"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....