[ncl-talk] Divide by zero error using "pot_vort_isobaric" function

[Dennis Shea]

Kyle is correct.

Basically the 6.3.0 shea_util.ncl had ''back-door' interfaces  to older
versions pot_vort_isobaric and pot_vort_hybrid. These were used for old
testing. Unfortunately, they were not deleted. As 'they' ...my bad!

Please download:
    http://www.cgd.ucar.edu/~shea/contributed.ncl_640


Place these in some directory, load these files in your script. If these
files are in the same directory as your script ...

load "./contributed.ncl_640"
... your_script...

===


The shea_util.ncl_640 need not be loaded. If you decide to do so,
http://www.cgd.ucar.edu/~shea/shea_util.ncl_640

load "./contributed.ncl_640"
load "./shea_util.ncl_640"
... your_script ...

===
If your script still fails, you can upload your script and data files to:

ftp ftp.cgd.ucar.edu
anonymous
your_email
cd incoming
put ...
put ...
...
quit

Then, after successful transfer. let me know.

Cheers
D








On Wed, Mar 9, 2016 at 10:26 PM, Kyle Griffin <ksgriffin2 at wisc.edu> wrote:

> Hi Daniel,
>
> OK, I finally read your email in all the detail I should have the first
> time and found what should likely be an easy fix (this is the 3rd time I've
> written this email - probably shouldn't reply to the list at this hour!).
>
> You're reading a version in from shea_util.ncl, which is an older, out of
> date, and unsupported version of pot_vort_isobaric (anything in
> shea_util.ncl is unsupported, technically - and note the file and line
> numbers in your error message). The safe guards for static stability that
> you've likely seen Dennis and I discuss in previous posts have been fully
> implemented in the contributed.ncl version that became officially supported
> in the 6.3.0 release. I suggest you either comment out your load of
> shea_util.ncl (if possible) or ensure that you load contributed.ncl after
> you load shea_util.ncl - this should ensure the older function is redefined
> when you load contributed.ncl.
>
> Hope that is an easy fix and that your calculations will work now.
>
>
> Kyle
>
> On Wed, Mar 9, 2016 at 6:57 PM Daniel Swain <danielswain2 at gmail.com>
> wrote:
>
>> Hello,
>>
>> I'm currently attempting to use the built-in NCL function to calculate
>> potential vorticity ("pot_vort_isobaric"). Unfortunately, I am repeatedly
>> getting a divide by zero error:
>>
>> "
>> fatal:divide: Division by 0, Can't continue
>> fatal:Div: operator failed, can't continue
>> fatal:["Execute.c":8575]:Execute: Error occurred at or near line 3892 in
>> file $NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl
>> fatal:["Execute.c":8575]:Execute: Error occurred at or near line 3909 in
>> file $NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl
>> "
>>
>> I have confirmed that my original units are in hPa (thus the *100 hPa->
>> Pa conversion should be correct), and that the original latitudes were
>> north->south (so the lat flip should also be correct). I'm assuming this
>> occurring during the static stability calculation (as mentioned in previous
>> ncl-talk discussions), but I'm not sure whether there has yet been a
>> resolution.
>>
>> I've attempted this with data from different years, but eventually a zero
>> division error always crops up. A short sample script is below, and
>> representative data files have been uploaded to the FTP site with the same
>> names as below.
>>
>> I'm currently using NCL version 6.3.0.
>>
>> Thanks very much for any advice!
>>
>> ~Daniel
>>
>> "
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl"
>>
>> begin
>>
>> infile1 = addfile ("air.2013.nc", "r")
>> infile2 = addfile ("uwnd.2013.nc", "r")
>> infile3 = addfile ("vwnd.2013.nc", "r")
>>
>>      U   = infile2->uwnd   ; (time,lev,lat,lon)
>>      V   = infile3->vwnd
>>      T   = infile1->air    ; K
>>
>>      lev = T&level  ; hPa
>>      lev = lev*100 ; convert units
>>      lev at units = "Pa"
>>
>>      U   = U(:,:,::-1,:)    ; reorder to South -> North
>>      V   = V(:,:,::-1,:)
>>      T   = T(:,:,::-1,:)
>>
>>      lat = T&lat
>>      gridType  = 0          ; Gaussian grid
>>      opt = 0
>>      pvort = pot_vort_isobaric(lev,U,V,T,lat, gridType, opt)
>>
>> outfile1=addfile("pvort.2013.nc","c")
>> outfile1->pvort = pvort
>>
>> end
>>
>> "
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