What is a Watt??? - Printable Version
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What is a Watt??? - Derek - 01-12-2011 06:07 AM
Over on this thread Richard T Fowler kindly took the time to correct me in my understanding of what a Watt means.
I doubt I am the only one to have had, or am still having problems getting to grips with what a Watt actually is.
I have attached to this post a pdf copy of the discussion as it happened, and I hope it helps others.
Please feel free to ask any questions arising, you won't look any sillier than I already have..
Am I embarrassed? Should I be embarrassed?
Well, no, it is not that I was wrong, it is that I have learnt from it.
I may even be able to answer some (simple) questions,
but more likely others will be able to answer them.
RE: What is a Watt??? - Richard T. Fowler - 01-12-2011 06:29 AM
I appreciate your acknowledgment, and I'm glad to have been of service to you and your readers.
Watts are easy. Just remember, a watt is not a watt-second. Watts are power, watt-seconds are energy. A watt-second = 1 joule. And a joule does NOT equal a watt.
If anyone is still confused, it may perhaps be that they haven't understood the difference between power and energy. I think you, Derek, have understood it. But you sometimes get tripped up in considering that a watt = a joule-per-second, and you seem to have sometimes thought that this somehow makes watts interchangable with joules. But they are not interchangable. They are both SI units, which measure different things. On one level, you have always understood that. On another level, the practical level, you have sometimes confused them, which in turn led to the confusion over whether seconds should be included in the measurement of total incoming radiation.
An additional source of confusion is when we speak of "radiation", it is possible to mean EITHER power OR energy, and one has to use the context of the discussion to discern what we're talking about. I think that those who have worked such problems in the past tend to assume that others automatically know whether the discussion is about power or energy. (In this case, it was about power, but even if one knew that, one could still be confused by the fact that, since we are speaking of an *average* power for a period of time, the average power varies directly with total energy.)
Happy thinking, then! On to the next question ....
RE: What is a Watt??? - Derek - 01-12-2011 12:00 PM
(01-12-2011 06:29 AM)Richard T. Fowler Wrote: An additional source of confusion is when we speak of "radiation", it is possible to mean EITHER power OR energy, and
I wonder if another penny has just dropped.
I thought "We" had been talking about "radiation" in relation to the Global Energy Flow W m-2 K&T type plots,
as commonly referred to as Global energy budgets. I assumed we were talking about energy flows.
In the case of the P equation, I would assume now Watts is used in the context of power.
A seemingly small but actually quite important difference.
RE: What is a Watt??? - Richard T. Fowler - 01-13-2011 07:17 AM
A FEW EQUATIONS
Richard, my genuine apologies, in that I deleted the content of this post completely unintentionally.
Now restored as Post 7 below - Thank you SST.
Thanks in advance
RE: What is a Watt??? - Richard111 - 01-14-2011 07:03 AM
Phew! A hard lesson. I am a novice with the physics and the practical meaning of the different terms used in the subject of climatology (if that is the correct term?).
My attempt to understand energy can be seen in this Post in the thread MELTING GLACIERS.
There I attempt to calculate the energy needed to melt enough landborne ice in ten years to raise global sea levels by 1 metre. I don't believe it is possible but then my understanding and calculations are newly aquired and may lack understanding of some critical point.
Meanwhile, for those of us still way down in the learning curve may I offer:
Heat Transfer, Conduction, Convection and Radiation by Nasif Nahle.
RE: What is a Watt??? - Sunsettommy - 01-14-2011 10:41 AM
Quote:Confusion of watts, watt-hours, and watts per hourThe terms power and energy are frequently confused. Power is the rate at which energy is generated and consumed.For example, when a light bulb with a power rating of 100W is turned on for one hour, the energy used is 100 watt-hours (W•h), 0.1 kilowatt-hour, or 360 kJ. This same amount of energy would light a 40-watt bulb for 2.5 hours, or a 50-watt bulb for 2 hours. A power station would be rated in multiples of watts, but its annual energy sales would be in multiples of watt-hours. A kilowatt-hour is the amount of energy equivalent to a steady power of 1 kilowatt running for 1 hour, or 3.6 MJ.
