A paper published August 20th in Geophysical Research Letters finds from newly deployed observation systems that the Southern Oceans show an annual net heat loss of -10 Wm-2.
Key Points
- Southern Ocean air-sea fluxes are under-observed, leading to large uncertainty
- The first year-long air-sea flux observations quantify an annual cycle
- Shows seasonal cycle, small annual net ocean heat loss and extreme events
Due to a previous “paucity of reference observations”, this paper is the first to study annual heat flux between the atmosphere and the Southern Oceans, a “key component of the global climate system: insulating the Antarctic polar region from the subtropics, transferring climate signals throughout the world’s oceans and forming the southern component of the global overturning circulation.”
That finding contradicts claims that the oceans are gaining ‘missing heat’ due to an increase in greenhouse gases. For example, The figure below from Bob Tisdale compares the ARGO-era Ocean Heat Content observations to the model projection, which is an extension of the linear trend determined by Hansen et al (2005), for the period of 1993 to 2003. Over that period, the modeled OHC rose at 0.6 watt-years per year. With the recent seasonal declines in Global Ocean Heat Content anomalies, the model projection is rising at a rate that’s more than 10 times higher than the observations since 2003. 10 times higher. Yet the southern ocean has just been demonstrated to be losing heat.
Here is the paper:
First air-sea flux mooring measurements in the Southern Ocean
GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L16606, 8 PP., 2012
doi:10.1029/2012GL052290 E. W. Schulz, S. A. Josey, and R. Verein
The Southern Ocean is a key component of the global climate system: insulating the Antarctic polar region from the subtropics, transferring climate signals throughout the world’s oceans and forming the southern component of the global overturning circulation. However, the air-sea fluxes that drive these processes are severely under-observed due to the harsh and remote location. This paucity of reference observations has resulted in large uncertainties in ship-based, numerical weather prediction, satellite and derived flux products. Here, we report observations from the Southern Ocean Flux Station (SOFS); the first successful air-sea flux mooring deployment in this ocean. The mooring was deployed at 47°S, 142°E for March 2010 to March 2011 and returned measurements of near surface meteorological variables and radiative components of the heat exchange. These observations enable the first accurate quantification of the annual cycle of net air-sea heat exchange and wind stress from a Southern Ocean location. They reveal a high degree of variability in the net heat flux with extreme turbulent heat loss events, reaching −470 Wm−2 in the daily mean, associated with cold air flowing from higher southern latitudes. The observed annual mean net air-sea heat flux is a small net ocean heat loss of −10 Wm−2, with seasonal extrema of 139 Wm−2 in January and −79 Wm−2 in July. The novel observations made with the SOFS mooring provide a key point of reference for addressing the high level of uncertainty that currently exists in Southern Ocean air-sea flux datasets.
Here are two additional figures from the paper: wind speed
Surface variables and heat flux:
h/t to The Hockey Schtick
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Stephen says: “Tim is trying to salvage his position by emphasising the theoretical likelihood of a process that isn’t much different to zero.”
No, I am trying to prevent the propagation of a few specific errors. For instance, when you categorically say I am “incorrect” when in fact I am correct (based on standard definitions of “net air-sea heat flux”). OR when you conclude ”
In truth, we are not that far apart in our positions. I suspect we agree that (for an annual average over the earth)
* Sunlight is the biggest form of energy flux into the oceans
* Evaporation is the biggest form of energy flux out of the oceans
* Conduction is a much smaller form of energy flux out of the oceans (maybe 1/5 or 1/8 as much as evaporation).
* Thermal IR (composed of a large upward flux and a smaller downward flux) is a net energy flux out of the oceans.
From what I recall from other previous discussions, our main disagreement deals with the effect of increased GHGs. I think that more GHGs will produce mroe downward IR, which will increase the evaporation rate by increasing the surface temperature of the ocean slightly. I believe you feel the evaporation rate will go up with on increase in surface temperature (but I could be wrong).
Gail,
I agree with many of the facts and graphs you presented. Let me make a couple quick points.
“The wavelength from 10 to 20um (where the majority of the energy from the earth is radiated) passes through the atmosphere esp. if the amount of H2O vapor is small.”
