2012/01/02

Are Adiabatic Lapse Rates Controlling Temperatures

Better stuff here on adiabatic lapse rates!!
http://scienceofdoom.com/2012/08/12/temperature-profile-in-the-atmosphere-the-lapse-rate/

Some of the rest is interesyting in this post:


Adiabatic Lapse Rates
wiki
Types of lapse rates

There are two types of lapse rate:
 Environmental lapse rate – which refers to the actual change of temperature with altitude for the stationary atmosphere (i.e. the temperature gradient)
 The adiabatic lapse rates – which refer to the change in temperature of a parcel of air as it moves upwards (or downwards) without exchanging heat with its surroundings. The temperature change that occurs within the air parcel reflects the adjusting balance between potential energy and kinetic energy of the molecules of gas that comprise the moving air mass. There are two adiabatic rates:[6] Dry adiabatic lapse rate
 Moist (or saturated) adiabatic lapse rate
http://www4.uwsp.edu/geO/faculty/ritter/geog101/textbook/atmospheric_moisture/lapse_rates_1.html
In "The Atmosphere" we discovered that air temperature usually decreases with an increase in elevation through the troposphere. The decrease in temperature with elevation is called the environmental lapse rate of temperature or normal lapse rate of temperature. Recall that  the normal lapse rate of temperature is the average lapse rate of temperature of .65o C / 100 meters. The environmental lapse rate of temperature is the actual vertical change in temperature on any given day and can be greater or less than .65o C / 100 meters.  Also recall that the decrease in temperature with height is caused by increasing distance from the source of energy that heats the air, the Earth's surface. Air is warmer near the surface because it's closer to its source of heat. The further away from the surface, the cooler the air will be. It's like standing next to a fire, the closer you are the warmer you'll feel. Temperature change caused by an exchange of heat between two bodies is called diabatic temperature change. There is another very important way to change the temperature of air called adiabatic temperature change.
 http://daphne.palomar.edu/jthorngren/adiabatic_processes.htm
Make sure you notice that we are talking about moving air (rising or subsiding),  not still air.  The change in temperature of still air (that is, air that is not rising or subsiding) follows the Environmental Lapse  Rate, which varies considerably, but averages about 6.5 deg C/1000 meters  (3.6 deg/1000 feet).  In still air, if you went up in a hot air balloon, carrying a thermometer and taking the air temperature every 1000 meters, on average the temperature would drop 6.5 degrees C every 1000 meters.  The rate of temperature change as you rise in still air is not as great as the rate of change of rising air; that is, the air parcel does not cool off as fast.
For instance, the air temperature at sea level is 28 degrees C.  Climb into your balloon, release the tethers, and go up 1000 meters in the still air.  On average, the air temperature 1000 meters up will be _21.5___degrees C.   If the air were rising, and the temperature at sea level was 28 degrees C, what would the temperature of the air be after it rose 1000 meters? 18C
http://www.sci.uidaho.edu/scripter/geog100/lect/05-atmos-water-wx/05-part-7-atmos-lifting-fronts/ch5-part-7a-atmos-liftin.htm
http://www.geographypages.co.uk/lapse.htm
http://www.st-andrews.ac.uk/~dib2/climate/lapserates.html
People talk of adiabatit lapse rates as if they control the atmosperic temperatre. Why?
These lapse rates refer to moving a number of molecules from low pressure to high pressure and getting heated. No problem with that. BUT
For every molecule moved down to high press ure there must be a molecule moved from high to low. It cannot be a one way transport (obviously!).
So, in my books, the heating effect of falling molecules equals the cooling effect of rising molecules. Hence no effect.
So Why is it colder up a mountain than on the plains.
GHG free air absorbs litle of the available sunlight. Air with GHGs absorbs only at the known absoption frequencies and the proportion of theses frequencies in the TSI is relatively small. There is therefore little air heating due to sunlight.
However sunlight hits the ground and 70% gets absorbed and reradiated as heat at long wave infra red frequencies. These will heat the air via absoption. There is more close ground creating warming in a valley than on a hill hence it will be warmer.
NOW if there is a 1000 metre plateau will this be as warm as the valley below - if not, why not?

from WUWT
The adiabatic lapse rate is defined by the "gas Laws" not by gravity (other than of course high gravity gives high pressure!).
The adiabatic lapse rate requires that a fixed number of molecules be moved between pressure differences. Once at a new pressure the new temperature will stabilise to the surroundings (but that is not what adiabatic lapse rate is about).
However, for every molecule transported from high to low pressure there MUST be a molecule transported from low to high pressure. This means there is NO net flow of energy.
Where the atmosphere blends into a vacuum there can be no convective/conductive transfer of energy (there is nothing to transfer the energy to!)
Radiation is the only option. N2 H2 O2 etc. have little propensity to absorb radiation. Hoever they will get warm by transfer of heat from GH gasses. All hot bodies emit radiation (bb radiation).

