[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: netCDF and WRF grids

This archive contains answers to questions sent to Unidata support through mid-2025. Note that the archive is no longer being updated. We provide the archive for reference; many of the answers presented here remain technically correct, even if somewhat outdated. For the most up-to-date information on the use of NSF Unidata software and data services, please consult the Software Documentation first.

  • Subject: Re: netCDF and WRF grids
  • Date: Tue, 04 Sep 2007 17:23:16 -0600
Hi Robert:

I have no doubt that you are finding real bugs; the WRF projections are quite 
difficult to understand; in earlier versions the parameters are actually 
wrong(!). If you can email sample files and whatever fixes you think are right, 
i will test and see if i can corroborate. I will be gone till next week, so i 
will look at it then.

The NMM E grid is a completely different beast than the ARP grid. I need to 
detect and probably just branch to some new code. I spent a while figuring it 
out but didnt finish, i think because since it was rotated, it violated some 
assumptions in the GeoGrid code. I think theres some 2D arrays we could use 
instead that might be a workaround, but i forget the details. I can look at 
that again next week also.

John

Robert B. Schmunk wrote:


John,

A couple questions/problems regarding using the NJ libraries to
read some sample WRF datasets which have been provided me by
a group at NOAA.

First, I have enabled my Panoply application to recognize WRF
(polar) stereographic data and use the NJ libraries to project it
onto a standard grid. This seems to work just great for northern
hemisphere data, but it turns out that southern hemisphere data
(e.g., Tasmania) is distorted. I have looked at the code for the
Stereographic class, and that seems okay, but I am wondering if
the calculation of "scaleFactor" in line 185 of the WRFConvention
is correct. I note that it doesn't seem to adjust for the change
of sign when lat1 is less than 0 (i.e., in the S.H.), and so
for example, if lat1 = -90deg, scaleFactor would be 0.

If you need it, I can e-mail you the sample S.H. stereographic
dataset. It's about 2 MB.

The second issue regards another WRF grid which apparently is
not yet handled by the NJ libraries, the WRF NMM "E" grid, also
identified as MAP_PROJ=203. The comments in the the WRFConvention
class seem to suggest that dealing with this grid is a hairball,
i.e., I see the scary phrase "special processing". Does this
mean that the likelihood of the NJ libraries being able to
re-project this grid in the foreseeable future is dim?

Also regarding the NMM "E" grid, the sample NOAA dataset I have
is causing WRFConvention to puke a NullPointerException at line
144. Checking the file metadata, I find it contains neither the
GLAT variable which s supposed to be created at line 143 of
WRFConvention, nor the GLON variable to be created further down
at line 149. Is this something that WRFConvention needs to trap
for?

rbs

--
Robert B. Schmunk, address@hidden
NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025