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pres2hybrid_Wrap

Interpolates data on constant pressure levels to hybrid levels and retains metadata.

Available in version 4.2.0.a034 and later.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"

	function pres2hybrid_Wrap (
		p      [*] : numeric,  
		ps         : numeric,  
		p0     [1] : numeric,  
		xi         : numeric,  
		hyao   [*] : numeric,  
		hybo   [*] : numeric,  
		intflg [1] : integer   
	)

	return_val  :  numeric

Arguments

A one dimensional array specifying the pressure levels. Must be top-to-bottom order and must have the same units as ps and p0.

A multi-dimensional array containing pressures. Must be at least two dimensions and one dimension smaller than xi. The level dimension is ordered top-to-bottom. Must have the same units as p0.

A scalar value equal to the surface reference pressure. Must have the same units as ps and p. Typically p0=100000 [Pa] or 1000 [hPa].

A multi-dimensional array containing the variable to be interpolated. The three rightmost dimensions must be (pressure) level, lat, and lon. The level dimension is ordered top-to-bottom.

hyao

A one-dimensional array containing the hybrid coefficients A associated with the return_val. Must be ordered top-to-bottom. Must be unitless.

hybo

A one-dimensional array containing the hybrid coefficients B associated with the return_val. Must be ordered top-to-bottom. Must be unitless.

intflg

A scalar integer which specifies the type of extrapolation to be used.

    =0   no extrapolation. Values set to _FillValue
    =1   values set to nearest valid value
    =2   values less than min(p) set to nearest value
         values greater than max(p) are linearly extrapolated 
    =3   values less than min(p) are linearly extrapolated
         values greater than max(p) set to nearest value 
    =4   values than min(p) are extrapolated
         values greater than max(p) are extrapolated

Return value

A multi-dimensional array of the same size as xi except that the level dimension has been replaced by the size of hyao. Double if xi or ps are double, float otherwise.

Description

Interpolates from data on constant pressure levels to a set of hybrid levels.

The basic approach is to calculate the pressure at each level for the output hybrid levels. Then interpolate the input variable to the pressures of the desired output hybrid levels.

At each latitude, longitude and level (lev[k]) pressures are computed using:

             p(k) = A(k)*PO + B(k)*PS            (1)

This is the form used by the Community Atmosphere Model (CAM) and it is the form expected by pres2hybrid_Wrap. A visualization of the hybrid coordinate system is here. Typically, the A and B coefficients might have values like:

  A = 0.0048093, 0.0130731, 0.0325591, 0.0639471, 0.0816768, 0.0780201, 
      0.0733671, 0.0676476, 0.0608624, 0.0531095, 0.0445995, 0.0356607, 
      0.0267266, 0.0183069, 0.0109421, 0.005147 , 0.0013519, 0 ;

  B = 0, 0, 0, 0, 0.0173664, 0.0606928, 0.1158237, 0.1835918, 0.2639851, 
      0.3558459, 0.456676, 0.5625875, 0.6684428, 0.768203, 0.8554653, 
      0.9241285, 0.9690938, 0.9925282 ;

If the "A" and "B"coefficients are different from (1) then it is the users responsibility to make the appropriate changes. For example, an alternative form of (1) is:

             p(k) = AP(k) + B(k)*PS             (2)

In this form, each AP coefficient AP(k)=A(k)*PO. In this case the value of p0 input to pres2hybrid_Wrap should be set to one [1.0].

This function is identical to the built-in function pres2hybrid, except it retains metadata.

Examples

Example 1

This example interpolates a variable from ECMWF's 23 pressure levels to a set of hybrid levels (26 here).


   diri = "./"
   filC = "sstclimt42_run01.cam2.h0.0001-01.nc"    ; CAM
   filT = "e4oper.an.pl.t85.t.198501"              ; ECMWF pressure level dataset
   filP = "e4moda.an.ml.t85.psfc.1985.nc"          ; ECMWF surface pressure 

   f    = addfile (diri+filT, "r")
   tp   = f->T                                     ; variable to be interpolated
   fP   = addfile (diri+filP, "r")
   psfc = fP->PSFC                                 ; surface pressure (Pa)
   p0   = 100000.                                  ; reference pressure (Pa)

   fC   = addfile (diri+filC, "r")
   hya  = fC->hyam                                 ; levels to which the variable
   hyb  = fC->hybm                                 ; will be interpolated

   plev = tp@lev                                   ; hPa
   plev = plev*100.                                ; match units of p0 and psfc
   plev@units = "Pa"

   th   = pres2hybrid_Wrap(plev,psfc,p0,tp,hya,hyb,0)          ; temperature on hybrid levels

If the input variable looks like:

          Variable: tp
          Type: float
          Total Size: 373817344 bytes
                      93454336 values
          Number of Dimensions: 4
          Dimensions and sizes:   [time | 124] x  [lev | 23] x [lat | 128] x [lon | 256]
          Coordinates: 
                      time: [1621680..1622418]
                      lev: [1..1000]                      ; note these are hPa
                      lat: [-88.92773..88.92773]
                      lon: [ 0..358.53]
          Number Of Attributes: 3
            standard_name :       air_temperature
            units :       K
            long_name :   Temperature

The output variable will look like:

          Variable: th
          Type: float
          Number of Dimensions: 4
          Dimensions and sizes:   [time | 124] x  [lev | 26] x [lat | 128] x [lon | 256]
          Coordinates: 
                      time: [1621680..1622418]
                      lev: [4.8093..992.5282]            ; 'nominal' pressures
                      lat: [-88.92773..88.92773]
                      lon: [ 0..358.53]
          Number Of Attributes: 3
            standard_name :       air_temperature
            units :       K
            long_name :   Temperature