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[IDV #EGO-120295]: Longitude range 0 to -1.85 in NCEP model grids



Greetings Brian,

I grabbed the file PRES.sfc.1878.ens.grb from 
ftp://ftp.cdc.noaa.gov/Public/gcompo/Brian.Mapes/ and checked it
out.

It looks like the the longitude variable goes from 0.0 to -363.68866 by
a step of -1.9041291, which means your grid wraps around itself. It's
possible that it was encoded wrong in the GRIB file (it also could be a
bug, so I'll pass it along to the netCDF-Java group, just in case). It would
seem to me that with 192 longitude values, the step should be more
like 1.875. I've attached an ncml file that forces the longitudes to use the
1.875 step value, and it seems to work correctly. Can you check it out and
let me know if it looks correct to you? If you haven't used ncml before,
simply place the attached file in the same directory as your grib file and
load the ncml through the IDV instead of the grib file directly (note that
if you open the ncml file in a text editor, you will see that the original grib
file is referenced in the first line).

Cheers,

Sean

PS. We generally do not have a problem loading NCEP model output.
That said, we sometimes do have to 'fix' their grib files due to errors
they made when encoding the grib files.

> Hello IDV folks.
> 
> I have trouble accessing this NCEP model generated gridded data set,
> because the grib file has minLon 0 and maxLon -1.875
> (which should be interpreted as 360-1.875 but isn't).
> 
> The dataset is 500 MB and is available on an ftp area for now
> (see forwarded email below with details).
> 
> It might be worth a couple lines of core code?
> NCEP models are a pretty common data source.
> 
> I'd ideally like to access this for my class this Tuesday (while Sandy is 
> hot).
> The October Gale of 1878 rather resembled Sandy, it seems.
> 
> Thank you for the great training (and support),
> Brian Mapes
> 
> 
> Brian,
> 
> Bummer. It means that IDV isn't following the standard.
> That is a valid grid description (and not ours - it is native the NCEP model).
> 
> gil
> 
> 
> On 10/31/12 9:26 AM, Brian Mapes wrote:
> The grib longitudes go from 0 to -1.875 so IDV chokes on it. :(
> 
> :GRIB_param_La1 = 88.542; // double
> :GRIB_param_La2 = -88.542; // double
> :GRIB_param_Lo1 = 0.0; // double
> :GRIB_param_Lo2 = -1.875; // double
> 
> From: Gil Compo address@hidden<mailto:address@hidden>]
> Sent: Tuesday, October 30, 2012 5:40 PM
> To: Brian Mapes
> Subject: Re: assimilation lesson for undergrads?
> 
> Brian,
> 
> The retrieval from the NERSC tape Science Gateway can be pretty slow.
> So, I grabbed surface pressure for the year 1878 (year of the October Gale of 
> 1878
> http://www.hpc.ncep.noaa.gov/research/roth/galeof78.htm)
> 
> and put it in
> 
> ftp://ftp.cdc.noaa.gov/Public/gcompo/Brian.Mapes/
> 
> -rwxr-xr-x   1 gcompo  PSD\climate  4812230080 Oct 30 15:37 
> PRES.sfc.1878.ens.grb*
> 
> This has all 56 members and the first guesses for every 3 hours.
> Analyses are only made every 6 hours, but use the values from 3 hours to 9 
> hours out.
> We haven't kept those 9 hour values.
> 
> The corresponding analysis file is at
> http://portal.nersc.gov/pydap/20C_Reanalysis_ensemble/analysis/ps/
> 
> I'd get that for you, too, but our system is going down soon for monthly 
> maintenance.
> 
> 
> Hope that this helps,
> 
> best wishes,
> 
> gil
> 
> 
> 
> 
> 
> 
> On 10/30/12 12:17 PM, Brian Mapes wrote:
> IDV can read all sorts of grib formats etc.
> Maybe I'll play with this at the IDV training.
> 
> Thanks for the leads!
> Brian
> 
> On Oct 30, 2012, at 12:18 PM, Gil Compo wrote:
> 
> Brian,
> 
> Nothing really off hand. No ppts or anything like that.
> 
> 
> You could compare the spread field (ensemble standard deviation) of the 20CR 
> first guess pressure valid at the same time as
> the 20CR analysis pressure
> 
> Individual members of the analysis in netCDF4 (and opendap accessible) are at
> http://portal.nersc.gov/pydap/20C_Reanalysis_ensemble/analysis/
> (variable is "ps")
> 
> 
> 
