Re: Calculating tropopause height with function trop_wmo

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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Received on Mon Feb 10 08:12:31 2014