Red bolding mine
RE: What is a Watt??? - Richard T. Fowler - 01-15-2011 11:47 AM
Thought you might want to know, you've just been accused of what amounts to scientific fraud over at the Air Vent page where we met.
The question is over a matter that is in the Johnson work, Computational Blackbody Radiation. Johnson allegedly claims that he is using the diameter of the Earth to compute the disc-equivalent surface area, but he is plugging in "diameter" in the value where radius is supposed to go.
ScienceofDoom is claiming that you were just joshing everyone by pretending to believe that this was correct. He is implicitly saying that you knew it wasn't, all along.
I thought I saw a link to a copy of that here on your forum somewhere. I'll have to go look for it now.
RE: What is a Watt??? - Richard T. Fowler - 01-24-2011 07:31 PM
A FEW EQUATIONS
Equation #1. Watts = "joules per second" = "power".
This is a rate of INTRODUCTION of energy into a certain defined volume of space. (Or, conversely, a rate of its REMOVAL from such a volume.)
To introduce energy into a defined volume of space from outside that defined volume, the energy has to EITHER pass through the boundary of the volume, OR be created within that volume.
For problems that involve only the transport of existing energy, the only introduction of energy is by its passing through the boundary of the volume from outside the volume.
Since the boundary consists of a finite, positive number of planes, the entire boundary has an outer surface area S[a] that can be likened to a single plane of the same area S[a] on ONE of its sides.
"Watts per square meter" = ["joules per second" per square meter] = "density of power".
Joules = "energy".
"Joules per CUBIC meter" = "density of energy".
THOUGHTS ABOUT THESE EQUATIONS
"Density of energy" contains a reference to "Cubic" rather than "Square" because ... why??
Because a joule has a nonzero volume and thus cannot exist within/on a planar surface.
"Density of power" contains a reference to "Square" rather than "Cubic" because when we are not considering newly created energy, power (for example, a watt) has a ZERO volume and thus cannot exist OUTSIDE of a planar surface.
Question: Based on the above truths, can one introduce "energy" into a defined volume of space, from outside that defined volume, in 0 (zero) seconds of time? No, it takes time, because ... why??
Because the energy (joules, or joule, or fraction of a joule) has to be moved through space in order to introduce it into a defined volume of space.
If it could happen instantaneously, then by definition, there would be no space between the starting point and the ending point of the energy. Consequently, the starting point would by definition be part of the defined volume, a reality which we have already specified by definition NOT to be true. Therefore, the answer to the question is "No."
CONCLUSIONS TO BE DRAWN FROM THE ABOVE
A plane (whether flat or curved) can constitute a defined volume of space, but it cannot constitute a NONZERO defined volume. The volume of a plane must, by definition, be zero. Saying it has a volume but the volume is "zero" has the same effect as saying it has "no volume"; thus, we can see that a plane can simultaneously have "a volume" and "no volume", because the word "volume" can mean two different things simultaneously. But at no time can a plane have a nonzero volume.
Units of "Energy" (i.e. just joules, without any spatial reference) are a measurement of a specific amount of energy which exists in a NONSPECIFIC, NONZERO volume of space, such that, by "nonspecific", we mean that the expression of the amount of space containing the specified energy is capable of variation, without affecting the total amount of energy being specified.
Units of "density of energy" are a measurement of a specific amount OR AN AVERAGE AMOUNT of energy which exists in a SPECIFIC nonzero volume of space, such that, by "specific . . . volume of space" we mean "not capable of variation in its volume".