At the other end of the air column you have similar problems. The ground/sea warms through absorption of the shorter wavelengths of TSI (where most of the solar energy is). The heat is radiated from the ground/sea as LWIR and by contact at the boundary between earth and atmosphere. The heat must be transferred from molecule to molecule by contact or by convection. A slow process. Conduction will be enhanced by high pressure, convection will be slowed.
The radiated energy is NOT significantly absorbed by O2 N2 H2 etc. no matter what the pressure. Even a solid glass fibre can be made extremely low loss 0.2dB per km and the molecules are pretty solidly packed http://www.fiberoptics4sale.com/wordpress/optical-fiber-loss-and-attenuation/ . Without a GHG this radiation would escape without attenuation straight to space. GHGs will "absorb" this LWIR at certain frequencies and re-emit it in all directions. The time for this energy to be "reabsorbed" in another molecule is dependent on the path length which is dependent on the proximity of other GHG molecules which is dependant on the pressure of the atmosphere.
The time taken for the radiation to bounce from molecule to molecule increases the time it takes for the energy to travel from ground to space.
The energy input to the system is at a constant rate. Slow down the output and the system gets hotter. A hotter system will radiate more energy (BB radiation).
Where does the energy from static pressure difference come in to this?









Atmospheric longwave irradiance uncertainty: Pyrgeometers compared to an absolute sky-scanning radiometer, atmospheric emitted radiance interferometer, and radiative transfer model calculations.


================
Downward longwave irradiance uncertainty under arctic atmospheres: Measurements and modeling
http://www.slf.ch/ueber/mitarbeiter/homepages/marty/publications/Marty2003_IPASRCII_JGR.pdf
Figure 2

Spectral and Broadband Longwave Downwelling Radiative Fluxes, Cloud Radiative

Forcing, and Fractional Cloud Cover over the South Pole
http://www.webpages.uidaho.edu/~vonw/pubs/TownEtAl_2005.pdf


Measurement of night time downward radiation
So we know the solar output received in the dark is 0
We know that O2 and N2 have very very very little thermal radiation.
So where does all that downward radiation come from (at least 270W/sqm)
It can only be from GHGs.
During the day we receive about 380W/sqm
So the 270W/sqm is additional to the solar irradiance.
So the average night day temp difference is less than expected (no sideways conduction/wind required)
N2 O2 absoptions are mainly rotational and thereefore mainly in the microwave region. There is not a great amount of radiation in these frequencies.

Cloud transmission (from above-FTIR looking down) from
An introduction to atmospheric radiation
By Kuo-Nan Liou




Transmission through the atmosphere. If GH effect exists then there should be mmissing parts of emission spectrum when looking at the earth. AND when looking up at the sky there should be higher levels of radiation at the same wavelengt as is missing when looking down. Is this the case? It seems so:


spectral plot is here:
http://www.patarnott.com/atms749/powerpoint/ch6_GP.ppt

IR great plains measured here:
SGP Central Facility, Ponca City, OK
36° 36' 18.0" N, 97° 29' 6.0" W
Altitude: 320 meters
http://www.arm.gov/sites/sgp

Better stuff here!!
http://scienceofdoom.com/2012/08/12/temperature-profile-in-the-atmosphere-the-lapse-rate/


5 comments:

  1. See my response to one part of your statement at Science of Doom, reproduced here for interest:

    You said:

    "..Also, to maintain number of molecules at each altitude what goes up must come down! So energy transfer is minimal (zero).."

    If higher temperature molecules move up and lower temperature molecules move down you have conservation of mass. And you have conservation of energy.

    But you don't have constant energy vs height.

