[ncl-talk] (I)PV units?

Dennis Shea shea at ucar.edu
Thu Sep 8 09:12:51 MDT 2016


Hi Kacie,

I see the  issue.

As noted in the documentation:

http://www.ncl.ucar.edu/Document/Functions/Contributed/pot_vort_isobaric.shtml

   "Compute potential vorticity on isobaric levels and a global rectilinear
grid."
----
After you regrid, you have a rectilinear grid. However, it is not "global."
EG:

Variable: tkReGr

Number of Dimensions: 3

Dimensions and sizes:   [lv_ISBL3 | 29] x [lat | 337] x [lon | 831]

Coordinates:

            lv_ISBL3: [100..1000]

            lat: [   1..  85]                         <====   Regional grid
            lon: [ 150..358.5]                   <====

The 'pot_vort_isobaric' function uses spherical harmonic functions to
calculate the required meridional and zonal gradients. The spherical
harmonic functions are "highly accurate" however they require global grids.

===
As I recall, in the summer NCL Workshop, we discussed this issue. :-)

As an exercise, I suggested that you copy and modify 'pot_vort_isobaric' to
use the 6.4.0 'grad_latlon_cfd' function to replace the spherical harmonic
gradient functions.


http://www.ncl.ucar.edu/Document/Functions/Contributed/grad_latlon_cfd.shtml

Some gradient examples are at:
http://www.ncl.ucar.edu/Applications/gradients.shtml

Actually, in your script, you have a commented line:
   ;load "/grid-scratch/kshourd/code/potVortCFD.ncl"

So .... it looks like you have a created a function but you did not use
it???

===
I decided to create a function 'pot_vort_isobaric_cfd'. It has slightly
different arguments.
See attached.

Likely, I will include 'pot_vort_isobaric_cfd' in the 6.4.0 release as part
of contributed.ncl

D


On Wed, Sep 7, 2016 at 12:31 PM, Kacie Shourd <Kacie.Shourd at dri.edu> wrote:

