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vinth2p_ecmwf

Interpolates CESM hybrid coordinates to pressure coordinates but uses an ECMWF formulation to extrapolate values below ground.

Prototype

	function vinth2p_ecmwf (
		datai      : numeric,  
		hbcofa [*] : numeric,  
		hbcofb [*] : numeric,  
		plevo  [*] : numeric,  
		psfc       : numeric,  
		intyp  [1] : integer,  
		p0     [1] : numeric,  
		ii     [1] : integer,  
		kxtrp  [1] : logical,  
		varflg [1] : integer,  
		tbot       : numeric,  
		phis       : numeric   
	)

	return_val  :  numeric

Arguments

datai

An array of at most five* dimensions. Needs to contain a level dimension in hybrid coordinates. The order of the dimensions is specific. The three right-most dimensions must be level,lat,lon [e.g. TS(time,lev,lat,lon) or TS(case,time,lev,lat,lon]. The order of the level dimension must be top-to-bottom.

* Note: this function was updated in version version 4.3.0 to allow datai to be 5 dimensions.

hbcofa

A one-dimensional array containing the hybrid A coefficients. Must have the same dimension as the level dimension of datai. The order must be top-to-bottom. (These are expected to be normalized to one (1.0). If not, divide by P0.)

hbcofb

A one-dimensional array containing the hybrid B coefficients. Must have the same dimension as the level dimension of datai. The order must be top-to-bottom.

plevo

A one-dimensional array of output pressure levels in mb.

psfc

A multi-dimensional array of surface pressures in Pa. Must have the same dimension sizes as the corresponding dimensions of datai.

intyp

Scalar integer value equal to the interpolation type 1 - LINEAR, 2 - LOG, 3 - LOG LOG

p0

Scalar numeric value equal to surface reference pressure in Mb.

ii

Not used at this time. Set to 1.

kxtrp

Logical. False = no extrapolation when the pressure level is outside of the range of psfc.

varflg

A scalar integer indicating which variable to interpolate: 1 = temperature, -1 = geopotential height, 0 = all others.

tbot

A multi-dimensional array the same sizes as psfc equal to temperature at the lowest (i.e, closest to the surface) level. While this is used only if varflg=-1 (ie, geopotential height), it must still be provided for all cases.

phis

A multi-dimensional array of surface geopotential (m^2/sec^2) in which the rightmost two dimensions are the same as psfc.

Return value

A multi-dimensional array of the same size as datai except that the level coordinate has been replaced by plevo. The function automatically copies the metadata from datai to return_val.

The type of the output data will be double only if psfc and datai are of type double. Otherwise, the return type will be float.

Description

Interpolates CESM hybrid coordinates to pressure coordinates. The type of interpolation is currently a variant of transformed pressure coordinates with the interpolation type specified by intyp. All hybrid coordinate values are transformed to pressure values. If datai is on midlevels (interfaces), then hyam/hybm (hyai/hybi) coefficients should be input.

This is similar to the routine used within the CESM Processor. The mixture of Pa for psfc and mb for plevo and p0 is specified by that source routine.

This function differs from vinth2p in the method it uses to extrapolate to levels below psfc. It uses the ECMWF formulation as described in

Vertical Interpolation and Truncation of Model-Coordinate Data 
Trenberth, Berry, Buja 
[NCAR/TN-396, 1993].
in which special formulations are used for temperature and geopotential height below ground. All other variables are simply held constant below ground at the values from the lowest model level.

See Also

Use vinth2p if no extrapolation below ground for temperature and geopotential is desired.

Examples

CESM1.0 output files in CCM History Tape (CCMHT) format. These files may be read into NCL directly using addfile with a ".ccm" extension. Alternatively, these files may be converted to netCDF using ccm2nc. The reason for mentioning this is that there are differences. The netCDF files produced by ccm2nc or output directly from later versions of the model:

  1. have the reference pressure (P0) contained within the file while earlier files do not. In the latter case the user must explicitly provide that information.
  2. produce variables with level, latitude and longitude being the three rightmost (fastest varying) dimensions [e.g. TS(time,lev,lat,lon)]. The variables in CCMHT format are ordered differently [e.g. (lat,lev,lon) or (time,lat,lev,lon)]. It is therefore necessary to reorder the variable before input.
  3. have a time dimension while the CCMHT files may or may not have a time dimension.
Example 1 Use the ECMWF formulation to extrapolate below ground. The syntax T(:,nlev-1,:,:) extracts the temperatures from the lowest hybrid level of the model. tbot is a 3D array dimensioned(time,lat,lon).
  fccm = addfile ("dummy.nc" , "r")  
  hyam = f->hyam                    
  hybm = f->hybm
  PSFC = f->PS
  P0mb = 0.01*f->P0
  PHIS = f->PHIS                       ; surface geopotential [2D]

  T    = f->T                          ; temperature at hybrid levels
  Z    = f->Z3                         ; geo hgt at hybrid levels
  U    = f->U                          ; zonal wind
  
  tbot = T(:,nlev-1,:,:)               ; bot temp level [clarity]
 
  nlev = dimsizes(hyam)                ; number of vertical levels
                                       ; specify levels to be interpolated
  lev_p   = (/ 850., 700., 500., 300., 200. /)
  lev_p!0         = "lev_p"            ; variable and dimension name the same
  lev_p&lev_p     = lev_p              ; create coordinate variable
  lev_p@long_name = "pressure"         ; attach some attributes
  lev_p@units     = "hPa"
  lev_p@positive  = "down"
  
  intyp = 1                             ; 1=linear, 2=log, 3=log-log
  kxtrp = True                          ; True=extrapolate
  
  varflg = 1                           ; temperature is variable
  Tp     = vinth2p_ecmwf(T,hyam,hybm,lev_p,PSFC,intyp,P0mb, \
                 1,kxtrp,varflg,tbot,PHIS)
  varflg = -1                          ; geo pot hgt is variable [tbot is used]
  Zp     = vinth2p_ecmwf(Z, hyam,hybm, lev_p ,PSFC, intyp, P0mb, \
                 1,kxtrp,varflg,tbot,PHIS)
  varflg = 0                           ; not T or Z
  Up     = vinth2p_ecmwf(U,hyam,hybm,lev_p,PSFC,intyp,P0mb,\
                 1,kxtrp,varflg,tbot,PHIS)