How high is that cloud?

I picked up a cheap infarred themometer a few days ago and discovered
that it will happily tell me the temperature of the clouds if they
are low.

It seems to me that the temp gradiant from the ground is well known
and if its consistant, this device combined with a table could tell
me how low the coulds are.

For example right now there are clear skys and its reading -27*C.
METAR at hte local airport is claiming 230900Z 19011KT CAVOK 14/09
Q1027 so there should be a 41*C difference between ground and
whatever the thing is reading the temp of in a clear sky. Today
it was reading -8 with a cloud base of at least 5000 ft.

Any comments on this?

-tim
http://web.abnormal.com

Tim Hogard opined

I picked up a cheap infarred themometer a few days ago and discovered
that it will happily tell me the temperature of the clouds if they
are low.

It seems to me that the temp gradiant from the ground is well known
and if its consistant, this device combined with a table could tell
me how low the coulds are.

For example right now there are clear skys and its reading -27*C.
METAR at hte local airport is claiming 230900Z 19011KT CAVOK 14/09
Q1027 so there should be a 41*C difference between ground and
whatever the thing is reading the temp of in a clear sky. Today
it was reading -8 with a cloud base of at least 5000 ft.

Any comments on this?

Clear sky should read 3*A, or about -270*C, the temperature of the cosmic
background radiation .

Cloud base temps should be surfaceTemp - altinThousands * 2. But I could be
wrong.


-ash
Cthulhu in 2005!
Why wait for nature?

"Ash Wyllie" wrote in message
...

Cloud base temps should be surfaceTemp - altinThousands * 2. But I could
be
wrong.


It will be wrong when the lapse rate is different from standard, itself a
significant indicator that something is afoot. When I read a METAR I often
compare the observed ceiling to the surface temp to see if it's close to the
2C/1000 rule or not. If they're lower than they "should be" then you can bet
there's a good chance of convection, turbulence, and generally fast-changing
conditions. At least in New England this really only holds during the warmer
months though.

-cwk.

C Kingsbury opined

"Ash Wyllie" wrote in message
...

Cloud base temps should be surfaceTemp - altinThousands * 2. But I could
be
wrong.


It will be wrong when the lapse rate is different from standard, itself a
significant indicator that something is afoot. When I read a METAR I often
compare the observed ceiling to the surface temp to see if it's close to the
2C/1000 rule or not. If they're lower than they "should be" then you can bet
there's a good chance of convection, turbulence, and generally fast-changing
conditions. At least in New England this really only holds during the warmer
months though.

Good point.



-ash
Cthulhu in 2005!
Why wait for nature?

"C Kingsbury" wrote in message
ink.net...

"Ash Wyllie" wrote in message
...

Cloud base temps should be surfaceTemp - altinThousands * 2. But I could
be
wrong.


It will be wrong when the lapse rate is different from standard, itself a
significant indicator that something is afoot. When I read a METAR I often
compare the observed ceiling to the surface temp to see if it's close to the
2C/1000 rule or not. If they're lower than they "should be" then you can bet
there's a good chance of convection, turbulence, and generally fast-changing
conditions. At least in New England this really only holds during the warmer
months though.

-cwk.

Would you elaborate on this please? Are you talking about comparing the temp/dewpoint spread to the ceiling at
2C/1000?

Cheers,
John Clonts
Temple, Texas
N7NZ

snip
It will be wrong when the lapse rate is different from standard, itself a
significant indicator that something is afoot. When I read a METAR I often
compare the observed ceiling to the surface temp to see if it's close to the
2C/1000 rule or not. If they're lower than they "should be" then you can bet
there's a good chance of convection, turbulence, and generally fast-changing
conditions. At least in New England this really only holds during the warmer
months though.

-cwk.


Would you elaborate on this please? Are you talking about comparing the temp/dewpoint spread to the ceiling at
2C/1000?

I think he's suggesting a comparison between the observed ceiling and the number
of feet you get by dividing the temp/dewpoint difference by 2 and multiplying by
1000. (AGL in both cases.)

If the actual and predicted ceilings are different then the lapse rate is not 2
-- not standard. If the bases are lower, then the lapse rate is deduced to be
larger than 2. And vice versa.

