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pslec

Computes sea level pressure from CCM/CAM hybrid model variables using the ECMWF formulation.

Prototype

	function pslec (
		t    [*][*] : numeric,  
		phis [*][*] : numeric,  
		ps   [*][*] : numeric,  
		pres [*][*] : numeric   
	)

	return_val [dimsizes(ps)] :  numeric

Arguments

t

A two-dimensional array containing temperatures (K) at the lowest model level. The two dimensions must be lat and lon.

phis

A two-dimensional array containing surface geopotential (m^2/s^2). Same dimensionality as t.

ps

A two-dimensional array equal to the surface pressure (Pa). Same dimensionality as t.

pres

A two-dimensional array containing pressures (Pa) of the lowest model level. Same dimensionality as t.

Return value

A multi-dimensional array (nlat,mlon) Double if any of the input arguments is double, float otherwise.

Description

Computes sea level pressure using the ECMWF formulation. The underlying code was taken directly from an old model post-processor that ran only on NCAR's Cray computers. It was developed for the 'old' CCM (Community Climate Model) hybrid model because the CCM did not output a sea level pressure variable. Also, at that time, the surface geopotential was constant. This function may be used with CAM hybrid model variables. However, generally, the CAM outputs the sea level pressure variable (PSL) and that should be used.

See Also

pslhyp, pslhor

Examples

Example 1 Derive sea level pressure from CCM/CAM hybrid level variables. The image produced by the following code may be viewed here .


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

  diri = "./"
  fili = "ccsm35.h0.0021-01.demo.nc"                ; CAM hybrid model
  f    = addfile(diri+fili,"r") 

  t    = f->T      ; (time,lev,lat,lon), [K]
  phis = f->PHIS   ; (time,lat,lon), [m2/s2]
  ps   = f->PS     ; (time,lat,lon), [Pa]

                   ; calculate pressures at each grid point and level
  hyam = f->hyam   ; read from a file the mid-layer coef
  hybm = f->hybm   ; read from a file
  p0   = f->P0 
  pres = pres_hybrid_ccm(ps,p0,hyam,hybm)  ; (ntim,klvl,nlat,lmon), [Pa]

                   ; get dimensions sizes
  dimt = dimsizes(t)
  ntim = dimt(0)
  klvl = dimt(1)
  nlat = dimt(2)
  mlon = dimt(3)

                   ; preallocate memory
  slp  = new( (/ntim,nlat,mlon/), typeof(ps), getFillValue(ps))

                   ; loop over all times. 'klvl-1' is the CCM/CAM lowest model level
  do nt=0,ntim-1
      slp(nt,:,:) = pslec(t(nt,klvl-1,:,:),phis(nt,:,:),ps(nt,:,:),pres(nt,klvl-1,:,:))
  end do

  copy_VarMeta(ps,slp)
  slp           = slp*0.01                  ; change units to hPa (not necessary)
  slp@long_name = "sea level pressure"
  slp@units     = "hPa"

  printVarSummary(slp)
  print("slp: min="+min(slp)+"  max="+max(slp))

;**********************************************t*
; plotting parameters
;************************************************
   wks  = gsn_open_wks("png","tst_pslec")       ; specifies a ps plot
   
   res                       = True     ; plot mods desired
   res@gsnMaximize           = True     ; affects ps, eps, pdf only
   res@mpFillOn              = False    ; no land gray fill
   res@cnFillOn              = True     ; turn on color
   res@cnLinesOn             = False    ; turn off contour lines
   res@gsnPaperOrientation   = "portrait"
  
   res@cnLevelSelectionMode  = "ManualLevels" 
   res@cnMinLevelValF        =   975.0
   res@cnMaxLevelValF        =  1040.0      
   res@cnLevelSpacingF       =     5.0     
   
   res@tiMainString          = "Test PSLEC"
  
   nt    = 0   ; plot slp at 1st time step
   plot  = gsn_csm_contour_map_ce(wks,slp(nt,:,:),res) ; create a default plot