Based on Conclusion #3,
-- If a specific amount of energy A[e] exists within an UNFIXED, nonzero space named N, and
-- if A[e] constitutes the entire energy within N at any time, and
-- if N is redefined to include a larger volume than it did before the redefinition, and
-- if N is thereby enlarged without allowing any of the energy A[e] to exit N either before or after the redefinition, and
-- if the space that is added to N by the redefinition contained no energy prior to the instant of the redefinition, and
-- if no energy crosses into N from outside of N at any time,
THEN: the value of A[e] (the total amount of energy within N at any time) is unchanged during the redefinition, and the expression of the density of energy of N DECREASES at the time of redefinition.
A given rate of power can EXIST for a NONZERO volume of 3-dimensional space, but only for a ZERO length of time.
A given rate of power can PERSIST for a NONZERO length of time, but only where the power is CONSTANT throughout that entire length of time.
Such an expression of persistent power could (but does not necessarily HAVE to) constitute an AVERAGE power, i.e. an AVERAGE rate of energy INTRODUCTION per unit of time, OVER a certain TOTAL period of time.
(Such total period for which the average is expressed can be of KNOWN or UNKNOWN length, and need not be equal to 1 of the specified unit of time in the denominator of the rate.)
Within 3-dimensional space, a quantity of energy can only exist along ALL THREE dimensions of space, AND either 1) the dimension of time AND a timeless dimension of intensity ("density of power"); OR 2) a time-containing dimension of intensity ("density of energy").
Density of energy for a given region of space can be calculated using only the energy that exists within the defined space at the start of the time for which energy is measured; OR just the energy that is introduced/removed DURING the time for which energy is measured; OR the combination of the first two quantities.
Based on Conclusion #7, for a given, fixed, nonzero volume of space AND a given density of power, energy varies directly with time.
Based on Conclusion #7, for a given, fixed nonzero volume of space AND a given OVERALL power, energy varies directly with time.
Based on Conclusion #7, for a given, fixed, nonzero volume of space, a given OVERALL power, AND a given density of ENERGY, overall energy varies directly with time. QUESTION: "RTF, how can density of energy be constant, while overall energy is variable?" Aha, the answer is ........ when your "density of energy" is an AVERAGE density of energy OVER a period of time!
RE: What is a Watt??? - Derek - 01-25-2011 02:33 PM
Richard T Fowlers A FEW EQUATIONS post is going to take some digesting.
I will also whilst doing so refer in greater depth to,
" Table 4. Examples of SI derived units whose names and symbols include SI derived units with special names and symbols "
" heat flux density, irradiance.....watt per square meter.....W/m2 "
RE: What is a Watt??? - Derek - 01-28-2011 12:05 AM
I have now had a second read through RTF's A FEW EQUATIONS post it has cleared (at least part of) the subject (area) up for me.
However I will add "I think" as Richard111 did.
So, "we" now have (a unique approach and actually quite clear) description of a W/m2 as a unit of power, thank you RTF.
I will not revisit the SI links above just yet, because as RTF as I (think I) now "get" states,
"A watt is power. Not energy, power.
It is power because it does NOT contain time.
The time has been removed by dividing the joule a/k/a the watt-second (which DOES contain 1 second worth of time) by 1 second.
Because the amount of time in the numerator is of equal value to the amount of time in the denominator, ALL time is removed, and
we are left with a timeless unit of power.
Although a W/m2 is a "derived" unit of a Watt, I have no issue with the above also applying to the W/m2 unit.
My seemingly stubborn "reluctance" to understand RTF's correct descriptions of what a W/m2 is,
is because I have been looking at this from an "in context" point of view.
The context being with regard to computer climate modeling, and the K&T type plots.
Until recently very few have actually used the word power when referring to W/m2 in this context,
and the K&T plots are confusingly titled as "Energy Flows".
Power and energy seem to have been used (or misunderstood as used) interchangeably and incorrectly by many a lot of the time,
or / and my understanding of what was being said was incorrect.
I very much doubt I was alone in this (but I will be one of the very few to admit it openly).
However many that do understand that a Watt is a unit of power,
may have been coming at "the problem" with computer climate modeling and of the K&T type plots from this angle.