1) even if the “majority” passes through, there is still some IR that gets absorbed. The air in turn can radiate IR in various directions including downward.
2) Clouds are nearly perfect blackbodies. Thermal IR energy from the surface gets blocked almost 100% by the clouds. The clouds in turn radiate very efficiently back to the surface.
All together, the downward IR flux from GHGs and clouds is certainly less than the upward energy, but the downward energy is a large fraction of the upward thermal IR from the surface. The air returns some of the energy back to the surface — no magic needed.
“Therefore the air does toss energy to space.”
Yes, but it also “tosses: energy back to the surface.
“However the ocean absorbs its energy from the HIGH END of the solar spectrum and not the air.”
I’m not sure what your point is. The SURFACE of the ocean absorbs energy from IR from GHGs & clouds. The DEEPER layers of the ocean absorb energy from the “HIGH END of the solar spectrum” The entire spectrum eventually gets absorbed by the ocean. The entire spectrum contributes to the heating of the ocean.
“The air itself might “warm” the ocean but it is by a very negligible amount.”
I guess that depends on your definition of “negligible”. Everything else being equal, the atmosphere (including water vapor & clouds) returns enough energy to warm the earth several degrees (33 C by some estimates) — I would hardly call that “negligible”.
Tim Folkerts says:
August 23, 2012 at 9:20 am
Lars says: “Positive into the oceans, negative outside”
The graph says: ” (positive is out of the ocean, negative in to the ocean)”
….. If you meant the NET longwave flux was always OUTWARD, then I agree.
(Much of the rest of what you say I agree with, like the existence of a cool skin layer of the ocean and only shortwave EM energy being able to penetrate beyond a thin layer at the top.)
——————————————————————————–
Tim yes, I expressed myself badly wrong in the line, however good that you got the meaning.
We both agree that heat transfer cannot happen from the surface of the ocean to the deeper layers as long as there is a cool skin, which means that any warming coming from greenhouse stops at the skin layer.
If the skin layer is getting warmer in average only then we can start talking about possible influence of the GHG everything else staying the same.
I would say that this could make an interesting lab experiment, however have not seen such.
The conclusion from what we say above is that it is wrong to try to make any direct connection between greenhouse gas energy and ocean heat content in terms of energy transfer.
The exchange between atmosphere and ocean happens only at the skin layer.
If there are any changes in the skin layer temperature, then, only then, eventually the ocean may retain more heat from the sun.
The global sea surface temperature are known and measured:
http://bobtisdale.wordpress.com/2012/08/06/july-2012-sea-surface-temperature-sst-anomaly-update/
The variations show very little warming which may be attributed to other factors like less clouds or small increase in solar radiation (if we compute ACRIM composite and not PMOS) and would point to a very small climate sensitivity to CO2.
This keeping in mind that all the heat from CO2 and all GHG are blocked at the skin layer, and not going down in the ocean.
Lars.
Thanks for your contribution.
I have previously tried to tell them over at a warmist site that only if the temperature gradient through the cool skin layer declines could there be any effect on the ocean bulk from downward IR.
There has been no evidence produced to that effect.
Since that cooler skin layer is caused by evaporation plus radiation removing energy faster than it can be brought up from below it follows that more evaporation would intensify that cool layer and not dissipate it.
Thus the extra downward IR from more CO2 (if any) cannot warm the ocean bulk.
[snip – embedded advertising link in an otherwise relevant comment ]
[snip – embedded advertising link in an otherwise relevant comment ]
“Thus the extra downward IR from more CO2 (if any) cannot warm the ocean bulk.”
You seem to be saying that extra 10 W/m^2 of extra IR will lead ONLY to increased evaporation, but not to ANY warming of the surface of the ocean. Am I right?
By that logic, you would say that a decrease of -10 W/m^2 should not lead to cooling, but only to decreased evaporation. Am I right?
But what if we decrease the downward IR by -80 W/m^2. Your logic would say there is STILL no cooling, but evaporation would have to stop (since there is only ~ 80 W/m^2 of evaporation from the oceans). So we would have water at the SAME temperature as now, with NO evaporation!