Probably the greatest use of your device is for figuring out the lapse
rate rather than cloud height. Get the cloud height and surface
temperature from METAR, use your device to get the cloud temperature and
calculate the lapse rate. A lapse rate higher than 2C/1000' will
indicate an unstable atmosphere and bumpy flight conditions. Unlike the
temperatures from the winds aloft forecast, yours will be actual
temperature, not forecasted, and will be more accurate. Also, winds
aloft data forecast is not accurate for calculating stability near the
surface, as the temperature is omitted for the first 3000'.
Extrapolating between surface and 6000' may not accurately reflect the
instability close to the ground.




(Tim Hogard) wrote in news:cnv2tr$2n3d$1
@knotty.abnormal.com:

I picked up a cheap infarred themometer a few days ago and discovered
that it will happily tell me the temperature of the clouds if they
are low.

It seems to me that the temp gradiant from the ground is well known
and if its consistant, this device combined with a table could tell
me how low the coulds are.

For example right now there are clear skys and its reading -27*C.
METAR at hte local airport is claiming 230900Z 19011KT CAVOK 14/09
Q1027 so there should be a 41*C difference between ground and
whatever the thing is reading the temp of in a clear sky. Today
it was reading -8 with a cloud base of at least 5000 ft.

Any comments on this?

-tim
http://web.abnormal.com

"Andrew Sarangan" wrote in message
1...
Probably the greatest use of your device is for figuring out the lapse
rate rather than cloud height. Get the cloud height and surface
temperature from METAR, use your device to get the cloud temperature and
calculate the lapse rate. A lapse rate higher than 2C/1000' will
indicate an unstable atmosphere and bumpy flight conditions. Unlike the
temperatures from the winds aloft forecast, yours will be actual
temperature, not forecasted, and will be more accurate. Also, winds
aloft data forecast is not accurate for calculating stability near the
surface, as the temperature is omitted for the first 3000'.
Extrapolating between surface and 6000' may not accurately reflect the
instability close to the ground.

2C per thousand has nothing to do with stability. In unsaturated air,
2C/1000 is stable. In saturated air 2C/1000 is unstable. 2C/1000 is the
standard for calibrating altimeters, it has nothing to do with the real
atmosphere or stability.

Mike
MU-2

On Wed, 24 Nov 2004 15:33:59 GMT, "Mike Rapoport"
wrote:

2C per thousand has nothing to do with stability. In unsaturated air,
2C/1000 is stable. In saturated air 2C/1000 is unstable. 2C/1000 is the
standard for calibrating altimeters, it has nothing to do with the real
atmosphere or stability.

Mike
MU-2




Exactly.

Stability is a function of the actual lapse rate and the dry (or
moist) adiabatic lapse rate.

The dry adiabatic lapse rate is 1C per 100 meters or 5 1/2deg F per
1000 feet.

If the actual lapse rate is more than this, the air is unstable.

In other words, a parcel of air will rise as long as the air around it
is cooler than the parcel. The parcel will be 5 1/2 degrees F cooler
after rising 1000 ft. If the surrounding air at 1000 feet is still
cooler than the cooled parcel, the parcel keeps on rising. It will
keep on rising (and cooling) until the parcel is the same
temperature as the surrounding air, which has its own (different)
lapse rate.

That's why its smoother above cumulus clouds. The clouds mark the top
of the column of rising air.

"Mike Rapoport" wrote in message link.net...
2C per thousand has nothing to do with stability. In unsaturated air,
2C/1000 is stable. In saturated air 2C/1000 is unstable. 2C/1000 is the
standard for calibrating altimeters, it has nothing to do with the real
atmosphere or stability.

Mike
MU-2

Adiabatic lapse rate is 1C/1"Hg for moist air (depending on moisture
content) and 3C/1"Hg for dry air. 2C/1"Hg is a representative average
for somewhat moist but unsaturated air. It is still a useful indicator
of stability. I would not discount is as a completely meaningless
number. It is a useful reference, just like 29.92" and 15C.

Please explain how 2C/1000 is used in altimeter calibration. I did not
know altimeters had any temperature corrections.