NCL Home > Documentation > Functions > WRF, Interpolation


Interpolates a horizontal slice from a three-dimensional WRF-ARW field at the given vertical level(s).

Available in version 6.6.0 and later.


load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"      ; These two libraries are automatically
load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"    ; loaded from NCL V6.4.0 onward.
                                                              ; No need for user to explicitly load.

	function wrf_user_interp_level (
		var3d           : numeric,  
		vert            : numeric,  
		desired_levels  : numeric,  
		opt         [1] : logical   

	return_val  :  numeric



A WRF-ARW field to be interpolated; it must have at least three dimensions, with the rightmost dimensions being level x latitude x longitude.


An array of vertical coordinates for var3d, typically pressure or height. The dimensionality must be the same as var3d.

If vert is pressure, the units may be either hPa or Pa. If vert is height, then the units of the field must be in m.


The desired vertical level(s). This can be a single value (e.g. 500), a sequence of values (e.g. (/1000, 850, 700, 500, 250/)), or a multi-dimensional array where the rightmost two dimensions (lat x lon) must match var3d, and any leftmost dimensions match field3d's (e.g. planetary boundary layer). Must be in the same units as the vert parameter.


A logical scalar that can optionally contain attributes. See description below.


This function interpolates a WRF-ARW variable to a horizontal plane at the specified vertical level, which can be in height or pressure coordinates. This function combined with wrf_user_vert_cross replaces wrf_user_intrp3d, which will be deprecated in NCL V6.6.0.

There's currently only one optional attribute available via opt:

  • inc2dlevs - If set to True, then the return value will have an attribute called level that is set to the value of the input parameter desired_levels

See Also

wrf_user_interp_line, wrf_user_vert_cross


Example 1: Interpolate the given 3D field at pressure = 500 hPa.

  a = addfile("wrfout_d03_2012-04-22_23_00_00","r")

  time = 0    ; first time step
  ht     = wrf_user_getvar(a, "z",time)          ; grid point height
  p      = wrf_user_getvar(a, "pressure",time)   ; total pressure
  ht_500 = wrf_user_interp_level(ht,p,500,False)

  printVarSummary(ht)      ; [bottom_top | 31] x [south_north | 546] x [west_east | 480]
  printVarSummary(ht_500)  ; [south_north | 546] x [west_east | 480]


  Variable: ht
  Type: float
  Total Size: 32497920 bytes
              8124480 values
  Number of Dimensions: 3
  Dimensions and sizes : [bottom_top | 31] x [south_north | 546] x [west_east | 480]
  Number Of Attributes: 6
  coordinates : XLONG XLAT
  stagger : 
  units : m
  description : Height
  MemoryOrder : XYZ
  FieldType : 104
  Variable: ht_500
  Type: float
  Total Size: 1048320 bytes
              262080 values
  Number of Dimensions: 2
  Dimensions and sizes: [south_north | 546] x [west_east | 480]
  Number Of Attributes: 5
  description : Height
  units : m
  level : 500
  _FillValue : 9.96921e+36
  level_units : hPa