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dpres_plevel_Wrap

Calculates the pressure layer thicknesses of a constant pressure level coordinate system.

Available in version 4.3.0 and later.

Prototype

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

	function dpres_plevel_Wrap (
		plev [*] : numeric,  
		psfc     : numeric,  
		ptop [1] : numeric,  
		iopt     : integer   
	)

	return_val  :  numeric

Arguments

plev

A one dimensional array containing the constant pressure levels. May be in ascending or descending order. Must have the same units as psfc.

psfc

A scalar or an array of up to three dimensions containing the surface pressure data in Pa or hPa (mb). The rightmost dimensions must be latitude and longitude. Must have the same units as plev.

ptop

A scalar specifying the top of the column. Must have the same units as plev.

iopt

Set to zero. Currently not used.

Return value

If psfc is a scalar the return variable will be a one-dimensional array the same size as plev; if psfc is two-dimensional [e.g. (lat,lon)] or three-dimensional [e.g. (time,lat,lon)] then the return array will have an additional level dimension: (lev,lat,lon) or (time,lev,lat,lon). The size of the lev dimension is the same as the size of plev. The returned type will be double if psfc is double, float otherwise.

Description

Calculates the layer pressure thickness of a constant pressure level system. It is analogous to dpres_hybrid_ccm for hybrid coordinates. At each grid point the sum of the pressure thicknesses equates to [psfc-ptop]. At each grid point, the returned values above ptop and below psfc will be set to psfc@_FillValue. If there is no psfc@_FillValue then the _FillValue will be set to 1e20. If ptop or psfc is between plev levels then the layer thickness is modifed accordingly. If psfc is set to _FillValue, all layer thicknesses are set to the appropriate _FillValue.

The primary purpose of this function is to return layer thicknesses to be used to weight observations for integrations.

Examples

Example 1 Consider a rawindsonde sounding and it is desired to compute the "internal energy" which is an integrated quantity.

                             ; PRESSURE (hPa)
  plev = (/ 1000.,950.,900.,850.,800.,750.,700.,650.,600., \
             550.,500.,450.,400.,350.,300.,250.,200., \
             175.,150.,125.,100., 80., 70., 60., 50., \
              40., 30., 25., 20. /)

                             ; TEMPERATURE (C)   
  t    =(/29.3,28.1,23.5,20.9,18.4,15.9,13.1,10.1, 6.7, 3.1,   \
          -0.5,-4.5,-9.0,-14.8,-21.5,-29.7,-40.0,-52.4,   \
         -59.2,-66.5,-74.1,-78.5,-76.0,-71.6,-66.7,-61.3, \
         -56.3,-51.7,-50.7,-47.5 /)

  plev       = plev*100.        
  plev@units = "Pa"        ; Pa   =  kg/(m s2) (Pascal)

  t          = t+273.15         
  t@units    = "K"
         
  ptop       = min(plev)    

  psfc       = 1018*100.           
  psfc@units = "Pa" 

  dp   = dpres_plevel(plev, psfc, ptop, 0)  ; dp(30)
  print("dp="+dp+"    t="+t)

  CP = 1004.               ; J/(K kg)     [ m2/(K s2) ] 
  GR = 9.81                ; gravity      [ m/s2 ]
  
  
                           ; integrate vertically
  IE   = (CP/GR)*sum( t*dp )  

  IE@long_name = "Internal Energy: Cp*sum( T*dp )/gravity"
  IE@units     = "kg/s2"
                           ; (for fun) weighted vertical average
  IE_average   = IE/sum(dp)  
  IE_average@long_name = "Internal Energy: Weighted vertical average"

The output from the print statement is:

        psfc=101800
(0)     plev=100000 dp=4300    t=302.45
(1)     plev=95000  dp=5000    t=301.25
(2)     plev=90000  dp=5000    t=296.65
(3)     plev=85000  dp=5000    t=294.05
(4)     plev=80000  dp=5000    t=291.55
(5)     plev=75000  dp=5000    t=289.05
(6)     plev=70000  dp=5000    t=286.25
(7)     plev=65000  dp=5000    t=283.25
(8)     plev=60000  dp=5000    t=279.85
(9)     plev=55000  dp=5000    t=276.25
(10)    plev=50000  dp=5000    t=272.65
(11)    plev=45000  dp=5000    t=268.65
(12)    plev=40000  dp=5000    t=264.15
(13)    plev=35000  dp=5000    t=258.35
(14)    plev=30000  dp=5000    t=251.65
(15)    plev=25000  dp=5000    t=243.45
(16)    plev=20000  dp=3750    t=233.15
(17)    plev=17500  dp=2500    t=220.75
(18)    plev=15000  dp=2500    t=213.95
(19)    plev=12500  dp=2500    t=206.65
(20)    plev=10000  dp=2250    t=199.05
(21)    plev=8000   dp=1500    t=194.65
(22)    plev=7000   dp=1000    t=197.15
(22)    plev=7000   dp=1000    t=197.15
(23)    plev=6000   dp=1000    t=201.55
(24)    plev=5000   dp=1000    t=206.45
(25)    plev=4000   dp=1000    t=211.85
(26)    plev=3000   dp=750     t=216.85
(27)    plev=2500   dp=500     t=221.45
(28)    plev=2000   dp=750     t=222.45
(29)    plev=1000   dp=500     t=225.65



Variable: IE
Type: float
Total Size: 4 bytes
            1 values
Number of Dimensions: 1
Dimensions and sizes:   [1]
Coordinates: 
Number Of Attributes: 2
  units :       W/m2
  long_name :   Internal Energy: Cp*sum( T*dp )/gravity
(0)     2.72987e+09

Example 2 Consider a similar but more common usage. Read data from an ERA-40 (or NCEP) data set. Compute Latent heat energy.

    f   = addfile ("foo.ERA40.nc" , "r")
    lev = f->lev  ; (/  1,  2,  3,  5,   7, 10, 20, 30, \ 
                  ;    50, 70,100,150, 200,250,300,400, \
                  ;   500,600,700,775, 850,925,1000 /)

    Q   = f->Q    ; kg/kg      (time,lev,lat,lon)
    psfc= f->PS   ; PA         (time,lat,lon)

    lev = lev*100
    lev@units = "Pa"    ; to match PS

    ptop= 0             ; integrate 0==>psfc at each grid point

                        ; dp(ntim,klev,nlat,mlon)
    dp  = dpres_plevel(lev, psfc, ptop, 0)

                        ; latent heat of vaporization at 0C
    L   = 2.5e6         ; J/kg         [ m2/s2 ]
    g   = 9.81          ; m/s
    
    
    Qdp = Q*dp          ; temporary variable
    copy_VarCoords(Q, Qdp)

                        ; integrate vertically [level dimension = 1] 
    LE  = dim_sum_n_Wrap( Qdp,1 )   ; LE(ntim,nlat,mlon)
    LE  = (L/GR)*LE     ; (time,lat,lon)
    LE@long_name = "Latent Energy:  SUM[L*Q*dp]/g"
    LE@units     = "kg/s2"

    printVarSummary( LE )

    delete( Qdp )    ; no longer needed

Example 3: version 5.1.0 and earlier

Same as Example 2 but use dimension reordering so that "lev" is the rightmost dimension.