" I think that the key difference is that the models are all assuming that the entire system is in equilibrium.
As long as that is the case, power is all you need to compare incoming radiation.
But as soon as you assume that equilibrium is not the only state (and possibly never realized),
then you have to deal with energy in order to compare different geometries. "
RTF I have deliberately highlighted part of the above quote in red, is it possible for you to expand upon / explain this more please.
I think this is a main / major point many have missed the importance and subtly of.
The NASA plot does seem to "assume" an equilibrium, so does seem to be describing using W/m2 as power.
At so many levels (in context of computer climate modeling and the K&T type plots specifically) any assumption of "equilibrium" to my mind is a misnomer,
it simply can not and does not happen.
This is a whole "different" subject area as such (there is no "equilibrium" as depicted / assumed), but
I think it reasonable and have been taking it as read that there is no "equilibrium". It is a silly notion.
So, I have been looking at these K&T type plots as energy flows, that is the "source" of my "reluctance" regarding what is a W/m2 actually describing.
The plots should be describing Joules because there is no equilibrium,
the only way the figures quoted make sense at present (realizing there is no "equilibrium) is that
they must be actually W/m2 per second figures, ie, Joules.
Hence I have used the below plot as an "opposite" of the NASA version.
I knowingly chose the above two plots because of their confusing depictions in regard to the K&T types of plots in respect to this discussion of what is a W/m2 because
they can not show an "equilibrium" as such,
because then there would be no man made "global warming" would there. ?
For the depicted "net absorbed" to have an effect, and there be warming (or cooling), it must also be released at a later time (at no doubt varying rates)
- this I assume must introduce time into the plot. Hence I describe this plot as "opposite" to the NASA plot, which "avoids" this issue.
Do the the above types of plots depict a "second" energy version, of the first, never given, "natural equilibrium" power version,
that man by his activities has supposedly unbalanced, so resulting in the "second" energy versions we see depicted above.
NB - Claes Johnson may be suggesting (as I superficially understand his works) the power figures are wrong within the K&T type plots because
they must first (but do not) take the "temperature" (energy level) differences between emitter and receiver into account, and so
the powers will be quite different to those currently depicted.
Below is a slightly altered by Claes Johnson version of one of the K&T type plots
in which he illustrates the above point I have tried to make regarding his approach.
RE: What is a Watt??? - Derek - 01-29-2011 12:08 AM
I have spotted this posted by SST elsewhere in the forum,
which must apply at so many levels to the computer climate models and K&T "types" of plots, and also
any (possibly persisting) notions of a depicted "equilibrium",
incorrectly employing the W/m2 unit of power.
" You can not average an intensive property and have it mean anything. "
Sunsettommy posted in,
RE: What is a Watt??? - Derek - 01-29-2011 04:18 AM
Whilst looking into the subtle and confusing differences between heat flow density and intensity that it occurs to me is happening in
the SI and Wiki definitions / explanations of the physics that are associated with the term W/m2 as applied to the K&T type plots, and
therefore by default the computer climate models I have come across the following Wikipedia page and figure.
" This figure is a simplified, schematic representation of the flows of energy between space, the atmosphere, and the Earth's surface, and shows how these flows combine to trap heat near the surface and create the greenhouse effect. Energy exchanges are expressed in watts per square meter (W/m2) and derived from Kiehl & Trenberth (1997).
The sun is responsible for virtually all energy that reaches the Earth's surface. Direct overhead sunlight at the top of the atmosphere provides 1366 W/m2; however, geometric effects and reflective surfaces limit the light which is absorbed at the typical location to an annual average of ~235 W/m2. If this were the total heat received at the surface, then, neglecting changes in albedo, the Earth's surface would be expected to have an average temperature of -18 °C (Lashof 1989). Instead, the Earth's atmosphere recycles heat coming from the surface and delivers an additional 324 W/m2, which results in an average surface temperature of roughly +14 °C .
