[ncl-talk] Era-Interim daily precipitation
Dennis Shea
shea at ucar.edu
Mon Jun 4 17:56:14 MDT 2018
I am going to add a few more items to a previous response:
The
*Golden Rules of data processing are:(a) Look at your data!*
*(b) Know your data!*
*(c) Make sure *you* know what a function or tool is doing to your data*
*---*
The source netcDF '2_2_ERAI_Prec_2015_Jan_00_12_12.nc' was created from a
GRIB file:
history attribute:
2018-05-16 09:15:25 GMT by grib_to_netcdf-2.7.3: grib_to_netcdf
/data/data05/scratch/3c/71/_mars-atls00-a562cefde8a29a7288fa0b8b7f9413f7-b4mPzK.grib
-o /data/data04/scratch/41/14/_grib2netcdf-atls17-a562cefde8a29a7288fa0b8b7f9413f7-PZaKeY.nc
-utime" ;
---
There are *62 time steps* on the source ERAI file:
yyyymmddhh tp value
(0) ERAI: 2015010112 0.000330344
*<=== only one value for this calendar day*(1) ERAI: 2015010200
0.0051588 ......* two time steps per calendar day* ...
(2) ERAI: 2015010212 0.00401913
(3) ERAI: 2015010300 0
(4) ERAI: 2015010312 0
(5) ERAI: 2015010400 0
(6) ERAI: 2015010412 0.000478998
(7) ERAI: 2015010500 0.00344653
[SNIP]
(55) ERAI: 2015012900 0
(56) ERAI: 2015012912 0
(57) ERAI: 2015013000 9.35942e-05
(58) ERAI: 2015013012 7.15703e-05
(59) ERAI: 2015013100 0.00390901
(60) ERAI: 2015013112 0
(61) ERAI: 2015020100 0.00183889* <=== only one value for this
calendar day*
---
To what 'time' does the source ERAI 'time stamp apply"?
That is ****USER RESPONSIBILITY*** *to know or find the answer.
Three possibilities:
[1] beginning
[2] end
[3] 'center-of-mass' ... mid temporal time?
---
NCL's '*calculate_daily_values*' with *'ncrit=2*' requires two values on
the *same calendar day*
https://www.ncl.ucar.edu/Document/Functions/
Contributed/calculate_daily_values.shtml
With *ncrit=2* the function returns 30 values ... not 31 or 32. Why?
Because it requires 2 values per calendar date. It ignores the 1st and last
times because there is only one time step per calendar day
tp2_ncl
NCL_tag : calculate_daily_values: arith=sum
----
The function 'tags' it with the *1st time step of each *complete* calendar
day*
(0) NCL: 2015010200 0.00917792
(1) NCL: 2015010300 0
(2) NCL: 2015010400 0.000478998
(3) NCL: 2015010500 0.00879252
[SNIP]
(28) NCL: 2015013000 0.000165164
(29) NCL: 2015013100 0.00390901
---
The CDO takes the first two values [0,1], then the next two [2,3], etc.
It 'tags' the time as the 2nd time step
(0) CDO: 2015010200 0.00548913
(1) CDO: 2015010300 0.00401912
(2) CDO: 2015010400 -1.08611e-10
[SNIP]
(29) CDO: 2015013100 0.00398058
(30) CDO: 2015020100 0.00183889
Even though the time 'tags' are the same, they refer to different sums.
---
NCL can be made to handle the time and data any way the user wants.
I'll let you look at the attached script and output
On Fri, Jun 1, 2018 at 4:03 PM, Ehsan Taghizadeh <ehsantaghizadeh at yahoo.com>
wrote:
> Dears,
> About summation of 12 hours precipitation to obtain daily precipitation,
> as suggested me I used "cdo" and it seems work correctly:
> "cdo -b F32 -f nc4c -z zip timselsum,2 2_2_ERAI_Prec_2015_Jan_00_12_12.nc
> 2_2_ERAI_Prec_2015_Jan_24_cdo.nc4"
> However I like to know how writing nc files with "Geo2D".
>
> Sincerely
> Ehsan
>
> On Thursday, May 31, 2018, 7:12:17 PM GMT+4:30, Ehsan Taghizadeh <
> ehsantaghizadeh at yahoo.com> wrote:
>
>
> Thank you so much for your nice replies.
> With you comment, it seems work correctly. However I've added some changes
> to the script to have an output file same as input file, I mean about
> dimensions, attributes, and so on.
> However I have some difficulties about it and I'll be thankful if I could
> have your help, again.
> For example about
> fout->tp24_1!1 = tp!1
> fout->tp24_1!2 = tp!2
> I encountered error. It seems they have conflict with following lines:
> fout->latitude = fin->latitude
> fout->longitude = fin->longitude
>
> Beside that I want to have "tp24_1" with dimension "Geo2D" to plot.
> I attached new version of script, and I'll be thankful if I hear from you.
>
> Sincerley
> Ehsan
> On Thursday, May 31, 2018, 6:44:48 PM GMT+4:30, Dennis Shea <shea at ucar.edu>
> wrote:
>
>
> The *golden rule* of data processing is *look at your data*
>
> You have:
>
> tp=f->tp ; <=== type 'short' [ packed data]
>
> However, your file has:
>
> *short* tp ( time, latitude, longitude )
> * scale_factor *: 5.505649013956001e-06
> *add_offset *: 0.1803980955369768
> _FillValue : -32767
> missing_value : -32767
> units : m
> long_name : Total precipitation
>
> You **MUST* *unpack the variable before computing the sums.
>
> tp = *short2flt*(f->tp)
>
> printVarSummary(tp)
> printMinMax(tp,0)
>
> ===
> https://www.ncl.ucar.edu/Document/Functions/Contributed/short2flt.shtml
>
>
>
>
>
>
> On Thu, May 31, 2018 at 7:19 AM, Ehsan Taghizadeh <
> ehsantaghizadeh at yahoo.com> wrote:
>
> Dears,
> I've tried sum 12 hour precipitation to obtain 24 hour precipitation using
> attached script.
> However it seems doesn't work correctly!
> I had to sum tp(0,:,:)+tp(1,:,:), also tp(2,:,;)+tp(3,;,:), and so on.
> I uploaded "2_2_ERAI_Prec_2015_Jan_00_12_12.nc" in ftp.cgd.ucar.edu.
> I'll be thankful if I hear from you.
>
> Sincerely
> Ehsan
>
> On Wednesday, May 16, 2018, 8:23:32 AM GMT+4:30, Dennis Shea <
> shea at ucar.edu> wrote:
>
>
> This is book keeping. Something like:
>
> loop each year
> loop each month
> loop each day
>
> sum all values occurring between 00:00 and 11:59 inclusive
> ==>PRC(time,lat,lon,0)
> sum all values occurring between 12:00 and 23:59 inclusive
> ==>PRC(time,lat,lon,1)
>
> end day
> end month
> end year
>
>
> On Sun, May 13, 2018 at 9:07 AM, Ehsan Taghizadeh <
> ehsantaghizadeh at yahoo.com> wrote:
>
> Hi every body;
> Could I have any help to get daily precipitation from Era-Interim, please?
> I mean, a way to sum "accumulated precipitation from 00:00 to 12:00" with
> "accumulated precipitation from 12:00 to 24:00"?
>
> Sincerely
> Ehsan
>
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