Can anyone tell me how to calculate dam air values from 500mb heigth charts,
for instance :-


http://www.wetterzentrale.de/pics/Rukm1441.html


Thanks in advance.


Regards


Sean B

"Buzz" wrote in message


Can anyone tell me how to calculate dam air values from 500mb heigth charts,
for instance :-


http://www.wetterzentrale.de/pics/Rukm1441.html


Thanks in advance.


Regards


Sean B



http://groups.google.com/groups?hl=e...news.com#link2
or
http://tinyurl.com/2bz76

I get a strange feeling of deja-vous :-)

Jon.



--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG

Thanks Jon

Yes that was me, I'd just forgot.


Regards


Sean B


"Jon O Rourke" wrote in message
news:ed67b53d1fd3be087cb5dc0be1b98953.62236@mygate .mailgate.org...
"Buzz" wrote in message


Can anyone tell me how to calculate dam air values from 500mb heigth
charts,
for instance :-


http://www.wetterzentrale.de/pics/Rukm1441.html


Thanks in advance.


Regards


Sean B




http://groups.google.com/groups?hl=e...&th=1ba35c8901
fa9fd3&seekm=uun9a5d7jvp39e%40corp.supernews.com#l ink2
or
http://tinyurl.com/2bz76

I get a strange feeling of deja-vous :-)

Jon.



--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG

When we consider the dam air values we are talking about the thickness of
the layer between 1000mb and 500mb. It is measured in decimeters (tens of
metres) such that 10dm (or dam) = 100m or the famous 528dm = 5280m (or just
over 5 kilometres).

The thickness of the layer is then the height of the 500mb surface minus the
height of the 1000mb surface.

If we take the example where the surface pressure is 1000mb then the height
of the 1000mb surface above the ground is zero. The thickness can then be
read straight off as the height of the 500mb surface, such as the area
neatly circling Denmark on the map you have linked. He

(Height of 500mb) - (Height of 1000mb) = (thickness of layer)
(520dm) - (0m) = (520dm)

In other parts of the map where the surface pressure is not as convenient we
have to calculate the height of the 1000mb surface off the ground. We do
this using a rough version of the hydrostatic balance equation:

height of 1000mb surface = (surface pressure - 1000mb)*100 / (11.8)

For example, at the high centre on your map over the Atlantic:

height of 1000mb surface = (1040mb - 1000mb)*100 / 11.8
= 4000 / 11.8 = 339m = 34dm

Carrying on to find thickness...

Thickness = Height of 500mb - Height of 1000mb
570dm - 34dm = 536dm

Hope this helps,

Jeremy

PS Alternatively you could find a map that shows the lines of thickness!
They are around somewhere but I'm afraid I don't know where to find them.



"Buzz" wrote in message
...
Can anyone tell me how to calculate dam air values from 500mb heigth
charts,
for instance :-


http://www.wetterzentrale.de/pics/Rukm1441.html


Thanks in advance.


Regards


Sean B

"Jeremy Handscomb" wrote in message
...

PS Alternatively you could find a map that shows the lines of
thickness!
They are around somewhere but I'm afraid I don't know where to find
them.



http://www.westwind.ch/?page=gfsg

there are others: but don't get 'hung-up' on thickness (500-1000hPa) ..
it's useful, but for tracing low-level airmasses, use ThetaE or similar.

Martin.

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

Jon O Rourke wrote in message ...
:I get a strange feeling of deja-vous :-)

Or even perhaps "déjà vu". Déjà vu = already seen; déjà vous = already
you.

Colin Youngs
Brussels

Jeremy Handscomb wrote:
When we consider the dam air values we are talking about the thickness of
the layer between 1000mb and 500mb. It is measured in decimeters (tens of
metres) such that 10dm (or dam) = 100m or the famous 528dm = 5280m (or just
over 5 kilometres).


Actually *decameters* and the simbol is *dam*

dm is decimeter, that is 1/10 of a meter.

"Martin Rowley" wrote in message
...

"Jeremy Handscomb" wrote in message
...

PS Alternatively you could find a map that shows the lines of
thickness!
They are around somewhere but I'm afraid I don't know where to find
them.



http://www.westwind.ch/?page=gfsg

there are others: but don't get 'hung-up' on thickness (500-1000hPa) ..
it's useful, but for tracing low-level airmasses, use ThetaE or similar.

Martin.

ThetaW data is now available here up to T+72,
http://meteocentre.com/models/modelsukmet_eur_e.html

Jon.

Actually *decameters* and the simbol is *dam*

dm is decimeter, that is 1/10 of a meter.



Or "decametre" and "metre" as we call them on this side of the pond.
It's easy to get the thickness. Take the surface pressure, subtract 1000
and multiply what's left by 0.8. Thus 1020 mb gives you 16, and 980 would give
you -16. Subtract this from the 500 mb height( in decametres). You now have
the thickness to sufficient accuracy. The GFS charts show thickness under the
heading "Mittl. Wolken" (mean cloudiness) but only every 18 dam. As has been
said, thickness lines are useful, but not the be-all and end-all.

Tudor Hughes, Warlingham, Surrey.

My mistake!

Jeremy

"Alex" wrote in message
news
Jeremy Handscomb wrote:
When we consider the dam air values we are talking about the thickness
of
the layer between 1000mb and 500mb. It is measured in decimeters (tens
of
metres) such that 10dm (or dam) = 100m or the famous 528dm = 5280m (or
just
over 5 kilometres).


Actually *decameters* and the simbol is *dam*

dm is decimeter, that is 1/10 of a meter.