Of the surface heat captured by the atmosphere, more than 75% can be attributed to the action of greenhouse gases that absorb thermal radiation emitted by the Earth's surface. The atmosphere in turn transfers the energy it receives both into space (38%) and back to the Earth's surface (62%), where the amount transferred in each direction depends on the thermal and density structure of the atmosphere.
This process by which energy is recycled in the atmosphere to warm the Earth's surface is known as the greenhouse effect and is an essential piece of Earth's climate. Under stable conditions, the total amount of energy entering the system from solar radiation will exactly balance the amount being radiated into space, thus allowing the Earth to maintain a constant average temperature over time. However, recent measurements indicate that the Earth is presently absorbing 0.85 ± 0.15 W/m2 more than it emits into space (Hansen et al. 2005). An overwhelming majority of climate scientists believe that this asymmetry in the flow of energy has been significantly increased by human emissions of greenhouse gases . "
I also came across this figure, on this Wikipedia page, which "says" much the same thing.
Given the subject of this thread, when taken IN CONTEXT,
the confused and confusing use of the term W/m2, the incorrect use of the unit of power, and the incorrect use / apparent "interchangeability" of power and energy,
as well as now mentioning / adding density and intensity,
then the source of the confusion seems rather clear to me.
The K&T type plots, the "greenhouse effect" they depict, and computer climate modeling. ie, Anthropogenic (man made - literally) Global Warming pseudo science.
AND, finally for this week,
Sunsettommy has posted the below in the charts thread, post 145.
Alan Siddons has produced the plots from the view point of accepting that W/m2 is correctly used as a unit of power in the K&T type plots,
and then proceeds to show how ridiculous (and unphysical) they actually are.
Given my approach has been to show that the W/m2 unit of power is used incorrectly, then this is a nice contrary approach / view,
to the problems of computer climate modeling and the K&T type plots, as well as the "greenhouse effect" I have been trying to expand upon.
This I have been trying to do by asking the question what is meant and described by the use of W/m2 in the context of the K&T type plots, computer climate modeling, and
the as explained by AGW (that it is wholely dependent upon) so called greenhouse effect "theory"..
These were from Alan Siddons:
This one converts W/m² to temperatures (in Celsius) to show how stupid the whole budget is.
Notice how radiation from the 1.8 degree atmosphere raises the surface, which was initially at minus 39.8, to 14.8 degrees! That's impossible.
The next one is meant to illustrate that you cannot send light of a certain intensity through
a series of reflections, absorptions and re-emissions and expect that it will end up BRIGHTER than it started.
Again, K-T violates all known laws of physics.
End of quote.
RE: What is a Watt??? - Derek - 02-06-2011 05:42 AM
From this thread,
(02-01-2011 02:39 AM)Richard111 Wrote:(01-17-2011 03:37 PM)Sunsettommy Wrote: People who are truly into discussing the topic will be able to talk about what is known and what needs to be better understood.No need to prove who is more correct since the objective is to learn.To better understand what is being postulated.The presentation under discussion may be incorrect or has room for improvement.But talking about it will benefit all parties to the discussion.
I replied there,
(02-01-2011 01:33 PM)Derek Wrote: Richard111, I will have to use your quote of Sunsettomy's comment regarding discussion above in the small explanatory piece I have yet to write.
"the small explanatory piece I have yet to write." is not so small now, and as yet unfinished.
I hope you all understand that the " small explanatory piece " comes first for me at present.
Then I will tidy up these threads.
As a "reminder" does anyone have a copy of RTF's "A FEW EQUATIONS" post please.
RE: What is a Watt??? - Derek - 04-22-2011 12:36 PM
Elsewhere I have been following discussions in regards of whether it is correct or not to divide solar input received at the top of the atmosphere by 2 or 4.
I think this is an absolutely central issue, that must be understood.
On this thread so far, the casual reader can not have failed to notice the "pain" I have suffered in trying to understand what a W/m2 actually is.
My confusion is because of the way W/m2 is used in the K&T plots.