No, what would happen instead if we cut the incoming IR by 80 W/m^2 is that evaporation would decrease somewhat (perhaps by 60 W/m^2) and the outgoing IR would also decrease (say by 20 W/m^2) so that the total change would equal the change in the incoming IR. But to decrease the outgoing IR, the surface temperature would have to drop.
So I agree that MUCH of the increased IR would simply go into speeding up the water cycle, but SOME of it must go into warming the surface of the oceans.
Evaporation cannot stop under an open sky with air movement because that movement keeps humidity below 100%.
There is a basic minimum rate of evaporation which is independent of downward IR.That is set by solar input plus pressure at the surface.
ALL downward IR onto a water surface adds to evaporation provided humidity is less than 100% and ALL is used up by the phase change.Taking the Earth as a whole humidity is on average always way below 100%.
If any area gets closer to 100% then windiness increases and more vapour is whisked upward or laterally.
Here is an example as to how the numbers work:
i) The basic rate of evaporation removes, say, 10 units of energy from the water every minute.
ii) Meanwhile, at some precise moment, 5 units of IR hit the surface.
iii) 1 unit has enough time to provoke extra evaporation but then, instantly, because the enthalpy of vapourisation is 5 to 1, the phase change soaks up the rest of the 5 units of downward IR with no effect on the basic rate of 10 units of energy removed from the water per minute.
iv) There doesn’t even need to be a surface temperature change because all of those 5 units go straight to latent heat which does not register on thermometers.
vi) The gradient of temperature within the cooler ocean skin changes not at all and the bulk ocean temperature is unchanged.
Tim Folkerts:”So I agree that MUCH of the increased IR would simply go into speeding up the water cycle, but SOME of it must go into warming the surface of the oceans.”
I have a hard time understanding the logic here. If the surface of the ocean is cooler than both the sub-surface water and the air above it, doesn’t this imply that there can be no net transfer of heat into the surface water. Is your point simply that the surface cools less when the air above it is warmer?
Cheers, 🙂
“ALL downward IR onto a water surface adds to evaporation … There doesn’t even need to be a surface temperature change …
But you still miss the logic fallacy of your argument. If ANY increase in IR ONLY increases evaporation with no surface temperature increase, then ANY decrease in IR ONLY decreases evaporation, with no decrease in temperature. But downward IR is WAY more (~ 300 W/m^2) than evaporation (~ 100 W/m^2). So if IR decreases by 100 W/m^2, then, by your logic, we would stop evaporation without any other change in surface temperature!
Shawnhet asks: “I have a hard time understanding the logic here. If the surface of the ocean is cooler than both the sub-surface water and the air above it, doesn’t this imply that there can be no net transfer of heat into the surface water. Is your point simply that the surface cools less when the air above it is warmer?”
A good question! The answer requires understanding the total balance of heat. Let’s think about the surface skin layer and the subsurface bulk oceans as two different systems.
1) There IS a transfer of energy into the subsurface from sunlight.
2) There is no transfer out of the subsurface by evaporation or thermal IR (both are blocked by the skin layer).
3) The method of cooling the subsurface to maintain an approximate equilibrium must then be by conduction thru the skin layer.
4) To conduct thermal energy thru the skin layer, the top of the skin layer must be cooler than the bottom of the skin layer (as is indeed observed) (the top of the skin layer is cooled by conduction to the air, thermal IR and evaporation)..
5) Conduction depends on the temperature gradient. If the top of the skin layer is heated (say by an electric heater or IR light), then the gradient decreases, and the conduction upward thru the skin layer decrease.
6) If the downward sunlight stays the same, but the upward conduction decreases, then there must be a NET transfer into the oceans.
Of course, this all assumes that thermal IR actually can warm (or cool) the surface. If Stephen Wilde is correct that evaporation rates can be increased without changing the wind, surface pressure, humidity or surface temperature, then (5) would be wrong and the argument would fall apart.
“But downward IR is WAY more (~ 300 W/m^2) than evaporation (~ 100 W/m^2). So if IR decreases by 100 W/m^2, then, by your logic, we would stop evaporation without any other change in surface temperature!”
I don’t accept the standard AGW view of downward IR. I think it is just the temperature of the air molecules just above the surface.The warmer they are the more evaporation there will be and at standard atmospheric pressure plus current levels of insolation the temperature of the air molecules above the surface is equivalent to what would be produced if there were a radiator in the sky giving off 300 W/m2
At standard atmospheric pressure and current levels of insolation that air temperature at the surface happens to produce a background rate of evaporation with the energy value of 100 W/m2.
Assuming those suspiciously round numbers are accurate.
So if the molecules near the surface do become a bit warmer, say rising to the equivalent energy value of a radiator in the sky producing 305 W/m2 then 1 of the extra units will provoke more evaporation and the other 4 will be instantly mopped up too.
The background evaporative flow from the water to the air will still be at 100 W/m2 so the warmer air has failed to warm the ocean bulk at all.
This is where we get into the contentious issue of atmospheric pressure but that is for another day.
I could never reach agreement on this issue with someone who thinks there actually is a radiator floating about somewhere in the sky.
“If Stephen Wilde is correct that evaporation rates can be increased without changing the wind, surface pressure, humidity or surface temperature”
Not what I said. Changes in windspeed, surface pressure and humidity do change (indeed the entire global air circulation changes albeit imperceptibly from human emissions) so as to facilitate a fast enough evaporative response to either prevent a surface temperature increase altogether or eliminate it over time averaged around the planet.
We have to be careful about the term surface temperature because I concede that it will change locally or regionally when the air circulation reconfigures in order to maintain balance between solar energy in and longwave out. I prefer to say that the system energy content remains much the same over time.
“This is where we get into the contentious issue of atmospheric pressure but that is for another day.”
It may help if I make a brief comment.
Atmospheric pressure at the ocean surface sets the energy value of the enthalpy of vapourisation. At 1 standard atmosphere the ratio is 5 to 1.
That gives us the energy cost of a given amount of evaporation so unless one changes atmospheric pressure that energy cost per unit of evaporation stays the same.
The fact is that at 1 standard atmosphere at current levels of insolation and the current landmass distribution the energy cost of a given amount of evaporation from the oceans requires an air temperature above the surface equivalent to a radiator in the sky producing 300 W/m2 to produce 100 W/m2 of evaporation.
You can increase or decrease the temperature of the air or of the oceans by whatever means you like but if the water surface remains exposed to the open sky then the energy cost of a given amount of evaporation stays the same if atmospheric pressure remainds at 1 standard atmosphere.
If the air is warmer than the water then the warmer air causes more evaporation but because the air is warmer the evaporative process takes the extra energy from the warmer air until it comes down to the water temperature.
If the air is colder than the water then less evaporation occurs but when it does occur the evaporative process takes the extra energy it needs from the water until it comes down to the air temperature.
So the evaporative process, taking the energy it needs from whichever medium air or water is best able to supply it, imposes an automatic negative system response to warming or cooling of either air or water.
Anything that warms the air causes a faster loss of energy from the air to reduce the warming of the air.
Anything that cools the air causes a faster loss of energy from the water to the air to reduce the cooling of the air.
Anything that warms the oceans causes a faster loss of energy to the air to reduce the warming of the oceans.
Anything that cools the oceans causes a slower loss of energy from oceans to air to reduce the cooling of the oceans.
In practice these changes translate into global air circulation changes until solar energy once more matches longwave energy out.
That is how climate variations occur and the atmospheric response involves changes in the vertical temperature profile of the atmosphere and the latitudinal positioning of the jets and climate zones.
One of the phenomena that the system never produces is warmer air producing more evaporation but the evaporative process taking the extra energy it needs from the water before the air has come down to the temperature of the water.
AGW theory relies on the happening of that impossibility because unless CO2 warms the oceans first it cannot warm the air.
In fact it just warms the air and the sea / air interaction then causes an air circulation response that ejects the additional energy to space sooner thus cancelling the warming effect of the CO2.
Slight correction:
Anything that warms the air above the water temperature causes a faster loss of energy from the air to reduce the warming of the air.
Anything that cools the air below the water temperature causes a faster loss of energy from the water to the air to reduce the cooling of the air.
Anything that warms the oceans above the air temperature causes a faster loss of energy to the air to reduce the warming of the oceans.
