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hyi2hyo

Interpolates from data on one set of hybrid levels to another set of hybrid levels.

Prototype

	function hyi2hyo (
		p0     [1] : numeric,  
		hyai   [*] : numeric,  
		hybi   [*] : numeric,  
		ps         : numeric,  
		xi         : numeric,  
		hyao   [*] : numeric,  
		hybo   [*] : numeric,  
		intflg [1] : integer   
	)

	return_val  :  numeric

Arguments

A scalar value equal to the surface reference pressure. Must have the same units as ps.

hyai

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

hybi

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

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 multi-dimensional array containing the variable to be interpolated. The three rightmost dimensions must be 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. A value of 0 will cause all values outside of input pressure range to be set to xi's missing value (if xi has none, then 1e20 is used for V5.2.1 and earlier or the default missing for float/double is used for V6.0.x and higher). A value of 1 will set output values to the closest input pressure level.

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A multi-dimensional array of the same size as xi except that the level dimension has been replaced by the size of hyao.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. float.

Description

Interpolates from data on one set of hybrid levels to another set of hybrid levels. It is assumed that hyai, hyab, ps and xi are from the same source.

The basic approach is to calculate the pressures at each level for the input and output hybrid levels. Then interpolate in the input variable to the pressures of the desired output hybrid levels. Log-linear interpolation is used.

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 hyi2hyo. 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 hyi2hyo should be set to one [1.0].

Use the hyi2hyo_Wrap function if metadata retention is desired. The interface is identical.

Examples

Example 1

This example interpolates a variable from ECMWF's 60 hybrid level model to a different set of hybrid levels (26 here).


   diri = "./"
   filC = "sstclimt42_run01.cam2.h0.0001-01.nc"    ; CAM
   filU = "e4moda.an.ml.t85.u.1985.nc"             ; ECMWF [ds126.2]
   filP = "e4moda.an.ml.t85.psfc.1985.nc"          ; ECMWF [ds126.2]

   f    = addfile (diri+filU, "r")
   hyai = f->hyam                                  ; midlayer coef
   hybi = f->hybm
   ui   = f->U                                     ; variable to be interpolated
   p0   = f->P0                                    ; reference pressure (Pa)
   fP   = addfile (diri+filP, "r")
   psfc = fP->PSFC                                 ; surface pressure (Pa)

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

   uo   = hyi2hyo(p0,hyai,hybi,psfc,ui,hyao,hybo,0)

   ; Use hyi2hyo_Wrap if metadata retention is desired
   ; uo   = hyi2hyo_Wrap(p0,hyai,hybi,psfc,ui,hyao,hybo,0)

If the input variable looks like:

          variable: ui
          Type: float
          Total Size: 94371840 bytes
                      23592960 values
          Number of Dimensions: 4
          Dimensions and sizes:   [time | 12] x  [lev | 60] x [lat | 128] x [lon | 256]
         Coordinates: 
                      time: [1621680..1629696]
                      lev: [1e-06..998.8151]
                      lat: [-88.92773..88.92773]
                      lon: [ 0..358.53]
          Number Of Attributes: 4
            long_name :   U velocity
            units :       m/s
            standard_name :       eastward_wind
            cell_method : time: mean

The output variable will look like: