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wrote in
: On 24 Nov 2004 21:38:35 -0800, (Andrew Sarangan) wrote: Adiabatic lapse rate is 1C/1"Hg for moist air (depending on moisture content) and 3C/1"Hg for dry air. 2C/1"Hg is a representative average for somewhat moist but unsaturated air. It is still a useful indicator of stability. I would not discount is as a completely meaningless number. It is a useful reference, just like 29.92" and 15C. Adiabatic lapse rate never changes. It is not a useful indicator of stability. It tells you nothing about stability until you know the actual lapse rate of the air mass in question. You should read up on lapse rates. There is dry adiabatic lapse rate, moist (saturated) adiabatic lapse rate, average adiabatic lapse rate and even more obscure ones like superadiabatic lapse rate and autoconvective lapse rate. It is definitely not a constant, but the commonly accepted average lapse rate is 2C/1000ft. |
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Ah, I see what you are getting at. But I never said stability is only
determined by adiabatic lapse rate. The difference between the environmental lapse rate and the adiabatic lapse rate is what determines the stability. The average adiabatic lapse rate is 2C/1000' but can vary based on moisture. Therefore, if the environmental lapse rate is higher than 2C/1000' that atmosphere can be considered to be unstable. For a moist parcel of air 2C/1000 environmental lapse rate will be unstable, but for a dry parcel of air it will be stable. wrote in : Adiabatic lapse rates (there are more than one) are theoretical and calculated. The calculations do not change from day to day. The dry adiabatic lapse rate witll be calculated tomorrow the same way it is today. It measures a physical process, i.e., the amount of heat given up as air rises and expands, Therefore it does not, as you suggest, indicate stability or instability, since it will be the same in unstable air as it is in stable air. It is the ;lapse rate of the surrounding air that determines stability, not the lapse rate of the rising air, which is the same every day, day in and day out. |
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On 25 Nov 2004 12:02:42 -0600, Andrew Sarangan
wrote: The difference between the environmental lapse rate and the adiabatic lapse rate is what determines the stability Like I said... |
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#17
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"Andrew Sarangan" wrote in message
om... Adiabatic lapse rate is 1C/1"Hg for moist air (depending on moisture content) and 3C/1"Hg for dry air. 2C/1"Hg is a representative average for somewhat moist but unsaturated air. No, moist but unsaturated air has an adiabatic lapse rate of 3 degC (i.e. the unsaturated adiabatic lapse rate). The difference between that and saturated comes not from the amount of water vapor in the air as a mixing of properties, but from the latent heat produced when the water vapor condenses, which only happens when the air becomes saturated. It's not a progression, but a sharp difference when the water vapor starts to condense. Julian Scarfe |
#18
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That's interesting, but I find it strange that moisture content does not change the adiabatic lapse rate. Moist air has a higher heat capacity than dry air, so I would expect the adiabatic lapse rate of moist air (but unsaturated) to be lower than dry air. "Julian Scarfe" wrote in : "Andrew Sarangan" wrote in message om... Adiabatic lapse rate is 1C/1"Hg for moist air (depending on moisture content) and 3C/1"Hg for dry air. 2C/1"Hg is a representative average for somewhat moist but unsaturated air. No, moist but unsaturated air has an adiabatic lapse rate of 3 degC (i.e. the unsaturated adiabatic lapse rate). The difference between that and saturated comes not from the amount of water vapor in the air as a mixing of properties, but from the latent heat produced when the water vapor condenses, which only happens when the air becomes saturated. It's not a progression, but a sharp difference when the water vapor starts to condense. Julian Scarfe |
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"Andrew Sarangan" wrote in message om... "Mike Rapoport" wrote in message link.net... 2C per thousand has nothing to do with stability. In unsaturated air, 2C/1000 is stable. In saturated air 2C/1000 is unstable. 2C/1000 is the standard for calibrating altimeters, it has nothing to do with the real atmosphere or stability. Mike MU-2 Adiabatic lapse rate is 1C/1"Hg for moist air (depending on moisture content) and 3C/1"Hg for dry air. 2C/1"Hg is a representative average for somewhat moist but unsaturated air. It is still a useful indicator of stability. I would not discount is as a completely meaningless number. It is a useful reference, just like 29.92" and 15C. How can 2C/1000' tell you anything about stability? If the air is saturated then 2C/1000 is unstable, absoluteley totally unstable. 2C/1000 in saturated air is likely to be the inside of a thunderstorm. If the air is unsaturated and the lapse rate is 3C/1000, the air is stable, totally stable and smooth. 2C/1000 tells you nothing about stability unless you know whether the air is saturated or not. The only numbers that tell you about stability without knowing the vapor content are lapse rates above 3C/1000 (termed absolutely unstable) or below 1C/1000 (absolutely stable). Any lapse rate between 1C and 3C/1000 is termed "conditionally stable". Please explain how 2C/1000 is used in altimeter calibration. I did not know altimeters had any temperature corrections. Altimeters are preasure guages with a scale in feet. They assume a pressure lapse rate with altitude and the pressure lapse rate that they use is ISA whch assumes 15C at SL and 2C/1000'. Mike MU-2 |
#20
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"Andrew Sarangan" wrote in message 1... Ah, I see what you are getting at. But I never said stability is only determined by adiabatic lapse rate. The difference between the environmental lapse rate and the adiabatic lapse rate is what determines the stability. The average adiabatic lapse rate is 2C/1000' but can vary based on moisture. Therefore, if the environmental lapse rate is higher than 2C/1000' that atmosphere can be considered to be unstable. Absolutely not! If the air is unsaturated and the lapse rate is 2C/1000 but below 3C/1000, then the air is absolutely, totally stable! No "ifs", "ands", or "buts", it is stable. It cannot be considered to be unstable. For a moist parcel of air 2C/1000 environmental lapse rate will be unstable, but for a dry parcel of air it will be stable. Yes! but this is in direct contradiction to your above statement "Therefore, if the environmental lapse rate is higher than 2C/1000' that atmosphere can be considered to be unstable." Mike MU-2 wrote in : Adiabatic lapse rates (there are more than one) are theoretical and calculated. The calculations do not change from day to day. The dry adiabatic lapse rate witll be calculated tomorrow the same way it is today. It measures a physical process, i.e., the amount of heat given up as air rises and expands, Therefore it does not, as you suggest, indicate stability or instability, since it will be the same in unstable air as it is in stable air. It is the ;lapse rate of the surrounding air that determines stability, not the lapse rate of the rising air, which is the same every day, day in and day out. |
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