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pot_vort_isobaric

Compute potential vorticity on isobaric levels and a global rectilinear 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_isobaric (
		p        [*] : numeric,  
		u            : numeric,  
		v            : numeric,  
		t            : numeric,  
		lat      [*] : numeric,  
		gridType [1] : integer,  
		opt      [1] : integer   
	)

	return_val [dimsizes(t)] :  float or double

Arguments

p

Array containing pressure (Pa) levels. Must be 1D (lev)

u

Array containing zonal wind components (m/s). Must be 3D (lev,lat,lon) or 4D (time,lev,lat,lon). The array must be ordered south to north.

v

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

t

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

lat

Latitudes ordered south to north for the rectilinear grid.

gridType

Grid type: gridType=0 means gaussian grid; gridType=1 means regular or fixed grid. Both are rectilinear grids.

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

References: 
     Bluestein: Synoptic-Dynamic Meteorology in Midlatitudes pg 264  Eq 4.5.93

     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_hybrid, static_stability, pot_temp,

Examples

Note: The dimension names are those used by the CESM. NCL does not care what the dimensions are named.

Worked potential vorticity examples are HERE.

Example 1: Here the data are south to north. 


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

     lev = f->lev  ; hPa
     lev = lev*100 ; convert units
     lev@units = "Pa"

     gridType  = 0       ; gaussian grid
     opt = 0
     PV = pot_vort_isobaric(lev,u,v,t,lat, gridType, opt)
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) 
     V   = f->V
     T   = f->T    ; K

     lev = f->lev  ; hPa
     lev = lev*100 ; convert units
     lev@units = "Pa"

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

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