Re: Why there are missing values in NARR data?

Xianglei,

 Thanks for your comments. It seems that valid_range = -32766s, 22765s,
which corresponds to 0 ~1 if scale_factor and add_offset are considered.
Why missing values are 32766, but FillValue = -32767 ? see below. What
does this mean?

 Thanks,
 Tao

   snowc:unpacked_valid_range = 0.f, 1.f ;
> > snowc:precision = 4s ;
> > snowc:actual_range = 0.f, 1.f ;
> > snowc:add_offset = 3.2766f ;
> > snowc:scale_factor = 0.0001f ;
> > snowc:missing_value = 32766s ;
> > snowc:valid_range = -32766s, 22765s ;
> > snowc:_FillValue = -32767s ;

----- Original Message -----
From: Xianglei Huang <xianglei_at_umich.edu>
Date: Sunday, May 10, 2009 11:13 am
Subject: Re: Why there are missing values in NARR data?

> Hi Alligator,
>
> Not aware you are NCL user, hoho.
>
> There could be missing data in model output, which means model
> unable
> to give a value there. For example, there should be missing value
> of
> temperature at 1000mb over Tibet Plateau because the surface
> altitude is
> already very high. Your snow cover case, I suspect, is due to
> incompatible and conflicting results of data assimilation, so in
> posteriori fixing, they rather put missing value. Or that place
> with
> snow and rain same time, cannot tell a real snow cover, et al.
>
> Xianglei
>
> Tao.Zhang_at_noaa.gov wrote:
> > Hi,
> >
> > I am trying to regrid NARR (North American Regional Reanlysis)
> data> (netcdf format, see point 2 below) into 2X2 regular netcdf
> grid. I find
> > that the regrided 2X2 netcdf data have values of 6.5532 for snow
> cover,> it is obviously wrong. I print out the original NARR snow
> cover (netcdf
> > format) data (the code is listed in point 1 below), and the message
> > below shows that NARR raw data have values of 6.5532 already. As
> NARR> data is model ouput, there is no reason that the data should
> have> missing values. Actually, the snow cover should range from 0
> to 1.
> > (snowc:unpacked_valid_range = 0.f, 1.f ;
> > snowc:precision = 4s ;
> > snowc:actual_range = 0.f, 1.f ;)
> >
> >
> > Therefore, I am sure that 6.5532 comes from the error calculation
> using> the missing values (6.5532=32766*0.0001+3.2766).
> >
> > But I don't understand why this occurs (there should be no missing
> > values for NARR data as it is model output)? How to get around this
> > missing values?
> >
> > Your suggestions are much appreciated.
> >
> > Thanks,
> > Tao
> >
> >
> >
> >
> > ----------------------------
> > Variable: x
> > Type: float
> > Total Size: 134568816 bytes
> > 33642204 values
> > Number of Dimensions: 3
> > Dimensions and sizes: [348] x [277] x [349]
> > Coordinates:
> > Number Of Attributes: 1
> > _FillValue : -32767
> > (0) min=0 max=6.5532
> >
> >
> > Variable: x (subsection)
> > Type: float
> > Total Size: 386692 bytes
> > 96673 values
> > Number of Dimensions: 2
> > Dimensions and sizes: [277] x [349]
> > Coordinates:
> > Number Of Attributes: 1
> > _FillValue : -32767
> > (0,0) 0
> > (0,1) 0
> > (0,2) 0
> >
> > ......
> > (45,343) 0
> > (45,344) 0
> > (45,345) 0
> > (45,346) 6.5532
> > (45,347) 6.5532
> > (45,348) 6.5532
> > (46,0) 0
> > (46,1) 0
> > (46,2) 0
> > (46,3) 0
> > (46,4) 0
> > (46,5) 0
> > (46,6) 0
> > --------------------------
> >
> >
> >
> >
> >
> >
> > (1) NCL Code
> > ;**************************************************************
