Manually Calculating And Plotting Heights Of Pressure Levels From A Skew T Diagram

[knocker]

My senility is approaching faster than I thought and I'm being totally thick here but how do you manually calculate the height of various pressure levels and thus plot the graph on the chart from a Skew-t diagram? I've done it thousands of times using a Tephigram ( another thermodynamic diagram) but looking at a skew-t I can't see how it's done. I'm obviously missing something obvious. I think a home for destitute met men beckons.

[Coast]

I think these US publications may help WS, but I still struggle with the finer points of Skew T despite John Holmes's excellent work here on NW!

http://www.cs.ubc.ca/~tmm/courses/old533/projects/sancho/proposal/documents/Skew-T-Manual.pdf

http://www.atmos.washington.edu/~houze/301/Miscellaneous/Skew-T.pdf

Worked examples here:

http://www.theweatherprediction.com/thermo/skew-T_tutor/

[knocker]

Thanks Coast I've had a very quick look and I'm not that concerned with the analysis, but the basic principle of calculating the isobaric heights manually. Perhaps I need to look more closely. I feel a little stupid because it can't be that complicated. I agree John's done some sterling work in this area.

[johnholmes]

come on Fred you are the upper air man, I'm just the forecaster!

30 ft=1mb is about all I remember and I've probably got that the wrong way round, or the incorrect value!

3C per 1000ft in old money is another one I vaguely recall.

8mb=6dm?

[Coast]

I'm just the forecaster!

John, hardly just a forecaster!

[knocker]

come on Fred you are the upper air man, I'm just the forecaster!

30 ft=1mb is about all I remember and I've probably got that the wrong way round, or the incorrect value!

3C per 1000ft in old money is another one I vaguely recall.

8mb=6dm?

I know how it is done using a Tephigram John. Perhaps a brief explanation.

Start off, obviously, with the sounding.

Take the average temp fom the surface to 1000mb, or the surface temp if less than a thousand and calculate the 1000mb ht from a scale at the bottom. Obviously it will be negative if the SP is less than a 1000mb. Say the result is 20m for 1000mb.

You then take the average temp from 1000mb-900mb using a clear piece of plastic with a straight line engraved on it. Halfway between the two layers is a horizontal height scale so you read off where your average temp line dissects that. Say 852m. You then add this to the 1000mb height to obtain the 900mb height giving 872m. This procedure is repeated for the 900mb-850mb layer, 850-800 and so on to the top of the sounding. This as you know is because height is a function of temperature.

Thus you end up with a height for each isobaric layer. You can then plot this on the diagram because there is a horizontal height scale that runs from the right to left of the diagram which leaves you with a pressure height curve from which you can read off the height for ant pressure level. And of course this was how contour charts were drawn up just after the Ark and before the days of Sats. and computers. I'm beginning to feel very old. Then I am.

So far so good but when asked this question regarding a Skew t diagram I can't see how it's done because there doesn't appear to be any height scales. It must be possible or how did they manage before computers unless they have changed the blasted diagram.

[johnholmes]

http://weather.uwyo....2012&STNM=72712

has mb and m down left hand side?

or you can call up the raw data for any of the ascents available?

Edited July 20, 2011 by johnholmes

[knocker]

http://weather.uwyo....2012&STNM=72712

has mb and m down left hand side?

or you can call up the raw data for any of the ascents available?

That's true John but can you calculate it manually from the sounding if that height data wasn't supplied?

[johnholmes]

That's true John but can you calculate it manually from the sounding if that height data wasn't supplied?

not the remotest idea Fred but then I simply looked at the wonderful diagrams you lot provided me with-once I had done my first forecast course, with a sigh of relief after the t-phi section, I looked upon t-phi production as some kind of black art!

sorry mate

[knocker]

not the remotest idea Fred but then I simply looked at the wonderful diagrams you lot provided me with-once I had done my first forecast course, with a sigh of relief after the t-phi section, I looked upon t-phi production as some kind of black art!

sorry mate

It was certainly a black art perched on top of 60ft wave trying not to spill your guinness. Put the violins away Fred!

[knocker]

I don't suppose it's of any particular interest but the METO did a factsheet on the breakdown of coded upper messages. It does contain a deliberate error!

http://www.metoffice...factsheet13.pdf

Edited July 20, 2011 by weather ship