Re: Calculating tropopause height with function trop_wmo

From: Dennis Shea <shea_at_nyahnyahspammersnyahnyah>
Date: Mon Feb 10 2014 - 09:13:38 MST

You can change the 'critical lapse rate' via the 'opt' argument.
See the argument description and the 'Description' section.

Perhaps, this would solve your issue.

On 2/10/14, 8:12 AM, Kyle Griffin wrote:
> Hi Patrick,
>
> Just going by the WMO statement on the function's documentation page, it
> looks to be working OK.
>
> https://www.ncl.ucar.edu/Document/Functions/Built-in/trop_wmo.shtml
>
> "The first tropopause is defined as the lowest level at which
>
>
> the lapse rate decreases to 2 deg K per kilometer or less,
> provided also the average lapse rate between this level and
> all higher levels within 2 kilometers does not exceed 2 deg K."
>
> Linked below is an image I quickly made from altering your script
> which shows that above your tropopause height (in red), there is a 1km
> layer with a lapse rate of over double the allowable limit (nearly
> 5K/km). Since no such layer is allowed within 2km above the trop_wmo
> level's definition, it keeps going to a higher level that does not
> contain such relatively unstable levels above it. While I do think
> that the trop_wmo layer could be around 15km instead of 16km, that
> might be something to look for in the function's code that Dennis sent
> you. It's possible it just looks at layers using a nice even
> thousand-meter increment and the unstable layer might barely go above
> 15km in this case.
>
> Link to height profile version:
> http://marrella.meteor.wisc.edu/~ksgriffin2/share/tlogp.png
>
> Hope this helps some...
>
>
>
> Kyle
>
>
> ----------------------------------------
> Kyle S. Griffin
> Department of Atmospheric and Oceanic Sciences
> University of Wisconsin - Madison
> Room 1421
> 1225 W Dayton St, Madison, WI 53706
> Email: ksgriffin2@wisc.edu
>
>
> On Mon, Feb 10, 2014 at 8:47 AM, Duran, Patrick T <pduran@albany.edu> wrote:
>
>> Greetings NCL users,
>>
>>
>> I have been using the trop_wmo function to calculate tropopause heights,
>> and have noticed that for a few of the soundings (5% at most), the height
>> calculated by the function does not seem reasonable. One example may be
>> found here:
>> http://www.atmos.albany.edu/student/pduran/ncl_talk/060709_1200.png
>>
>>
>> On the left is a standard SkewT and on the right is a plot of T
>> vs. logP. The orange horizontal line indicates the tropopause level
>> calculated by trop_wmo, and the red line indicates the tropopause
>> calculated by a script that I wrote using the same WMO
>> definition included in the trop_wmo documentation. I do not understand
>> why trop_wmo places the tropopause within the approximately isothermal
>> layer just below 100 mb...
>>
>>
>> Though the trop_wmo calculation and my calculation agree very closely
>> for the vast majority of cases, the few cases where they do not agree lead
>> me to question how the trop_wmo function performs the tropopause
>> calculation. Does anybody know how precisely trop_wmo calculates the
>> tropopause? Your help is greatly appreciated.
>>
>>
>> If you're interested, here is the sounding data file and script that I
>> used:
>>
>> Sounding data:
>> http://www.atmos.albany.edu/student/pduran/ncl_talk/03937-0607091200-RAWIN_6S-BOGFIX-T8C_KM-100m-loc.edit_QC_QC2
>>
>>
>> NCL script:
>> http://www.atmos.albany.edu/student/pduran/ncl_talk/tropopause_height.ncl.
>>
>>
>> Thanks very much,
>>
>> Patrick Duran
>>
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>
>
>
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Received on Mon Feb 10 09:13:46 2014

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