Re: netCDF and WRF grids

Hi Robert:

Ive confirmed your correction for the scaleFactor, I will include in next 
release. Thanks very much. Turns out it also affects the AWIPS files, though 
they may not be used in the southern hemisphere.

The NMM E grid set doesnt have the expected variables (GLAT,GLON). It also doesnt have any versioning info, or valid time coordinates. It does have 

:TITLE = "OUTPUT FROM GRIDGEN";

which may mean its an intermediate file, meant for input to the model.

I will get a fix to it, but not right away. let me know if thats a problem.

BTW, I am now assuming Java 1.5. Are you still on 1.4?

John


Robert B. Schmunk wrote:
> John,
>
> I decided to try compiling NJ from source again. For some
> reason, it was less trouble than I remember from the past.
>
> Regarding handling of the polar stereographic in WRF
> datasets, I found that the southern hemisphere problem
> could indeed be easily fixed by correcting line 185 of
> WRFConvention.java. In other words, the line which reads
>
> double scaleFactor = (1+Math.sin(Math.toRadians(lat1)))/2.;
>
> should instead be
>
> double scaleFactor = (1+Math.abs(Math.sin(Math.toRadians(lat1))))/2.;
>
> I haven't tried any changes regarding the NMM E grid yet.
>
> rbs
>
>
>
>
>
>
>
> On Sep 4, 2007, at 19:54, Robert B. Schmunk wrote:
>
> > On Sep 4, 2007, at 19:23, John Caron wrote:
> >
> > > 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.
> >
> > John, I have placed the three sample WRF netCDF files from
> > NOAA in an anonymous ftp directory at
> >
> > ftp://ftp.giss.nasa.gov/outgoing/caron
> >
> > The file names are alaska.nc, tasmania.nc, and geo_nmm.d01.nc.
> > They add up to about 11 MB.
> >
> > The alaska and tasmania files are both polar stereographic
> > files. alaska is the north polar and seems to be read correctly
> > by the combination of NJ's WRFConvention.java and Stereographic.java
> > classes, while tasmanian is the south polar and shows the problem
> > which I described. As indicated, I suspect this is a problem with
> > the scaleFactor variable calculated in WRFConvention.java. However,
> > my own experience with trying to compile the NJ libraries from
> > source was messy enough that in this case I haven't tried to make
> > the change myself.
> >
> > geo_nmm.d01.nc is the NMM E file.
> >
> > > 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.
> >
> > By "rotated" do you mean that the alternative grid is some form of
> > a rotated pole?
> >
> > I haven't seen (well, haven't looked too hard for) NMM E grid
> > documentation, so don't know what it entails. If it is indeed
> > some form of rotated pole grid, it seems like it shouldn't be
> > too difficult to attack since, as you know, I have already
> > written my own rotated pole transformation code. The main thing
> > is just figuring out where the pole is rotated to.
> >
> > rbs
> >
> >
> >
> > > 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
>
> --
> Robert B. Schmunk, address@hidden
> NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025