Anything that cools the oceans below the air temperature causes a slower loss of energy from oceans to air to reduce the cooling of the oceans.
Another correction (doing this too late at night):
“One of the phenomena that the system never produces is warmer air producing more evaporation but the evaporative process taking the extra energy it needs from the water before the air has come down to the temperature of the water.”
should be:
“One of the phenomena that the system never produces is warmer air producing more evaporation but the evaporative process taking insufficient energy for its needs so that there is a surplus left over to warm the water.”
“I don’t accept the standard AGW view of downward IR. I think …
I could never reach agreement on this issue with someone who thinks there actually is a radiator floating about somewhere in the sky.”
Then there is no point in continuing this discussion. You “don’t accept” standard physics, replacing it with your own musings. It is easy to measure downward IR radiating. It is easy to match this downward IR to GHGs and clouds. But you simply choose not to accept this. Instead you hypothesize some vague ‘equivalent of a 300 W/m^2 radiator that is not a radiator’. You actually seem to have a good understanding of much of the science and make some good arguments. But then you seem to choose not to accept specific parts that conflict with your desired conclusion.
If you are comfortable creating your own science — cool — just don’t expect to convince others.
Tim Folkerts:”6) If the downward sunlight stays the same, but the upward conduction decreases, then there must be a NET transfer into the oceans.”
I am not sure that this follows necessarily, unless you ignore the effects of evaporation. Evaporative cooling will recreate a gradient and reduce or eliminate the transfer into the ocean. By my calculations, raising the temp of 1 kg of water at the surface by 1C will require ~4.2 KJ but by Clausius and Clapeyron increasing the temp of the water by that amount will increase evaporation by 6% which will require .06 kg of water to be evaporated which will take ~135KJ. IOW, ~3% of the total flux would go into the ocean, and 97% would go to driving the water cycle faster.
Now, this is overly simplistic I am sure as warming the very top of the ocean will most likely have effects on subsurface (of the ocean) temps. But doesn’t this highlight the fact that you need to include some ideas about how the temperature of the ocean as a whole will behave when exposed to a warmer atmosphere.
Cheers, 🙂
I’ll try one more time to try and explain my point; It is not easy because as far as I know this is a new way of lookng at the issues but I think a more accurate way.
At current atmospheric pressure and level of insolation the system requires certain consequences to enable thermal energy in to match thermal energy out, namely:
i) An average flow of energy from the oceans at the rate of 100 W/m2 PLUS
ii) A temperature of the air at the surface equivalent to the air temperature that would be achieved if there were a radiator in the sky producing 300 W/m2 (the cause is not an actual radiator but the combined effect of pressure and insolation on the temperature of the air molecues at the srface) PLUS
iii) An air circulation configured as it is today so as to ensure that the sea / air energy exchange is just right to support the energy in from the sun / energy out to space balance for the system a a whole.
All three are required to be in balance to achieve the current global system energy content (not temperature because that varies regionally and locally a great deal and does so in 3 dimensions from the bottom of the oceans to the top of the atmosphere)..
The first two are dictated by surface pressure and solar input acting together on the different physical properties of air and water. It is those different physical properties which cause the different thermal responses in air and water to the same pressure and insolation.
The third is controlled by humidity, windiness and slight surface pressure variations around the globe which give rise to adjustments in the rate of evaporation from the oceans. Those slight pressure variatons result in climate zones and jet streams which then serve as the means by which humidity and windiness can vary so as to induce changes in the rate of evaporation.
The slight surface pressure variations are caused in the first instance by the fact that water vapour is lighter than air and so produces convection without any necessary change in temperature.
So, if anything seeks to alter the net rate of energy flow from ocean to air without a change in average global surface pressure or insolation then that will disrupt the system balance such that the energy in from the sun will no longer be matched by energy out to space.
The consequence will be a change in circulation involving humidity and windiness and shifts of the surface pressure distribution in the form of climate zones and jetstreams.If energy out exceeds energy in for any reason the atmosphere shrinks and vice versa. The expansion or shrinkage affects the circulation patterns.
