[ncl-talk] Maybe I found a bug of the function "dpres_plevel"

[Deniz Bozkurt]

Dear NCL,

I would like to learn if there has been any progress on this reported bug when one uses certain pressure levels (e.g., 700hPa to 300hPa).

Regards,

Deniz

--
Deniz Bozkurt, PhD
Post-doctoral Fellow
Center for Climate and Resilience Research
Department of Geophysics, University of Chile
Blanco Encalada 2002, Santiago, Chile
E-mail: dbozkurt at dgf.uchile.cl <mailto:dbozkurt at dgf.uchile.cl>, deniboz at gmail.com <mailto:deniboz at gmail.com>Web: http://dgf.uchile.cl/~dbozkurt/ <http://dgf.uchile.cl/%7Edbozkurt/>



> On Oct 19, 2015, at 8:11 PM, Dennis Shea <shea at ucar.edu> wrote:
> 
> Thank you for sending the file. There is a bug.
> 
> If you use ptop=0 or ptop=min(levels)=200, there is no bug. The [
> psfc-ptop ] differences match the sum of the layer thickness.
> 
> However, if you use a ptop > min(levels) [for example, ptop=500] a
> small subset [0.7%] of the grid points  do not sum correctly.
> 
> I am out tomorrow. I will look on Wednesday.
> 
> Regards
> Dennis Shea
> 
> 
> 
> 
> On Tue, Oct 13, 2015 at 11:56 PM, Bilbo Qiu <biloisbrave at gmail.com> wrote:
>> Dear everyone,
>> 
>> It's my first time to send the email. I am trying to describe the problem
>> briefly as possible.
>> 
>> Version:  NCL 6.3.0
>> 
>> System: Ubuntu
>> 
>> No errors.
>> 
>> Warning: dpres_plevel: At one or more grid points the sum of the layer
>> thicknesses is not equal to (psfc-ptop). Are units of plev, psfc and ptop
>> matching?
>> 
>> Problems: I tried to calculate the pressure layer thickness "dp", using the
>> function "dpres_plevel". The input file is "ps_qv.nc", which includes two
>> variables, ps (surface pressure) and qv(specific humidity). I exported the
>> result to a file named "dp.nc". A warning displayed as the above. I checked
>> all of the units. It is "Pa". I visualized "dp.nc", using ncview and found
>> dp is about 3000 Pa on Tibet Plateau on the level of 1000 hPa where the
>> surface pressure is about 550 hPa. There should be no value on Tibet Plateau
>> where the surface pressure is much below 1000 hPa. In addition, there exists
>> extreme value about 30000 pa on the top level of 700 hPa on the boundary of
>> Tibet Plateau. The value is too big for dp. Below is my script:
>> --------------------------------
>> begin
>>   diri = "./"
>>   fili = "ps_qv.nc"
>>   fi   = addfile(diri+fili, "r")
>> 
>>   q  = fi->qv(0,0:12,:,:) ; (levels, latitude, longitude), it will provide
>> coordinate information for dp
>> 
>>   psfc  = fi->ps(0,:,:)   ; (lat,lon), the unit of the variable "ps" in the
>> input file is Pa
>>   psfc at units = "Pa"
>>   printVarSummary(psfc)
>>   printMinMax(psfc, 0)
>> 
>>   ;isobaric levels
>>    plev = fi->levels(0:12) ;from 1000 to 700 hPa
>>  plev = plev*100. ;the unit of plev is hPa, convert it to Pa by *100
>>    plev at units = "Pa"
>>    printVarSummary(plev)
>>    printMinMax(plev, 0)
>> 
>>    ptop= 70000
>>  ptop at units = "Pa"
>> 
>>    dp  = dpres_plevel(plev, psfc, ptop, 0) ; the key function
>>  copy_VarCoords(q, dp)
>>    printVarSummary(dp)
>>    printMinMax(dp, 0)
>> ;output dp to a netCDF file
>> system("/bin/rm -f dp.nc")   ; remove any pre-existing file
>> ncdf = addfile("dp.nc" ,"c")  ; open output netCDF file
>> fAtt               = True            ; assign file attributes
>> fAtt at title         = "NCL Simple Approach to netCDF Creation"
>> fAtt at source_file   =  "original-file.nc"
>> fAtt at Conventions   = "None"
>> fAtt at creation_date = systemfunc ("date")
>> fileattdef( ncdf, fAtt )            ; copy file attributes
>> filedimdef(ncdf,"time",-1,True)
>> ncdf->dp  = dp
>> end
>> -----------------------------------
>> 
>> I couldn't find the source code of the function "dpres_pleve" and had no
>> idea where the errors are.
>> 
>> I am looking forwards to your help.
>> 
>> Additions: I set the surface pressure to a constant, 101800 Pa. The result
>> makes sense. I am wondering if the function is wrong when the surface
>> pressure is a 2-D or 3-D array.
>> 
>> Bilbo Qiu
>> 
>> 
>> 
>> 
>> 
>> 
>> 
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