I hope that may have become apparent to at least some whilst reading the thread.
I shall try to explain what has been confusing me in regards to the way W/m2 has been used in K&T.
As far as physics is concerned, W/m2 is a power figure, derived from a Watt AND
as such it is a timeless figure. ie, it must apply across all time scales.
This later point has, I think, been missed by many.
So, when using W/m2 figures the physics of what is being described must be taken into account in determining what maths can be used.
ie, the physics determines the maths.
If W/m2 is used in a way that is not physically correct, then it is the maths determining the physics, which will not work in reality.
The maths may be wonderful, but if it ain't physical, it is worthless maths.
My maths is particularly weak, I have no issue admitting that, but, I do remember vividly one maths lesson.
My maths teacher at school went purple with rage trying to explain to a classroom of not particularly interested teenage boys,
with regards to algebra, that you can not compare lions and zebras..
They have to be the same, you must use a common denominator.
With regard to W/m2, the only "common denominator" is that the figure must describe the physics in such a way as to be a timeless figure.
Otherwise comparison is not correct or possible.
The sun permanently illuminates half of the sphere that is planet earth.
So, as a hemisphere is twice the area of a disc, then dividing the power of solar input received by 2 over a lit hemisphere is correct.
The physics of dividing solar P received by 2 for planet earth is found in reality.
If however we divide solar P received by 4 then we have to assume that the planet has rotated fully once, or "x" number of times, (or the planet is disc shaped...)
because the solar input has been spread over the entire sphere's surface.
(A sphere has 4 times the area of a disc, and twice that of a hemisphere.)
This has introduced a time element to W/m2, in this case 24 hours, or multiples thereof.
P/2 = lion.
P/4 = zebra.
When P/2 and P/4 are used we are not using the same "thing", infact according to the definition of what a W/m2 actually is,
then because P/4 introduces a time element to a timeless figure, then,
whatever the figure is, it is not a W/m2.
The K&T plots start off with 342 W/m2 solar input, which is a P/4 figure.
From there on in, almost all the figures used in the plots are of different time scales,
some are timeless, as they should be, figures, some are not.
We are comparing lions, zebras, monkeys, giraffes, and goodness knows what other animals all together on one plot.
My maths teacher would probably of exploded, if he had ever looked at a K&T plot.....
When physically incorrect figures are used, or net figures are used, then the physics are mangled and any resemblance to reality is lost completely.
Maths does not determine the physics,
maths can ONLY describe the physics when applied in the correct physical manner to a given situation.
In K&t, and computer climate models the maths determines (mangles) the physics...
Net figures are a major problem also because, there could be, let us say,
16 arrows / reasons in one direction, and 6 or 7 arrows / reasons in the other direction.
Using a net figure would just mangle the physics, and any relationships within the physics.
Furthermore the net arrows will probably give the wrong impression of how it might change due to other factors changing.
In short, there are so many ways that the physics have to be described correctly by the maths, that,
the "sum" overall is probably impossible.
On thing is for certain though, calculating physics determined by maths is not the right way to go about things,
infact, it is a crassly stupid approach doomed to failure.
The best example of which is dividing solar input power to planet earth by 4.
RE: What is a Watt??? - Richard111 - 04-23-2011 05:22 AM
Sympathise with the math Derek. All I had at school were four figure log tables and a slide rule. It was embarrassing how long it took me to work out how to do antilogs on my on board computer.
I am trying to follow the excellent maths explanations by Joseph E. Postma at this site here.
You can download Understanding the Thermodynamic Atmosphere Effect in pdf format.
If it wasn't for the atmosphere and all the stuff in it we would be living on a rather overheated desert type world. Hmm.. have you read Dune? No sky dragon but he had sand dragons.
RE: What is a Watt??? - Derek - 05-29-2011 05:22 AM
A quick post holiday "update".
A W/m2 is a power figure, or if you prefer a "pressure" figure,
it is a temperature signal.