That change in circulation restores the energy in energy out balance and in the process eliminates the thermal effect of whatever force was trying to alter the rate of energy flow from oceans to air.As explained before, the changes in the rate of evaporation will extract the extra energy needed from whiche medium is warmer than it needs to be to support the energy in / energy out balance for the system as a whole.
If the water gets a little too warm so that the upward energy flow exceeds 100 W/m2 then the faster evaporation takes the excess from the water and flings it upward to space faster leaving the energy content of the bulk ocean uchanged.
If the air gets a little too warm so that the energy in the surface air molecules exceeds that 300 W/m2 then the faster evaporation takes the excess from the air and flings it up to space faster without any change in the energy content of the bulk ocean.
Thus is the air circulation as a whole the global thermostat (not just the tropics as per Willis Eschenbach).
Nothing other than changes in surface pressure or insolation will alter the system energy content though there will be changes in surface temperatures whilst the adjustments to the speed of energy flows through the system change in response to nfluences other than changes in pressure or insolation.
The point for AGW theory being that, yes, more human emissions of CO2 would have an effect but the natural effects (from other causes such as global cloudiness and albedo changes caused by top down solar variations and variations in the rate at which the oceans release energy to the air caused by internal ocean cycling) are hugely greater..
In face of those natural forcings our changes in CO2 count for nothing at all in terms of changes in atmospheric circulation.
And in the end the changes of air circulation always succeed in maintaining system stabilty by matching the sea / air energy exchange to support overall system balance where energy in equals energy out.
Otherwise we could not have had liquid oceans for 4 billion years despite huge asteroid impacts and widespread volcanic outbreaks.
Tim Folkerts says:
August 24, 2012 at 12:07 pm
“ALL downward IR onto a water surface adds to evaporation … There doesn’t even need to be a surface temperature change …
But you still miss the logic fallacy of your argument. If ANY increase in IR ONLY increases evaporation with no surface temperature increase, then ANY decrease in IR ONLY decreases evaporation, with no decrease in temperature. But downward IR is WAY more (~ 300 W/m^2) than evaporation (~ 100 W/m^2). So if IR decreases by 100 W/m^2, then, by your logic, we would stop evaporation without any other change in surface temperature!
——————————————
Tim, I have a couple of thoughts experiments for you, can you give me your understanding on these 2 examples?
1) Considering the case downwards IR would not exist (on the moon for instance), we place a rock under the sun at 0°C temperature, wrapped in a surviving foil not to lose heat, would the rock get warmer or not?
To make the case more difficult we place a filter and there is only about 100 W/m2 sun radiation hitting the rock, will it warm up or cool down?
http://en.wikipedia.org/wiki/Space_blanket
2) Considering the case it is night and there is no sun radiation we place the rock still at 0°C on the ground – this time on the earth with average air temperature at the ground at 0°C – wrapped in the same surviving foil, would it get warmed up by the 300W/m2 from the -X°C air above?
Lars proposes a couple thought experiments …
I don’t think your thought experiments are well-posed enough to really give an answer yet.
* Is there any thermal conduction to/from the surrounding air/ground? (Conduction will be important in most real-life situations.)
* is there any IR from the ground? (A rock above the ground would also get “up-radiation” from the ground below/beside unless we block that as well).
* what are the properties of the space blanket? If you have and idealized space blanket that PERFECTLY reflects all photons, then neither external sunlight nor external IR sources would make any difference — only conduction and the initial temperature of the rock would matter. If it only reflects “very well” then it will matter how well it reflects sunlight and how well it reflect thermal IR.
I think the “space blanket” is an unnecessary complication. I think you could pose your scenarios more easily with some other mechanism to focus on the specific issues you want to address.
tjfolkerts says:
August 25, 2012 at 11:57 am
Lars proposes a couple thought experiments …
Tim… Why would you try to avoid the question and focus on small details?
The question to be answered is simple:
Can 300 W/m2 radiation from colder atmosphere be compared with 100 W/m2 radiation from the sun? Are these same kind? Yes or No?
If there is any difference and what is the difference?
I do not propose the exercise to disprove “back radiation” or to say that it has zero influence, but to put it in its right place. 300 Watt from colder object A towards a warmer object B does not increase the temperature of that object B at all. It is no net heat transfer as you seem to consider it.