    In fact, what happens when convection takes place - say with a heated plate at the bottom of a water tank - is that warmer water moves up and colder water moves down.

    This redistributes energy.

    Here is a nice page with video link showing an experiment on this topic. There are other great videos via links at the top of this page. It accompanies the excellent Marshall & Plumb (2008) textbook.

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  2. Thanks for that .... BUT!!
    at 10k metres the temp is set by the lapse rate and the temp at 0m
    so a parcel of air moving from 0 to 10km will loose thermal energy and gain potential enregy ending up at the same temp as the other stuff at 10km

    an in reverse from 10km to 0m so unless you assume that the parcel is heated without heating the other parcels no heat will be transported..

    I assumed that if a 100% insulated row of air were suddenly turned to a column of air then the lower air would be compressed and heated and the upper rarified air would cool to maintain energy balance.( low air high T but low potential energy; high air low T but high potential energy) This would give the adiabatic lapse rate. But then will not the air mix to eventually give a uniform temperature? But then you have medium temp with high potential energy and medium temp with low potential energy. Thi9s seems wrong?

    Also I know you have said that N2 and O2 do not emit radiation but what is the difference between a gas and a solid when it comes tho blackbody radiation. - Most books talk about all matter above 0K emitting BBradiation. So why not non GHGs. I KNOW that no narrow emissions from non-GHGs will occur - non is captured and none is emitted. But non GHGs can be warm, they are matter, so do the not radiate over the usual BB spectrum?

    I just cannot find and definitive statement that says gasses do not have a black body radiation!


    of interest:
    http://www.ssec.wisc.edu/library/coursefiles/03_abs_emiss_ref.pdf

    The physics of atmospheres By John Theodore Houghton
    preview:
    http://books.google.co.uk/books?id=K9wGHim2DXwC&printsec=frontcover&dq=%22The+physics+of+atmospheres+By+John+Theodore+Houghton%22&hl=en&sa=X&ei=eeEHT9LGMseo8QPrlayJCA&ved=0CDUQuwUwAA#v=onepage&q=%22The%20physics%20of%20atmospheres%20By%20John%20Theodore%20Houghton%22&f=false

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  3. TFP,
    Here's how I think it works. The lapse rate is the point of neutral convective stability. Below that, it's stable; above, it's unstable.

    At the dry lapse, a rising parcel of air heats at exactly the same rate as still air nearby. It neither gains nor loses buoyancy.

    But below the lapse rate it's stable. As it rises, it cools relative to air nearby. It takes energy to push it up. That energy comes from the KE of the atmosphere - eddies etc.

    And where does the energy go? It does work pumping heat against the temp gradient. The rising air carries "coolness" up.

    What about the displaced air? Same. Imagine 1kg rising, 1 kg coming down. The falling air now warms faster than nearby air. It takes work to force it down. And it is carrying heat against a thermal gradient. Again heat pumping. The rising air carries coolness up - falling brings warmth down.

    The effectiveness of this heat pump is proportional to deviation from lapse rate. And it pumps heat to maintain the lapse rate. It all comes from the KE of the air, which is driven by temp differentials (Hadley cells etc).

    Conversely, above the lapse rate, everything is the other way around. Rising air becomes warmer than the ambient, so rises even faster. It carries heat down the gradient and creates KE. It is a heat engine. And because of that, it tends to reduce the gradient - accelerated conduction. So just as the pump brought the gradient up to 10 K/km, the engine brings it down. Again the effectiveness is proportional to the deviation of the gradient from 10.

    As to non-GHG gases, all substances have an emissivity. With gases it is very selective (bands), and there's no such thing as a black body. They emit according to emissivity and mass. Monatomic and symmetric diatomic gases have very low emissivity.

    ReplyDelete
  4. Nick
    The easy bit first
    I can find no definitive statement about black/grey body radiation from gases. All books say BB radiation occurs from all "stuff" above 0K temperature. Everyone scientific agrees with this. but what is the difference between solid and gaseous stuff. E.G. take solid CO2. I would assume this does BBradiation as the temp is above 0K. This heats a bit and sublimates to CO2 gas. Now all of a sudden it only radiates at certain frequencies - why?

    Liquid nitrogen is similar. I assume BBradiation when a liquid(?) but then on turning to gas NO radiation will be emitted. Just does not sound logical!


    Lapse rates - I just have to think about!

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