Re: How to find the Relative humidity if we take only 4 pressure levels?

From: Dennis Shea <shea_at_nyahnyahspammersnyahnyah>
Date: Fri Nov 25 2011 - 08:00:34 MST

The values are 'wrong' because ....

While you printed out the variable overview (printVarSummary),
you did not look at what you printed (ie, variable structure).
The variable consists of spherical harmonic complex coefficients.
Note the "real_imaginary" dimension of size 2 [real and complex].

> initial_time0_hours = 31 ;
> lv_ISBL1 = 4 ;
> real_imaginary = 2 ; <=== complex coefficients
> g50_lat_3 = 800 ; <=== size of complex coef array
> g50_lon_4 = 800 ;
[snip]
> float R_GDS50_ISBL(initial_time0_hours, lv_ISBL1, real_imaginary,
g50_lat_3, g50_lon_4)

Before using any variable with a "real_imaginary" dimension,
the coefficients must be used to reconstruct ['synthesize']
the original variable.

===
Somebody used 'ncl_convert2nc' because the file attribute says
   title = "NCL: convert-GRIB-to-netCDF

If using NCL, there is no need to perform this conversion.
The grib file can be used directly in addfile.
===

ALso ... I do not know what you are using for weights
but they should be layer thickness. See:

http://www.ncl.ucar.edu/Document/Functions/Built-in/dpres_plevel.shtml
The bottom should be sfc pressure but you do not gave it on the file.

     ptop thickness weight (dp)
                            (700-ptop)
     700
               750
     800 75
               825
     850 50
               875
     900 (pbot-875)

     pbot

Also, the vertical average is

     rh_dp = dim_sum_wgt_n(RH,dp,0,1)/sum(dp) ; SUM(RH*dp)/SUM(dp)

=======================================================
The attached may work. I do not have your file so you may have to change
the code.

It is YOUR responsibility to read the documentation
of all of the functions used;
use print statements and **look** at the output.

Good luck

On 11/23/11 10:47 PM, Manaswini Sreekar wrote:
> Hi
>
> I am new to NCL.
>
> Is there anyone who can provide the hint to calculate the Weighted
> average of relative humidity?
>
> I am getting the errors as
>
> fatal:dim_avg_wgt_n: w must be length nx
> fatal:Execute: Error occurred at or near line 15 in file CFRHC.ncl
>
> The min and max values for relative humidity are min(RH)=-20.4056
> max(RH)=213.099.
>
> Are these values are correct or wrong?
>
>
>
> The Print VarSummary
>
> Variable: RH_TL_AVG
> Type: float
> Total Size: 317440000 bytes
> 79360000 values
> Number of Dimensions: 4
> Dimensions and sizes: [g50_lat_3 | 800] x [g50_lon_4 | 800] x
> [initial_time0_hours | 31] x [lv_ISBL1 | 4]
> Coordinates:
> initial_time0_hours: [1827654..1828374]
> lv_ISBL1: [700..900]
> Number Of Attributes: 10
> center : European Center for Medium-Range Weather Forecasts (RSMC)
> long_name : Relative humidity
> units : %
> _FillValue : 1e+20
> level_indicator : 100
> gds_grid_type : 50
> parameter_table_version : 128
> parameter_number : 157
> forecast_time : 0
> forecast_time_units : hours
>
> The net CDF file
>
> manaswini@nature:~/Desktop$ ncdump -c RH.nc
> netcdf RH {
> dimensions:
> initial_time0_hours = 31 ;
> lv_ISBL1 = 4 ;
> real_imaginary = 2 ;
> g50_lat_3 = 800 ;
> g50_lon_4 = 800 ;
> ncl_strlen_0 = 18 ;
> variables:
> char initial_time0(initial_time0_hours, ncl_strlen_0) ;
> initial_time0:NCL_converted_from_type = "string" ;
> initial_time0:units = "mm/dd/yyyy (hh:mm)" ;
> initial_time0:long_name = "Initial time of first record" ;
> int lv_ISBL1(lv_ISBL1) ;
> lv_ISBL1:units = "hPa" ;
> lv_ISBL1:long_name = "isobaric level" ;
> double initial_time0_encoded(initial_time0_hours) ;
> initial_time0_encoded:units = "yyyymmddhh.hh_frac" ;
> initial_time0_encoded:long_name = "initial time encoded as
> double" ;
> double initial_time0_hours(initial_time0_hours) ;
> initial_time0_hours:units = "hours since 1800-01-01 00:00" ;
> initial_time0_hours:long_name = "initial time" ;
> float R_GDS50_ISBL(initial_time0_hours, lv_ISBL1, real_imaginary,
> g50_lat_3, g50_lon_4) ;
> R_GDS50_ISBL:forecast_time_units = "hours" ;
> R_GDS50_ISBL:forecast_time = 0 ;
> R_GDS50_ISBL:parameter_number = 157 ;
> R_GDS50_ISBL:parameter_table_version = 128 ;
> R_GDS50_ISBL:gds_grid_type = 50 ;
> R_GDS50_ISBL:level_indicator = 100 ;
> R_GDS50_ISBL:_FillValue = 1.e+20f ;
> R_GDS50_ISBL:units = "%" ;
> R_GDS50_ISBL:long_name = "Relative humidity" ;
> R_GDS50_ISBL:center = "European Center for Medium-Range Weather
> Forecasts (RSMC)" ;
>
> // global attributes:
> :creation_date = "Mon Nov 21 17:44:39 IST 2011" ;
> :NCL_Version = "6.0.0-beta" ;
> :system = "Linux nature 2.6.31-23-generic #75-Ubuntu SMP Fri
> Mar 18 18:16:06 UTC 2011 x86_64 GNU/Linux" ;
> :conventions = "None" ;
> :grib_source = "RH.grib" ;
> :title = "NCL: convert-GRIB-to-netCDF" ;
> data:
>
> lv_ISBL1 = 700, 800, 850, 900 ;
>
> initial_time0_hours = 1827654, 1827678, 1827702, 1827726, 1827750,
> 1827774,
> 1827798, 1827822, 1827846, 1827870, 1827894, 1827918, 1827942,
> 1827966,
> 1827990, 1828014, 1828038, 1828062, 1828086, 1828110, 1828134,
> 1828158,
> 1828182, 1828206, 1828230, 1828254, 1828278, 1828302, 1828326,
> 1828350,
> 1828374 ;
> }
> manaswini@nature:~/Desktop$ ^C
>
>
>
>
>
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Received on Fri Nov 25 08:00:41 2011

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