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 Post subject: Lapse Rates
PostPosted: Tue May 05, 2009 3:00 am 
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Joined: Tue May 05, 2009 2:55 am
Posts: 3
Hello all,

I am fairly new to Digital Atmosphere. I am working on a project that deals
with 700-500 mb lapse rates. Is there any way that digital atmosphere can
contour lapse rates based on archived RAOB data? For example, I would like
to be able to calculate, plot, and subsequently contour 700-500mb lapse rates
based on observed RAOB data for 28 Aug 1973. I have the dataset, but not sure
if the software has this capability. Before posting this query, I used the
search feature here and could not find any subject on the matter.

Best Regards,

Mike


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 Post subject: Lapse rates
PostPosted: Tue May 05, 2009 6:16 pm 
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Joined: Sun Nov 13, 2005 10:03 pm
Posts: 97
Location: Mid-Wales
Firstly, I am not a meteorologist but from the definition as being the rate of change of temperature going vertically through the atmosphere, I guess you want to chart the temperature difference between 700mb and 500mb.

This script will produce contour lines using upper air data downloaded from within DA.

#700-500mb lapse rate script
ANALYZE,CONT CINT=1 DASH COLOR=200:0:0 SDIF=1:2 STOR=2 TEMP H500 STOR=1 TEMP H700

Regards


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 Post subject:
PostPosted: Wed May 06, 2009 2:50 am 
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Thanks very much. Would it be possible to divide the result by 2.5? This would give the the result in terms of degrees C per Kilometer (C/km).


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 Post subject:
PostPosted: Wed May 06, 2009 7:33 pm 
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Joined: Sun Nov 13, 2005 10:03 pm
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Location: Mid-Wales
Dividing the result by 2.5 will not give you the lapse rate in deg C per Km.
It would only give you the ratio of the temperature differences between 700mb and 500mb.

For a lapse rate to be calculated per Km the 700mb and 500mb heights (HGHT 700 and HGHT 500) must be taken to produce a thickness figure at any one point.
Height difference between 700mb and 500mb should be divided by 1000 to produce Km.

The 700mb and 500mb temperature difference should be divided by the height difference figure (Km) to produce a lapse rate in deg C/Km.

Mathematically:
(TEMP700 - TEMP500) / ((HGHT500 - HGHT700) / 1000)

Does that make sense?

Regards


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 Post subject:
PostPosted: Wed May 06, 2009 10:18 pm 
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Joined: Tue May 05, 2009 2:55 am
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Thanks for the explanation. I guess I was trying to keep things a bit simpler (and approximate). The script you sent me calculates T700-T500. The 700mb layer is generally found around 3 km AGL and the 500mb level about 5.5km AGL (a difference of 2.5 km). Therefore (T700-T500)/2.5 results in a close approximation of 700-500mb lapse rate in units of C/km.

However, I like your way better. Could you write a script that calculates that?


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 Post subject:
PostPosted: Thu May 07, 2009 3:40 am 
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The script below works approximately (assumes your 700-500mb height difference is 2.6 km):

ANALYZE,CONT CINT=0.5 dash COLOR=200:0:0 STOR=4 SDVC=3:2.6 STOR=3 SDIF=1:2 STOR=2 TEMP H500 STOR=1 TEMP H700

I can't quite get it to work as I would like. We'd ideally take lapse rate as the temperature difference divided by the *actual* height difference. The following script yields a invalid floating point error. Perhaps someone can see what I've done incorrectly...

ANALYZE,CONT CINT=0.5 DASH COLOR=200:0:0 STOR=8 SMLC=7:-1000 STOR=7 SDVD=3:6 STOR=6 SDIF=4:5 STOR=5 HGHT H500 STOR=4 HGHT H700 STOR=3 SDIF=1:2 STOR=2 TEMP H500 STOR=1 TEMP H700

Any thoughts?


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 Post subject: SDVD syntax not working
PostPosted: Thu May 07, 2009 1:45 pm 
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Location: Mid-Wales
I was writing the script and everything was fine until I reached the division stage where the syntax uses SDVD and I see someone else hit the same problem.

It appears the SDVD function doesn't work and only gives an invalid floating point error.
I have simplified the script to almost nothing and tested each part but once SDVD is inserted, an error occurs.

Maybe Tim doesn't know about this as searching this forum regarding scripting, I cannot find any reference or example script that uses SDVD.

SDVD should be the syntax to divide the Temp difference by the Hght difference.

Therefore until someone can explain how to divide 2 numbers using a script in DA, you will have to use your approximation script for now.

Regards


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 Post subject:
PostPosted: Thu May 07, 2009 4:37 pm 
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Joined: Thu May 07, 2009 3:35 am
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Thanks for the info on the SDVD function - I appreciate you testing things out! Hopefully a solution can be found...the software is otherwise quite impressive.


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