All,
The following is a response to a question posed
>Date: Thu, 23 Mar 2006 13:15:26 +0100
>Hi all,
>[snip] but I couldn't find
>anything to solve my problems, anyway,
>I got an ECMWF operational analysis via the MARS
>archive, (only Z,U,V,Q-rel.hum.-,T for 4 press levels),
>In my ncl script I print out the variables and
>the isobaric levels:
[snip]
The ECMWF operational analysis referred to is on a *very*
high resolution grid: NLAT=800, MLON=1600.
The file name is "ana_yest.grb". The contents of the
file may be viewed at:
http://www.cgd.ucar.edu/web/public_html/shea/ncl_filedump.ana.yest
One variable, Q_GDS4_ISBL (specific humidity) is on
the 800x1600 grid.
float Q_GDS4_ISBL ( lv_ISBL0, g4_lat_4, g4_lon_5 )
4 800 1600
long_name : Specific humidity
units : kg kg**-1
Thus, Q_GDS4_ISBL can readily be read and plotted via NCL. EG: See:
http://www.cgd.ucar.edu/web/public_html/shea/Q.1000.800x1600.gif
---- All other variables are in "complex coefficient" form. A sample complex coefficient variable [temperature] looks like float T_GDS50_ISBL( lv_ISBL0, real_imaginary, g50_lat_2, g50_lon_3 ) 4 2 800 800 long_name : Temperature units : K The data fields must be reconstructed [synthesized] prior to plotting. In all previous occurrences, NCL's spherical harmonic synthesis functions and procedues have always been able to reconstruct the variables. In fact, they exactly agree with ECMWF's AMOS software. However, when the standard approach was used on these 800x800 coefficients, the generated fields contained numerical exceptions [NaNs]. The 'problem' is that the standard recursive methods used for the Legendre polynomials are not converging. Currently, it looks like nlat up to 646 will converge, ===== nlat = 646 Dimensions and sizes: [lat | 646] x [lon | 1292] Temperature: min=232.126 max=303.634 ===== nlat= 648 Dimensions and sizes: [lat | 648] x [lon | 1296] Temperature: min=nan0x7fffffff max=nan0x7fffffff ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ===== Thus, currently the full 800x1600 grids can not be generated from the full set of complex coefficients. In practice, the very high numbered coeffients are near zero so the additional information is not significant. A script that reads/synthesizes/plots all variables on the file is at http://www.cgd.ucar.edu/web/public_html/shea/ecmwf.800x1600.ncl Q is plotted at 800x1600. The variables generated from spherical harmonics are synthesized to a 640x1280 grid. An example for temperature is at: http://www.cgd.ucar.edu/web/public_html/shea/T.1000.800x1600.gif If anyone has questions regarding the script, please feel free to contact me directly. Dennis Shea _______________________________________________ ncl-talk mailing list ncl-talk_at_ucar.edu http://mailman.ucar.edu/mailman/listinfo/ncl-talkReceived on Wed May 10 2006 - 11:38:12 MDT
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