"Mr Blowman" S@not here.karoo.co.uk wrote in message
...
To calculate thickness values in DAM I have always used the eqution
(1000mB - SLP ) * 0.87 )+ 500 mB height. Is this correct as I cannot
explain the 0.87 constant factor.

Decrease in pressure with height is 1hPa per 0.87 dam, roughly.

"Mr Blowman" S@not here.karoo.co.uk wrote in message
...

"Steve" wrote in message
...

"Mr Blowman" S@not here.karoo.co.uk wrote in message
...
To calculate thickness values in DAM I have always used the eqution
(1000mB - SLP ) * 0.87 )+ 500 mB height. Is this correct as I cannot
explain the 0.87 constant factor.

Decrease in pressure with height is 1hPa per 0.87 dam, roughly.




Thanks Steve


Do you have an official source available as a link, thanks in advance .

Regards

Sean B



Apologies for my incorrect date setting.


Regards

Sean B

"Mr Blowman" S@not here.karoo.co.uk wrote in message
...

"Mr Blowman" S@not here.karoo.co.uk wrote in message
...

"Steve" wrote in message
...

"Mr Blowman" S@not here.karoo.co.uk wrote in message
...
To calculate thickness values in DAM I have always used the eqution
(1000mB - SLP ) * 0.87 )+ 500 mB height. Is this correct as I cannot
explain the 0.87 constant factor.

Decrease in pressure with height is 1hPa per 0.87 dam, roughly.


Do you have an official source available as a link, thanks in advance .



No it was OTTOMH, but you could try searching for "degridding" in the FAQ

There's a whole thread taking place further upstream about Gianna being 1
HOUR FAST!!. Blimey you're a full 24hrs fast. Well that's what's showing on
the post time.
Is that due to not being able to wait for christmas for a snowflake or two?.

"Mr Blowman" S@not here.karoo.co.uk wrote in message
...
To calculate thickness values in DAM I have always used the eqution
(1000mB - SLP ) * 0.87 )+ 500 mB height. Is this correct as I cannot
explain the 0.87 constant factor.


Regards


Sean B

"lawrence Jenkins" wrote in message
...
There's a whole thread taking place further upstream about Gianna being 1
HOUR FAST!!. Blimey you're a full 24hrs fast. Well that's what's showing
on
the post time.
Is that due to not being able to wait for christmas for a snowflake or
two?.

"Mr Blowman" S@not here.karoo.co.uk wrote in message
...
To calculate thickness values in DAM I have always used the eqution
(1000mB - SLP ) * 0.87 )+ 500 mB height. Is this correct as I cannot
explain the 0.87 constant factor.


Regards


Sean B





See my previous appology in the thread Lawrence, just reinstalled XP and set
the date wrong, I'm sorry it has caused you any undue inconvenience!


Regards

Sean B


Oh and PS Merry Christmas

No of course it didn't cause any inconvenience. I don't get me knickers in a
twist over such things. I was just amused after poor Gianna sends a
christmas card to us all, I poked fun at it and others were vexed by the
hour time difference thus creating a long thread. I bet she wished she
hadn't bothered. Then to top it all you were a day fast. It really doesn't
matter but it made me smile. Mind you it's bloody hard to find greenwich GMT
on the xp install list.





"Mr Blowman" S@not here.karoo.co.uk wrote in message
...

"lawrence Jenkins" wrote in message
...
There's a whole thread taking place further upstream about Gianna being
1
HOUR FAST!!. Blimey you're a full 24hrs fast. Well that's what's showing
on
the post time.
Is that due to not being able to wait for christmas for a snowflake or
two?.

"Mr Blowman" S@not here.karoo.co.uk wrote in message
...
To calculate thickness values in DAM I have always used the eqution
(1000mB - SLP ) * 0.87 )+ 500 mB height. Is this correct as I cannot
explain the 0.87 constant factor.


Regards


Sean B





See my previous appology in the thread Lawrence, just reinstalled XP and
set
the date wrong, I'm sorry it has caused you any undue inconvenience!


Regards

Sean B


Oh and PS Merry Christmas

I am not sure if you are asking for the exact formula, but in case you are,
it is:

Z' = R*T/g*ln(p1/p2)

Where Z' is the thickness of the layer in metres bounded by pressure
surfaces p1 and p2.
R is the universal gas constant (287) for dry air, T is the mean temperature
of the layer (in deg K),
and g is the gravitational acceleration standard (9.80665).

Also, for pressure levels where p1/p2 is close to unity, the approximate
form is probably close enough:

Z' = R*T/g*p'/p

where p' is the pressure difference between top and bottom of the layer, and
p is the mean pressure.

For a mean temperature of zero C, your factor would be 0.80 for Z' in DAM,
and for 20C it would be 0.86. (pressure difference of 1 mbar at 1000 mbar).







--
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.btinternet.com/~wokingham.weather/wwp.html
"Mr Blowman" S@not here.karoo.co.uk wrote in message
...
To calculate thickness values in DAM I have always used the eqution
(1000mB - SLP ) * 0.87 )+ 500 mB height. Is this correct as I cannot
explain the 0.87 constant factor.


Regards


Sean B

lawrence Jenkins wrote:

christmas card to us all, I poked fun at it and others were vexed by the
hour time difference thus creating a long thread.

Vexed? Must be a problem with my server, I didn't see those. Just some
helpful people trying to get things right. I'd have thought that in a
..sci newsgroup containing weather reports and forecasts, the ordering
and correct timestamping of posts would be important; perhaps I'm wrong.

--
Steve Loft, Wanlockhead, Dumfriesshire. 1417ft ASL
http://www.wanlockhead.org.uk/weather/
Free weather softwa http://cumulus.nybbles.co.uk/
Experimental webcam: http://www.wanlockhead.org.uk/webcam.php

I will only say this. It seemed to me like writing out a nice card for
somebody and then being grammatically corrected. It could have waited....
or did I miss a very important issue here?


"Steve Loft" wrote in message
...
lawrence Jenkins wrote:

christmas card to us all, I poked fun at it and others were vexed by the
hour time difference thus creating a long thread.

Vexed? Must be a problem with my server, I didn't see those. Just some
helpful people trying to get things right. I'd have thought that in a .sci
newsgroup containing weather reports and forecasts, the ordering and
correct timestamping of posts would be important; perhaps I'm wrong.

--
Steve Loft, Wanlockhead, Dumfriesshire. 1417ft ASL
http://www.wanlockhead.org.uk/weather/
Free weather softwa http://cumulus.nybbles.co.uk/
Experimental webcam: http://www.wanlockhead.org.uk/webcam.php

Lawrence Jenkins wrote:
I will only say this. It seemed to me like writing out a nice card for
somebody and then being grammatically corrected. It could have waited....
or did I miss a very important issue here?

shrug Gianna seemed to appreciate it.

Now, Lawrence, about this top-posting...
--
Steve Loft, Wanlockhead, Dumfriesshire. 1417ft ASL
http://www.wanlockhead.org.uk/weather/
Free weather softwa http://cumulus.nybbles.co.uk/
Experimental webcam: http://www.wanlockhead.org.uk/webcam.php