Storm Australian Severe Weather Forum

Severe Weather Discussion => General Weather - all topics not current severe weather. => Topic started by: Mike on 12 January 2007, 12:29:13 PM

Title: Lapse Rates and Skew T Aerological Diagrams
Post by: Mike on 12 January 2007, 12:29:13 PM

Could you clarify 'lapse rate' please.  I'm understanding where your'e going but are you referring to the time taken for droplets to rise or fall within any given latitude within the storm?

And where do i find the CAPE rate on a Skew-T graph? Is on the right hand side where the Mb are?

Sorry to be a burden, but it's education you see.

Title: RE: Lapse Rates and Skew T Aerological Diagrams
Post by: Jimmy Deguara on 12 January 2007, 12:47:08 PM

Lapse rates refer to the difference in temperature from one pressure level to another. Commonly used lapse rates are 850hPa - 700hPa levels and 700hPa - 500hPa. Obviously in a 'standard atmosphere, you would anticipate temperatures to drop as you climb into the atmosphere. But if for whatever reasoning - it may be colder aloft or perhaps warmer below than normal, then this leads to steepening of lapse rates (or gradient). The steeper the lapse rates the more potentially unstable the atmosphere is.

But now we have to consider typical values. Remember though, lapse rates vary based on dry air compared to saturated air.

Rather than re-invent the wheel, I have quoted from this website which goes into depth on instability:

http://www.piercecollege.edu/offices/weather/stability.html     by Steve W. Woodruff

Quote

We have covered DALR, ELR, and SALR, now let's add one more: Dew Point Lapse Rate. Again, the exact rate varies depending on atmospheric conditions, but the range is relatively small nevertheless. NOAA meteorologist, Thomas Schlatter, performed numerous calculations of dew point lapse rate under various conditions and found that values range from 1.6ºC/1km to nearly 1.9ºC/1km.

Let's refer to dew point lapse rate simply as DPLR. Okay, quick recap before we move on:
DALR = dry adiabatic lapse rate = 9.8ºC/1km
SALR = saturated adiabatic lapse rate = 3.9ºC/1km - 7.2ºC/1km
ELR = varies from place to place and from time to time...
DPLR = 1.6ºC/1km - 1.9ºC/1km

I hope this helps as a simple explanation.

Regards,

Jimmy Deguara

Title: Re: Lapse Rates
Post by: Paul Graham on 12 January 2007, 12:59:03 PM

Hi Mike,

The 'lapse rate' is the observed temperature drop with increasing altitude that results from the vertical pressure gradient matching the earth's gravitational pull and treating the atmosphere as an ideal gas.  By the ideal gas equation, the air temperature is proportional to the pressure so that a drop in pressure will cause a proportional drop in the temperature, ie. pv=nRT where p:pressure, v:volume, n:number of moles, R:Avogadro's constant, T:temperature (this is from memory, correct me if I'm wrong).    

Cheers,

Paul

Title: Re: Lapse Rates and Skew T Aerological Diagrams
Post by: Paul Graham on 12 January 2007, 01:00:25 PM

It's incredible what's been added to Wiki - it's all there!  Take a look at: http://en.wikipedia.org/wiki/Hydrostatic_equilibrium
http://en.wikipedia.org/wiki/Lapse_rate