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pot_vort_hybrid

Compute potential vorticity on hybrid levels and a global grid.

Available in version 6.3.0 and later.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"  ; This library is automatically loaded
                                                             ; from NCL V6.2.0 onward.
                                                             ; No need for user to explicitly load.

	function pot_vort_hybrid (
		p            : numeric,  
		u            : numeric,  
		v            : numeric,  
		t            : numeric,  
		lat      [*] : numeric,  
		gridType [1] : integer,  
		opt          : integer   
	)

	return_val [dimsizes(t)] :  float or double

Arguments

p

Array containing pressure levels. Must be (lev,lat,lon) or (time,lev,lat,lon)

u

Array containing zonal wind components (m/s). Same size and shape as p.

v

Array containing meridional wind components (m/s). Same size and shape as p.

t

Array containing temperatures (K). Same size and shape as p.

gridType

Grid type. gridType=0 means gaussian grid; gridType=1 means regular or fixed grid.

opt

  • opt=0: return potential vorticity
  • opt=1: return a list variable containing: potential vorticity, static stability, potential temperature

Return value

A multi-dimensional array of the same size and shape as t. The output will be double if t is of type double.

Description

Calculate the potential vorticity on hybrid levels on a global grid. The reason for the global grid is that highly accurate spherical harmonic functions are used to compute horizontal gradients. 


Reference:
    Compute Isentropic Potential Vorticity on hybrid levels
    CCM Processor User's Guide: May 1994: page B-19
    Original source P Rasch and B Boville

Note: A nice basic discussion of PV may be found at:
Mid-Latitude Atmospheric Dynamics: A First Course
Jonathan E. Martin, Wiley 2006,   QC880.M36   , pp276-onward

See Also

pot_vort_isobaric, static_stability, pot_temp

Examples

Worked examples are HERE.

Example 1 


     f    = addfile("foo.nc", "r")
     U    = f->U   ; (time,lev,lat,lon) or (lev,lat,lon)
     V    = f->V
     T    = f->T
     lat  = f->lat

     hyam = f->hyam
     hybm = f->hybm
     p0   = f->P0  ; p0=100000
     ps   = f->PS  ; Pa
     p    = pres_hybrid_ccm (ps,p0,hyam,hybm)  ; Pa [kg/(m s2)]
     copy_VarCoords(U,p)
  
     gridType = 0  ; gaussian grid   
                   ; Potential Vorticity
     PV = pot_vort_hybrid(p,u,v,t,lat, gridType,  0)
Example 2 Here the data are ordered north to south. Most reanalysis data sets are ordered north to south. Use NCL syntax to reorder the data. 

     f    = addfile ("foo.nc", "r")
     U    = f->U    ; (time,lev,lat,lon) or (lev,lat,lon)
     V    = f->V
     T    = f->T

     U    = U(:,:,::-1,:)    ; reorder to South -> North
     V    = V(:,:,::-1,:)
     T    = T(:,:,::-1,:)
     
     lat  = T&lat
     gridType  = 1          ; fixed grid
     opt = 0

     hyam = f->hyam
     hybm = f->hybm
     p0   = f->P0  ; p0=100000
     ps   = f->PS  ; Pa
     p    = pres_hybrid_ccm (ps,p0,hyam,hybm)  ; Pa [kg/(m s2)]
     copy_VarCoords(U,p)
  

     PV = pot_vort_hybrid(lev,u,v,t,lat, gridType, opt)   ; Potential Vorticity