How saturated adiabatic lapse rate varies with temperature

Following the previous discussion on lapse rate, can anyone point me to
source where I can find out how saturated adiabatic lapse rate varies with
temperature? I know that this number increases from 1C/1000' to 3C/1000' as
the temperature gets colder, but I would like to see a plot or an equation
that describes this behavior. Thanks!

"Andrew Sarangan" wrote in message
1...
Following the previous discussion on lapse rate, can anyone point me to
source where I can find out how saturated adiabatic lapse rate varies with
temperature? I know that this number increases from 1C/1000' to 3C/1000'
as
the temperature gets colder, but I would like to see a plot or an equation
that describes this behavior. Thanks!


I don't know if I can find you a formula...

But you can look at this diagram:

http://satellite.usask.ca/mcidas/fram32.gif

(It may age, so try to get there quickly. You may want to save the diagram
for reference.... it doesn't change...

I usually use:

http://twister.sbs.ohio-state.edu/skewt.html

but for some reason, only the "pick-a-station" map is available, but all
picks return error 404 no such page. It may come back to life later.
If it does, it will have similar diagrams, only with current real data....)

In the usask diagram, look at the curved purple lines. That is the rate of
cooling for saturated air (saturated adiabatic lapse rate).

Note the temperature lines are light gray, hard to read, leaning to the
right. The light gray, slightly curved, leaning "backwards" to the left,
are the "dry" adiabatic lapse rates (rate of cooling when lifting
unsaturated air).

The green lines are the rate of decrease of dewpoints with lift. (The
numbers on the green lines are "specific" humidity... grams of water vapour
per kg of dry air, related to a specific dewpoint and air pressure)

In all cases, if you are at a starting point between lines, you just follow
upward, parallel to the lines of interest.

If you look at the purple line near plus 28 C at the surface, and lift that
air Saturated to 5800 metres (19,000 ft), it will cool to about 2 degrees,
averaging about 1.35 deg per 1000.

If you start at about minus-5 deg at the surface, and follow parallel to the
purple lines to 5800 meters, you get a drop to about -50, or average of
about 2.37 per 1000 feet. .

These are average cooling over a rather large lift depth. Shorter lifts in
the warmest temperatures (bottom right) cool considerably slower, and in the
coldest temperatures (top left) they are pretty much parallel to the dry
adiabatic rate of cooling.... 3 deg C per 1000.

Note that the saturated rate of cooling does not kick in until the humidity
reaches 100 percent.... in other words, the dewpoint and dewpoint with be
equal....

"Icebound" wrote in message
...
Note that the saturated rate of cooling does not kick in until the
humidity reaches 100 percent.... in other words, the dewpoint and dewpoint
with be equal....



Bah....sorry: "...in other words, the temperature and dewpoint will be
equal..."

"Icebound" wrote in message
...

"Andrew Sarangan" wrote in message
1...
Following the previous discussion on lapse rate, can anyone point me to
source where I can find out how saturated adiabatic lapse rate varies
with
temperature? I know that this number increases from 1C/1000' to 3C/1000'
as
the temperature gets colder, but I would like to see a plot or an
equation
that describes this behavior. Thanks!


I don't know if I can find you a formula...

But you can look at this diagram:



I found this example of the same tephigram diagram, which may be easier to
read that the usask version. Also, the heights are shown in pressure levels
at regular intervals, and it may be easier to interpolate intermediate
heights ( and easier to convert to feet using standard atmosphere
pressure-height conversion).

http://www.eos.ubc.ca/courses/atsc20.../tephigram.pdf

(http://www.usatoday.com/weather/wstdatmo.htm for standard atmosphere
tables)

In this particular version:

Temperature lines are marked T=10, T=20, etc.

Dry adiabatic rate-of-cooling lines are the ones marked with the Greek
letter phi. (phi=0, phi=10, etc. phi represents "potential temperature",
and phi=10, for example. means that air whose temperature-pressure is
anywhere along that line, would reach 10 degrees IF it were lowered to 1000
milibar (hectoPascal) pressure)

The saturated adiabatic rate of cooling lines are the long-dashes, curved.
In this particular version, they stop them at the -40 temperature line,
probably with the idea that beyond that, the rate-of-cooling can be
considered to be pretty much the same as the dry-adiabatic rates.

And the lines along which the dewpoints decrease are dotted... and again,
are labelled with the specific humidity values.

"Icebound" wrote in message
...

In this particular version:

Temperature lines are marked T=10, T=20, etc.

Dry adiabatic rate-of-cooling lines are the ones marked with the Greek
letter phi. (phi=0, phi=10, etc. .............

Okay, so I forgot my Greek for a minute....

All "phi" in the post was supposed to be "THETA", of course.

http://www-frd.fsl.noaa.gov/mab/soundings/java/



"Andrew Sarangan" wrote in message
1...
Following the previous discussion on lapse rate, can anyone point me to
source where I can find out how saturated adiabatic lapse rate varies with
temperature? I know that this number increases from 1C/1000' to 3C/1000'
as
the temperature gets colder, but I would like to see a plot or an equation
that describes this behavior. Thanks!