheric as the radiative regime and tropospheric as the convective evaporative regime. It fails to use a ‘dynamic scoring’ that recognizes the changing location of the tropopause based on heat flux as driver. It fails to recognize the hysteresis bound regime based nature of heat flow in a very dynamic, non-radiative troposphere. And, most importantly, it fails to recognize that closing an already closed tropospheric CO2 window does nothing that matters. Water is the active agent below the tropopause, and even here it is not as radiative BLOCK to cooling, but as evaporative transport doing cooling, and as the radiative couple to the lower stratosphere.
More heat doesn’t make a radiative driven runaway greenhouse in the troposphere. It makes a faster running heat pipe moving water vapor to the base of the stratosphere and a faster heat loss from the stratosphere.
In short, they forgot to identify what actually happens before they made their ‘mental model’ and played with it.