> > load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
> > load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
> > load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
> >
> > begin
> > ;*******************************************
> > ; open file and read in data
> > ;*******************************************
> > diri = "../raw_nc/" ; input
> directory> f = addfile (diri+"snowc.mon.mean.nc", "r")
> > ; convert short=>float
> > ; x = short2flt( f->snowc(:,:,:) ) ; (time,lat,lon)
> > ;
> >
> > scale_factor = f->snowc_at_scale_factor
> > add_offset = f->snowc_at_add_offset
> > x = scale_factor * (f->snowc) + add_offset
> >
> > time = f->time
> > lat2d = f->lat ; coordinates
> > lon2d = f->lon
> > dimlc = dimsizes(lat2d) ; dimension sizes
> > nlat = dimlc(0)
> > mlon = dimlc(1)
> > ntime = dimsizes(time)
> > ;
> > print("lat2d: min="+min(lat2d)+" max="+max(lat2d))
> >
> > printVarSummary(x)
> > print(" min="+min(x)+" max="+max(x))
> >
> > print(x(0,:,:))
> > end
> >
> >
> >
> > (2) information about NARR (North American Regional Reanlysis) data
> >
> > netcdf snowc.mon.mean {
> > dimensions:
> > time = UNLIMITED ; // (348 currently)
> > y = 277 ;
> > x = 349 ;
> > nbnds = 2 ;
> > variables:
> > float lat(y, x) ;
> > lat:long_name = "latitude coordinate" ;
> > lat:units = "degrees_north" ;
> > lat:axis = "Y" ;
> > lat:coordinate_defines = "point" ;
> > lat:standard_name = "latitude" ;
> > float lon(y, x) ;
> > lon:units = "degrees_east" ;
> > lon:long_name = "longitude coordinate" ;
> > lon:axis = "X" ;
> > lon:coordinate_defines = "point" ;
> > lon:standard_name = "longitude" ;
> > float x(x) ;
> > x:long_name = "eastward distance from southwest
> corner> of domain in projection coordinates" ;
> > x:units = "m" ;
> > x:standard_name = "projection_x_coordinate" ;
> > float y(y) ;
> > y:long_name = "northward distance from southwest
> corner> of domain in projection coordinates" ;
> > y:units = "m" ;
> > y:standard_name = "projection_y_coordinate" ;
> > int Lambert_Conformal ;
> > Lambert_Conformal:grid_mapping_name =
> > "lambert_conformal_conic" ;
> > Lambert_Conformal:standard_parallel = 50., 50. ;
> > Lambert_Conformal:longitude_of_central_meridian =
> -107. ;
> > Lambert_Conformal:latitude_of_projection_origin =
> 50. ;
> > Lambert_Conformal:false_easting = 5632642.22547 ;
> > Lambert_Conformal:false_northing = 4612545.65137 ;
> >
> > short snowc(time, y, x) ;
> > snowc:units = "1" ;
> > snowc:long_name = "Monthly Snow Cover at Surface" ;
> > snowc:unpacked_valid_range = 0.f, 1.f ;
> > snowc:precision = 4s ;
> > snowc:actual_range = 0.f, 1.f ;
> > snowc:add_offset = 3.2766f ;
> > snowc:scale_factor = 0.0001f ;
> > snowc:missing_value = 32766s ;
> > snowc:valid_range = -32766s, 22765s ;
> > snowc:_FillValue = -32767s ;
> > snowc:GRIB_name = "SNOWC" ;
> > snowc:GRIB_id = 238 ;
> > snowc:var_desc = "snow cover" ;
> > snowc:standard_name = "" ;
> > snowc:level_desc = "Surface" ;
> > snowc:dataset = "NARR Monthly Averages" ;
> > snowc:statistic = "Mean" ;
> > snowc:parent_stat = "Individual Obs" ;
> > snowc:grid_mapping = "Lambert_Conformal" ;
> > snowc:coordinates = "lat lon" ;
> > snowc:cell_methods = "time: mean (monthly from daily
> > values)" ;
> >
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Received on Sun May 10 2009 - 14:49:26 MDT