Hello , meteorology wizards.

The problem as it stated:
Non-saturated air parcel is adiabatically lifted from 10 C 900 mbar up
to 660 mbar, where fog appears.
I ploted it on the tephigram:
http://img503.imageshack.us/my.php?i...ewpoint7ma.jpg

The question is:
What the dew point temp of the parcel @ 660 mbar, @800 mbar?

For 660 mbar the answer is rather easy - it's around Td= -17 C.
For 800 mbar, i got confused:
a) assuming that water mixing ratio is const, we follow blue line and
get Td =-15 C for 800 mbar
it looks like it's too high for this pressure level, maybe I should
b) follow the red line of wet adiabat to get Td=-5 C , which seems more
reasonable for Tparcel=0 C

Thanks in advance for your answers.

You were right the first time by following the mixing ratio line (blue). The
example shows just how easy it is to saturate a dry airmass by deep
mixing/lift. Granted this much lift (900-660) is quite excessive, even for
the US High Plains.

Furthermore, whoever posed this problem needs to check his/her own work. How
can fog, a ground based phenomenon, occur at 660mb in this scenario?

Honestly have never heard of a "Tephigram" before, in reference to a
SkewT/LogP diagram. Interesting. More interesting how you're using what
looks like official British stationery from the 1950s. Hope that's not an
original :-D

"Billy" wrote in message
oups.com...
Hello , meteorology wizards.

The problem as it stated:
Non-saturated air parcel is adiabatically lifted from 10 C 900 mbar up
to 660 mbar, where fog appears.
I ploted it on the tephigram:
http://img503.imageshack.us/my.php?i...ewpoint7ma.jpg

The question is:
What the dew point temp of the parcel @ 660 mbar, @800 mbar?

For 660 mbar the answer is rather easy - it's around Td= -17 C.
For 800 mbar, i got confused:
a) assuming that water mixing ratio is const, we follow blue line and
get Td =-15 C for 800 mbar
it looks like it's too high for this pressure level, maybe I should
b) follow the red line of wet adiabat to get Td=-5 C , which seems more
reasonable for Tparcel=0 C

Thanks in advance for your answers.

"wxforecaster" wrote in message
...
Honestly have never heard of a "Tephigram" before, in reference to a
SkewT/LogP diagram. Interesting. More interesting how you're using
what looks like official British stationery from the 1950s. Hope
that's not an original :-D

.... if you've got a stack of them, hang on to 'em! They are like gold
dust over here ;-)

Martin. (in the UK)


--
FAQ & Glossary for uk.sci.weather at:-
http://homepage.ntlworld.com/booty.weather/uswfaqfr.htm
and
http://booty.org.uk/booty.weather/metindex.htm

On Fri, 16 Dec 2005 17:46:55 GMT,
wxforecaster , in
wrote:

+ Furthermore, whoever posed this problem needs to check his/her own
+ work. How can fog, a ground based phenomenon, occur at 660mb in this
+ scenario?

Well, let's just abstract to more general terms and say "reaches
saturation". Now, whether that actually condenses into a visible
object is another question.

Of course, you're correct in noting that fog is nothing more than a
cloud in contact with the ground. Fog can indeed occur at 660mb, if
you're in the right location:

http://www.peakware.com/highest.html?list=8000

That's at the "Roof of the World". So possible, if not particularly
likely.

+ Honestly have never heard of a "Tephigram" before

Tephigram: derives its name from its coordinates of temperature and
entropy (T, phi). It was introduced by Sir Napier Shaw ("Manual of
Meteorology," vol. 2, p. 36; vol. 3, pp. 223-224, Cambridge University
Press, London 1926, 1930). [1]

Goodness. They're old, and not particularly well-liked by us moderns,
but where used prior to the introduction of the skew-t. One major
drawback of the tephigram is that it's difficult to estimate the
potential energy (CAPE) from a plot.

Nowadays, that's not really an issue, as we'd just use a computer to
compute all the relevant derived quantities for us. But we still plot
up soundings on the skew-t 'cause that's what we're used to.

If you're more interested, you might want to reference Byers (page 129).

[1] Byers, Horace "General Meteorology" 1959, ISBN 0-07-009500-0.

James
--
Consulting Minister for Consultants, DNRC
I can please only one person per day. Today is not your day. Tomorrow
isn't looking good, either.
I am BOFH. Resistance is futile. Your network will be assimilated.

Awesome! Thanks for the great info on the tephigram.

P.S. Wasn't suggesting that fog can't occur at 660mb (on the right mountain
peak), but in the example given, a parcel was lifted from 900mb and I think
it's beyond a reasonable assumption that 660mb wasn't the ground (or
anywhere close). )))


"I R A Darth Aggie" wrote in message
...
On Fri, 16 Dec 2005 17:46:55 GMT,
wxforecaster , in
wrote:

+ Furthermore, whoever posed this problem needs to check his/her own
+ work. How can fog, a ground based phenomenon, occur at 660mb in this
+ scenario?

Well, let's just abstract to more general terms and say "reaches
saturation". Now, whether that actually condenses into a visible
object is another question.

Of course, you're correct in noting that fog is nothing more than a
cloud in contact with the ground. Fog can indeed occur at 660mb, if
you're in the right location:

http://www.peakware.com/highest.html?list=8000

That's at the "Roof of the World". So possible, if not particularly
likely.

+ Honestly have never heard of a "Tephigram" before

Tephigram: derives its name from its coordinates of temperature and
entropy (T, phi). It was introduced by Sir Napier Shaw ("Manual of
Meteorology," vol. 2, p. 36; vol. 3, pp. 223-224, Cambridge University
Press, London 1926, 1930). [1]

Goodness. They're old, and not particularly well-liked by us moderns,
but where used prior to the introduction of the skew-t. One major
drawback of the tephigram is that it's difficult to estimate the
potential energy (CAPE) from a plot.

Nowadays, that's not really an issue, as we'd just use a computer to
compute all the relevant derived quantities for us. But we still plot
up soundings on the skew-t 'cause that's what we're used to.

If you're more interested, you might want to reference Byers (page 129).

[1] Byers, Horace "General Meteorology" 1959, ISBN 0-07-009500-0.

James
--
Consulting Minister for Consultants, DNRC
I can please only one person per day. Today is not your day. Tomorrow
isn't looking good, either.
I am BOFH. Resistance is futile. Your network will be assimilated.

//You were right the first time by following the mixing ratio line
(blue). The
example shows just how easy it is to saturate a dry airmass by deep
mixing/lift. Granted this much lift (900-660) is quite excessive, even
for
the US High Plains.//

Thanks, wxforecaster

//Furthermore, whoever posed this problem needs to check his/her own
work. How
can fog, a ground based phenomenon, occur at 660mb in this scenario? //

As I R A Darth Aggie noted, the meaning of this fog: "parcel reaches
saturation".


//Honestly have never heard of a "Tephigram" before, in reference to a
SkewT/LogP diagram. Interesting. More interesting how you're using what
looks like official British stationery from the 1950s. Hope that's not
an
original :-D //

To say the truth , I never heard that "fog" is tied in some way to the
ground, but hell I've got an excuse: I'm not english native speaker ;-)

Cheers