> but the first guess pressure would take more than a week to put together in 
> netCDF4.
> They are in GRIB at  
> http://portal.nersc.gov/archive/home/projects/incite11/www/20C_Reanalysis/everymember_grib_indi_fg_variables/PRES
> 
> 
> Hope this helps.
> 
> best wishes,
> gil
> 
> On 10/30/12 9:03 AM, Brian Mapes wrote:
> Hi Gil.
> 
> Know any good material on assimilation for undergrads, for my
> synoptic lab class? I use IDV bundles to drive everything home
> visually.
> 
> It's getting untenably hard these days to show a 6h forecast with enough error
> that the analysis visibly draws to some raw datums, says my
> predecessor teacher of the class.
> 
> I thought to show an ensemble and see the spread collapse, but
> maybe that is just as hard with the 6h window and models as
> good as they are.
> 
> Any brainstorm ideas welcome. Or datasets if you have a run with a
> longer window, or from a less data rich time when ensembles are more
> dramatically affected by obs... I could build a nice illustrative IDV bundle 
> if you
> had a good set of netCDF files of how assimilation works in 20C. Or heck
> maybe you have ppts of this for explaining the whole system to general
> science level audiences.
> 
> I'm actually in Boulder this week for IDV training.
> But won't see you unless by chance.
> ANyway I have til next week to prepare this lesson.
> 
> Thanks,
> Brian
> 
> Brian Mapes
> address@hidden<mailto:address@hidden>
> 
> 
> 
> 
> 
> 
> --
> +++++++++++++++++++++++++++++++++++++++++++++++++++
> Gil Compo, Research Scientist, CIRES
> University of Colorado
> 
> Mail : CIRES Climate Diagnostics Center
> NOAA Physical Sciences Division
> Earth System Research Laboratory
> 325 Broadway R/PSD1, Boulder, CO 80305-3328
> Email: address@hidden<mailto:address@hidden>
> Phone: (303) 497-6115 Fax: (303) 497-6449
> http://www.esrl.noaa.gov/psd/people/gilbert.p.compo
> +++++++++++++++++++++++++++++++++++++++++++++++++++
> "Stop and consider the wondrous works of God."
> Job 37:14
> ---------------------------------------------------
> The contents of this message are mine personally
> and do not necessarily reflect any position of
> NOAA or the University of Colorado.
> 
> 
> Brian Mapes
> address@hidden<mailto:address@hidden>
> 
> 
> 
> 
> 
> 
> --
> +++++++++++++++++++++++++++++++++++++++++++++++++++
> Gil Compo, Research Scientist, CIRES
> University of Colorado
> 
> Mail : CIRES Climate Diagnostics Center
> NOAA Physical Sciences Division
> Earth System Research Laboratory
> 325 Broadway R/PSD1, Boulder, CO 80305-3328
> Email: address@hidden<mailto:address@hidden>
> Phone: (303) 497-6115 Fax: (303) 497-6449
> http://www.esrl.noaa.gov/psd/people/gilbert.p.compo
> +++++++++++++++++++++++++++++++++++++++++++++++++++
> "Stop and consider the wondrous works of God."
> Job 37:14
> ---------------------------------------------------
> The contents of this message are mine personally
> and do not necessarily reflect any position of
> NOAA or the University of Colorado.
> 
> 
> 
> 
> --
> +++++++++++++++++++++++++++++++++++++++++++++++++++
> Gil Compo, Research Scientist, CIRES
> University of Colorado
> 
> Mail : CIRES Climate Diagnostics Center
> NOAA Physical Sciences Division
> Earth System Research Laboratory
> 325 Broadway R/PSD1, Boulder, CO 80305-3328
> Email: address@hidden<mailto:address@hidden>
> Phone: (303) 497-6115 Fax: (303) 497-6449
> http://www.esrl.noaa.gov/psd/people/gilbert.p.compo
> +++++++++++++++++++++++++++++++++++++++++++++++++++
> "Stop and consider the wondrous works of God."
> Job 37:14
> ---------------------------------------------------
> The contents of this message are mine personally
> and do not necessarily reflect any position of
> NOAA or the University of Colorado.
> 
> 
> Brian Mapes
> address@hidden<mailto:address@hidden>
> 
> 
> 
> 
> 

Ticket Details
===================
Ticket ID: EGO-120295
Department: Support IDV
Priority: Normal
Status: Open

Attachment: PRES.sfc.1878.ens.ncml
Description: Binary data


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