Bill Bob
Topic Author
Posts: 49
Joined: Sat Apr 07, 2001 9:54 pm

Lapse Rate Question

Tue Jul 24, 2001 7:04 am

Please forgive my spelling i not from your country. Can explain what is adiabatic lapse rate? And how hi it goes up? Is it the same on both sdes of the equater? do it go up to trop.? thank you. I lke to read wether and some day fly above clouds to.
Posts: 192
Joined: Sun Feb 27, 2000 3:07 pm

RE: Lapse Rate Question

Tue Jul 24, 2001 3:37 pm

All I could find was what was called the dry adiabatic lapse rate(DALR). Strait from my Jeppeson Aviation Wheather Book. It is a little confusing, but from what I got it is a tool used to figure atmosphere stability. I am going to try to explain what the book is telling me as simple as possible.
The DALR is a sloping line from the suface running through all of the atmosphere layers. The slope is -3 deg C per 1000 ft gain in altitude. Then we compare that to the actual Lapse rate NOT the ISA Lapse Rate. From that we can determine the stabilty of the atmosphere.
When the Lapse rate is greater than the DALR we have unstable conditions. When the lapse rate is equal to the DALR the conditons are neutral. Finally when the Lapse Rate is less than the DALR the conditions are stable.
This applies world wide in all atmosphere layers
Good luck and happy flying
Bill Bob
Topic Author
Posts: 49
Joined: Sat Apr 07, 2001 9:54 pm

RE: Lapse Rate Question

Wed Jul 25, 2001 2:30 am

Ok thankyou, does the 3 dagree loss of temperatuer continue how far up? I think I read it stops at bottom of troposphere and higher than that ther is no further rreducton of temperatuer. Bill Bob
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Joined: Sun Feb 27, 2000 3:07 pm

RE: Lapse Rate Question

Wed Jul 25, 2001 5:34 am

Actually, It is the standard lapse rate that actually stops at the trop. Then at the Stratosphere the air temperature starts to climb as one climbs. Then in the mesosphere ( around 150 thousand ft.) then temp falls again.

The DALR is just an imaginary line figured out by metorlogists and physicists to help us pilots figure out if our ride is going to be bumpy and help us predict if the wheather is going to be bad.

The DALR is constant up through all of the layers in the atmosphere at the same -3 deg per 1000.

What does stop at the trop is wheather. Except for supercell thunderstorms, cirrus clouds, and winds aloft, their is no wheather activity above the tropopause.

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Joined: Wed May 19, 1999 12:31 am

RE: Lapse Rate Question

Wed Jul 25, 2001 7:12 am

Sorry, but the former is not quite true.
You have 2 different kinds of Adiabatic lapse rates.
The first one is the DALR, which has a rate of -3degrees per 1000ft, and reaches until the temperature is at DEW POINT (which itself will decrease with 0,5deg./1000'). From that point, the DALR changes into the Saturated ALR, and has an original decrease rate of -1,5deg/1000' and as the air becomes dryer, it will increase its lapse rate until becomming back 3 degrees. At this piont, there is no more humidity.To calculate the transition point of DALR to SALR (the Condensation Level) us this simple formula: Heigth= (Temp- Temp dewpoint)*400.

If the ELR, so the Actual Environmental lapse rate is more than -3/1000' , there will be an Absolute Instability.
If the ELR is higher than the SALR but lower than the DALR , so say between 1,5 and 3/1000', there will be a Conditional Instability.
If the ELR is lower than the SALR, there is Absolute Stability.

I could tell you a lot more, but then I would get too deep and technical (like the different types of diagrams,...) but if you are really interested, buy a book like the Jeppeson one, which is very easy to understand, but the in-depth is a bit lacking compared with European ATPL books like Oxford or Four forces.

aaron atp
Posts: 517
Joined: Sun Mar 19, 2000 1:17 pm


Wed Jul 25, 2001 3:22 pm

in addition to the other posts, just realize that adiabatic is a thermodynamics term meaning "no heat transfer," (which means that nothing like a cold body of water is cooling the air immediately above it)

in effect, the cooling is a result of onlythe gas law equations

the heat contained by a mass of air becomes more "spread out" as the pressure decreases and the given volume increases (thus a decrease in density) for an increase in altitude.

with the heat more "spead out" the temperature decreases -thus what we call adiabatic cooling. air with different moisture contents have different specific heat values, and thus different lapse rates, dry/moist/etc.

the rest concerning lapse rates, cloud bases, and stability you already know....


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