To my understanding through averaging back radiation and taking it away from the heat transfer process where it occurs we tend to forget what it is. Your sentence : But downward IR is WAY more (~ 300 W/m^2) than evaporation (~ 100 W/m^2)
is in this view very wrong
I don’t think your thought experiments are well-posed enough to really give an answer yet.
* Is there any thermal conduction to/from the surrounding air/ground? (Conduction will be important in most real-life situations.)
No. better consider the surrounding air/ground at 0°C as the rock and as isolated as possible from these
* is there any IR from the ground? (A rock above the ground would also get “up-radiation” from the ground below/beside unless we block that as well).
see above
In my view the exercise is simple, one can take his own rock, measure its temperature and put it in the garden in the night. observing its temperature. One can also point the instrument to the sky and measure downwelling IR. Isolate the rock as much as possible from other temperature exchange, we want to focus now on this source and its influence.
Don’t make the matter more complex, consider the ground at 0°C everywhere or at “rock temperature”.
Make your own assumptions if you don’t like the space blanket.
Then take a different heat source with a very high temperature. A radiator could be also ok – important is to meet the Watts/m2 you measure from downwelling radiation. See what happens. Keep the rock isolated from other heat exchange as much as possible.
* what are the properties of the space blanket? If you have and idealized space blanket that PERFECTLY reflects all photons, then neither external sunlight nor external IR sources would make any difference — only conduction and the initial temperature of the rock would matter. If it only reflects “very well” then it will matter how well it reflects sunlight and how well it reflect thermal IR.
I think the “space blanket” is an unnecessary complication. I think you could pose your scenarios more easily with some other mechanism to focus on the specific issues you want to address.
the space blanket is to isolate on the silver side, so yes silver side on the rock to let it lose as few heat as possible. I understand a space blanket lets lose about 3% and isolates 97% from the silver side.
The idea is to keep the rock isolated as much as possible from heat exchange with any other object in the environment except the energy sources we want to understand:
-1) IR radiation from a colder object
-2) shortwave radiation – or if you prefer IR radiadiation from a warmer object with significant temperature difference, but keep same Watts/m2 or even less
Lars asks :”Tim… Why would you try to avoid the question and focus on small details?
The question to be answered is simple.”
Because all those “small details” will affect the answer to your thought experiment! You are asking about radiation balance, but then you include the space blanket, one of whose main purposes is to block the selfsame radiation!
I’ll work with the principle here:
So in broad strokes …
1A) If we consider “typical surface conditions” with sunshine but no “back-radiation” the sun would provide ~ 160 W/m^2 (averaged over 24 hours). The rock (assumed to have emissivity =1) would have an effective surface temperature of 231 K = (-42 C) (averaged over 24 hours). (Actually, because of the T^4 power-temperature relationship, the average would be lower, but we will ignore those details too). Of course, it would be warmer during the day and cooler at night.
1B) If we consider “blackbody surface conditions” (no sunshine absorbed/reflected by the air; no sunshine reflected by the rock) with sunshine but no “backradiation” the sun would provide ~ 340 W/m^2 (averaged over 24 hours). The rock would have a surface temperature 278 K. (around +5)
1C) By adjusting the albedo and/or absorption by the air, the temperature could be anywhere from -42C to +5C
1D) By decreasing the emissivity, the temperature of the rock would go up from the above numbers.
2A) If we consider “Typical back-radiation” of 333 W/m^2, the rock would have a temperature of about 277 K (~ 4 C) if back-radiation was the only heat source.
2B) On a cloudless night, the back-radiation would be less. Using the calculations from MODTRAN for a cloudless night with “Standard US Atmosphere” the back-radiation would be ~ 259 W/m^2 or 260 K = -13 C
2C) on a cloudy night, the back-radiation would be enhanced. Again using “Standard US Atmosphere” and adding low stratus clouds, the back-radiation would be ~ 362 W/m^2 or 283 K = +10 C.
Obviously by playing with atmospheric condition, we can get a wide variety of answers for the temperature of the rock. None of these numbers is hard to find; none of the calculations are difficult. I would encourage you to do them yourself.