Re: converting time variable to actual dates from a regular .nc file from NCEP Reanalysis-2 data

From: Dave Allured - NOAA Affiliate <dave.allured_at_nyahnyahspammersnyahnyah>
Date: Tue Sep 03 2013 - 19:41:00 MDT

Arthur,

All zeros in the input variable "time" suggests a bad input file, and
will give you the invalid output that you are seeing.

So before using NCL, check the file with ncdump -v time. If "hgt.nc"
was made by processing original files downloaded from the PSD
archives, such as concatenating, then please check both the process
and the original files.

If you find a bad original file, try downloading with FTP software,
not a web browser. Browser downloads are known to create problems
with files from the PSD archives.

--Dave A.
NOAA/PSD/CIRES Climate Analysis Branch

On Tue, Sep 3, 2013 at 3:27 PM, A.J. Eiserloh <arthur.eiserloh@gmail.com> wrote:
> Hi,
>
> I downloaded Reanalysis-2 data and I am just trying to make it convert the
> time variable from the .nc file to the real dates (11/26/2012 00Z
> --12/05/2012 00Z). This means there are 37 times. The units for the times
> are "hours since 1800-1-1 00:00:0.0". I am trying to use the function
> calendar_decode2(), but when I print the result, It just gives me back the
> dates with the 1800-01-01 date. It seems like it is not using the
> actual_range attribute for the time variable. Also, why does the time
> variable come with all zeros instead of the actual times from the
> actual_range attribute. I am using NCL v6.1.1. Can someone please help me
> find a solution to my problem?
>
> Here is my code:
>
> ;data source = Reanalysis-2 geopotential height.
> ;
> http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis2.pressure.html
> ;==============================================================
>
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
> load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/calendar_decode2.ncl"
>
> f = addfile("./hgt.nc","r")
>
> ;geopotential height
>
> hgt = short2flt(f->hgt) ; hgt(time,lev,lat,lon)
> ; short2flt() function uses scale_factor
> and add_offset attribute to convert
> time = f->time
> lat = f->lat
> lon = f->lon
> plev = f->level
>
> print(time)
> ;time@units = "hours since 1800-1-1 00:00:00"
> times = calendar_decode2(time,-3)
> print(times)
>
> This is the variable summary for time in my .nc file:
>
> double time(time) ;
> time:units = "hours since 1800-1-1 00:00:0.0" ;
> time:long_name = "Time" ;
> time:actual_range = 1866264., 1866480. ;
> time:delta_t = "0000-00-00 06:00:00" ;
> time:standard_name = "time" ;
> time:axis = "T" ;
> time:coordinate_defines = "point"
>
> This is the output from my code:
>
> Variable: time
> Type: double
> Total Size: 296 bytes
> 37 values
> Number of Dimensions: 1
> Dimensions and sizes: [time | 37]
> Coordinates:
> time: [ 0.. 0]
> Number Of Attributes: 7
> units : hours since 1800-1-1 00:00:0.0
> long_name : Time
> actual_range : ( 1866264, 1866480 )
> delta_t : 0000-00-00 06:00:00
> standard_name : time
> axis : T
> coordinate_defines : point
> (0) 0
> (1) 0
> (2) 0
> (3) 0
> (4) 0
> (5) 0
> (6) 0
> (7) 0
> (8) 0
> (9) 0
> (10) 0
> (11) 0
> (12) 0
> (13) 0
> (14) 0
> (15) 0
> (16) 0
> (17) 0
> (18) 0
> (19) 0
> (20) 0
> (21) 0
> (22) 0
> (23) 0
> (24) 0
> (25) 0
> (26) 0
> (27) 0
> (28) 0
> (29) 0
> (30) 0
> (31) 0
> (32) 0
> (33) 0
> (34) 0
> (35) 0
> (36) 0
>
>
> Variable: times
> Type: integer
> Total Size: 148 bytes
> 37 values
> Number of Dimensions: 1
> Dimensions and sizes: [37]
> Coordinates:
> Number Of Attributes: 1
> calendar : standard
> (0) 1800010100
> (1) 1800010100
> (2) 1800010100
> (3) 1800010100
> (4) 1800010100
> (5) 1800010100
> (6) 1800010100
> (7) 1800010100
> (8) 1800010100
> (9) 1800010100
> (10) 1800010100
> (11) 1800010100
> (12) 1800010100
> (13) 1800010100
> (14) 1800010100
> (15) 1800010100
> (16) 1800010100
> (17) 1800010100
> (18) 1800010100
> (19) 1800010100
> (20) 1800010100
> (21) 1800010100
> (22) 1800010100
> (23) 1800010100
> (24) 1800010100
> (25) 1800010100
> (26) 1800010100
> (27) 1800010100
> (28) 1800010100
> (29) 1800010100
> (30) 1800010100
> (31) 1800010100
> (32) 1800010100
> (33) 1800010100
> (34) 1800010100
> (35) 1800010100
> (36) 1800010100
>
>
>
>
> Thanks,
>
> --
> Arthur J. Eiserloh, Jr.
> San Jose State University
> Graduate Student
> Dept. of Meteorology and Climate Science
>
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Received on Tue Sep 3 19:41:09 2013

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