> Hi all,
>
>
>
> I am encountering some problems with my potential vorticity (PV) and
> subsequent isentropic potential vorticity calculations (IPV). The patterns
> I am getting look right, but the magnitude of the values does not make
> sense. I assume pot_vort_isobaric() function outputs in raw units rather
> than PVUs?
>
>
>
> I have checked my units/script over and over and over again, and cannot
> figure out why the values are a few orders of magnitude off. It seems as
> though maybe my pressure values are being input into the equations wrong
> (or some other variable is). The patterns of PV make sense for the event,
> but the magnitude is most certainly wrong.
>
>
>
> Any insight into what I am doing wrong or any other reasons the calculated
> PV values are coming out  really large. Scripts, output, and necessary
> files to run script can be found here: ftp://pubfiles.dri.edu/pub/
> kshourd/nclTalkIPVHelp/ , and variable summaries are as follows:
>
>
>
> ---
>
> Variable: tkReGr
>
> Type: float
>
> Total Size: 32485452 bytes
>
>             8121363 values
>
> Number of Dimensions: 3
>
> Dimensions and sizes:   [lv_ISBL3 | 29] x [lat | 337] x [lon | 831]
>
> Coordinates:
>
>             lv_ISBL3: [100..1000]
>
>             lat: [   1..  85]
>
>             lon: [ 150..358.5]
>
> Number Of Attributes: 15
>
>   sub_center :  The North American Regional Reanalysis (NARR) Project
>
>   center :      US National Weather Service - NCEP (WMC)
>
>   long_name :   Temperature
>
>   units :       K
>
>   _FillValue :  1e+20
>
>   level_indicator :     100
>
>   grid_number : 221
>
>   parameter_table_version :     131
>
>   parameter_number :    11
>
>   model :       North American Regional Reanalysis (NARR)
>
>   forecast_time :       0
>
>   forecast_time_units : hours
>
>   initial_time :        09/26/2010 (18:00)
>
>   remap :       remapped via ESMF_regrid_with_weights: Bilinear
>
>   missing_value :       1e+20
>
>
>
> ---
>
> Variable: uN
>
> Type: float
>
> Total Size: 32485452 bytes
>
>             8121363 values
>
> Number of Dimensions: 3
>
> Dimensions and sizes:   [lv_ISBL3 | 29] x [lat | 337] x [lon | 831]
>
> Coordinates:
>
>             lv_ISBL3: [100..1000]
>
>             lat: [   1..  85]
>
>             lon: [ 150..358.5]
>
> Number Of Attributes: 15
>
>   sub_center :  The North American Regional Reanalysis (NARR) Project
>
>   center :      US National Weather Service - NCEP (WMC)
>
>   long_name :   u-component of wind
>
>   units :       m/s
>
>   _FillValue :  1e+20
>
>   level_indicator :     100
>
>   grid_number : 221
>
>   parameter_table_version :     131
>
>   parameter_number :    33
>
>   model :       North American Regional Reanalysis (NARR)
>
>   forecast_time :       0
>
>   forecast_time_units : hours
>
>   initial_time :        09/26/2010 (18:00)
>
>   remap :       remapped via ESMF_regrid_with_weights: Bilinear
>
>   missing_value :       1e+20
>
>
>
> ---
>
> Variable: vN
>
> Type: float
>
> Total Size: 32485452 bytes
>
>             8121363 values
>
> Number of Dimensions: 3
>
> Dimensions and sizes:   [lv_ISBL3 | 29] x [lat | 337] x [lon | 831]
>
> Coordinates:
>
>             lv_ISBL3: [100..1000]
>
>             lat: [   1..  85]
>
>             lon: [ 150..358.5]
>
> Number Of Attributes: 15
>
>   sub_center :  The North American Regional Reanalysis (NARR) Project
>
>   center :      US National Weather Service - NCEP (WMC)
>
>   long_name :   v-component of wind
>
>   units :       m/s
>
>   _FillValue :  1e+20
>
>   level_indicator :     100
>
>   grid_number : 221
>
>   parameter_table_version :     131
>
>   parameter_number :    34
>
>   model :       North American Regional Reanalysis (NARR)
>
>   forecast_time :       0
>
>   forecast_time_units : hours
>
>   initial_time :        09/26/2010 (18:00)
>
>   remap :       remapped via ESMF_regrid_with_weights: Bilinear
>
>   missing_value :       1e+20
>
>
>
> ---
>
> Variable: p
>
> Type: integer
>
> Total Size: 116 bytes
>
>             29 values
>
> Number of Dimensions: 1
>
> Dimensions and sizes:   [lv_ISBL3 | 29]
>
> Coordinates:
>
>             lv_ISBL3: [100..1000]
>
> Number Of Attributes: 2
>
>   long_name :   isobaric level
>
>   units :       Pa
>
>
>
> ---
>
> Variable: thetaN
>
> Type: float
>
> Total Size: 32485452 bytes
>
>             8121363 values
>
> Number of Dimensions: 3
>
> Dimensions and sizes:   [lv_ISBL3 | 29] x [lat | 337] x [lon | 831]
>
> Coordinates:
>
>             lv_ISBL3: [100..1000]
>
>             lat: [   1..  85]
>
>             lon: [ 150..358.5]
>
> Number Of Attributes: 5
>
>   _FillValue :  1e+20
>
>   long_name :   potential temperature
>
>   units :       K
>
>   remap :       remapped via ESMF_regrid_with_weights: Bilinear
>
>   missing_value :       1e+20
>
>
>
> --- (FROM tkReGr&lv_ISBL3)
>
> Variable: p
>
> Type: integer
>
> Total Size: 116 bytes
>
>             29 values
>
> Number of Dimensions: 1
>
> Dimensions and sizes:   [lv_ISBL3 | 29]
>
> Coordinates:
>
> Number Of Attributes: 2
>
>   long_name :   isobaric level
>
>   units :       Pa
>
>
>
> ---
>
> Variable: ipv
>
> Type: float
>
> Total Size: 4480752 bytes
>
>             1120188 values
>
> Number of Dimensions: 3
>
> Dimensions and sizes:   [thlev | 4] x [lat | 337] x [lon | 831]
>
> Coordinates:
>
>             thlev: [325..370]
>
>             lat: [   1..  85]
>
>             lon: [ 150..358.5]
>
> Number Of Attributes: 4
>
>   _FillValue :  1e+20
>
>   long_name :   Isentropic Potential Vorticity at 325K
>
>   short_name :  IPV
>
>   units :       K m2/kg/s
>
>
>
>
>
> Thanks!!
>
> Best,
>
> Kacie
>
> ---
>
> Kacie N. Shourd
>
> 드림
>
>
>
> Graduate Research Assistant
>
> Desert Research Institute
>
> Kacie.Shourd at dri.edu
>
> Work: (775) 674-7049
>
>
>
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