Years ago an Uncle of mine whilst explaining electricity to me, used a water pipe simile.
He said, imagine pipes carrying water rather than electricity.
Volts is the pressure, and amps is the pipe diameter.
You can not work much out about the flow of water or electricity without knowing the pressure (voltage) and the diameter of the pipe (amps).
This all makes sense to me as a simple analogy to "visualise" electricity flows.
W/m2 is a pressure figure, therefore it assumes the objects being compared are the same size / mass, etc, if they are not,
then another figure for "diameter" is needed.
How can so many have missed "diameter" of the pipes involved is missing from K&T and "greenhouse" ???????
"Greenhouse" is taught as,
1) Solar input received at earth's surface = 239W/m2.
2) 239 W/m2 is radiated by the earth's surface.
3) The atmosphere is heated up to the same temperature and thus radiates up and down 239W./m2.
So, the earth radiates from the atmosphere 239 W/m2 as it should to space, ie, earth appears to be -18C when viewed from space, as it should be,
the earth's surface is 239W/m2 from the sun, AND 239W/m2 from the atmosphere, 478W/m2 = +15C*.
So, "greenhouse" is taught as "pressure" only, but, if one includes amount of energy, or "diameter",
then earth's surface only receives 1 (directly from the sun) at 239 W/m2 + 1/2 ("back radiated" from the atmosphere) at 239 W/m2,
which is too little for earth's surface, according to "GH" to be 15C.
Earth should only radiate half the amount of energy it receives, at 239 W/m2 from the sun to space...
According to "GH" "theory".
* = 15C is a very questionable and often quoted supposed "Global Mean Temperature" (GMT),
That IS NOT the earth's surface temperature.
The 15C as quoted so frequently, is infact a near surface air temperature, as measured (usually at about 6 foot above the actual surface), and statistically produced by dubious methods.
Which is a different thing completely to earth's actual surface temperature.
The actual surface temperature, or any attempt at a meaningful global mean of it,
is infact completely absent from such descriptions.
RE: What is a Watt??? - Richard111 - 05-29-2011 06:20 AM
Yes! Very good point. Me, being a simple trusting soul, assume they always meant the "blackbody" equivalent of 1 square metre for each level of radiation defined in watts per square metre.
I have several times asked the question how to you define the radiation from a VOLUME of the atmosphere? I am currently trying to learn about infrared detectors as used in the satelites. So far it is not encouraging. The best I've read about so far only record IR from 4 microns to 20 microns. Big deal! There is still IR radiation down to 1,000 microns! It also appears they "average" all the readings. For example they will see high intensity narrow band (8 to 12 microns) through the 10 micron atmospheric window. They will also see low intensity wide band radiation from the cloud tops (most of which will be missed due to cutoff at 20 microns in the measuring instrument) and then there will be the very low intensity 15 micron radiation from CO2 in the cold upper troposphere where water vapour does not exist in any great quantity.
All of that is somehow added together to show -18C (255K) radiation from the whole earth from a source claimed to be radiating at 240 watts per square metre.
I know all the sums add up but verifying the input parameters seems fraught.
RE: What is a Watt??? - Derek - 05-29-2011 07:41 AM
(05-29-2011 06:20 AM)Richard111 Wrote: Yes! Very good point. Me, being a simple trusting soul, assume they always meant the "blackbody" equivalent of 1 square metre for each level of radiation defined in watts per square metre.
The use of the W/m2 figure / unit ASSUMES
the same mass, "size", emissivity, specific heat value, etc, etc, etc,
between emitter and receiver..
Which in K&T, and "greenhouse" means,
Quack, quack, oooops.
RE: What is a Watt??? - Sunsettommy - 05-29-2011 10:33 AM
(01-13-2011 07:17 AM)Richard T. Fowler Wrote: A FEW EQUATIONS
It is restored and found at post #7.
RE: What is a Watt??? - Derek - 05-29-2011 01:40 PM
Thank you SST.