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shear_stretch_deform_cfd

Using centered-finite-differences, estimate the kinematic shear-deformation, stretch-deformation and total-deformation of a global or regional horizontal (east-west) wind field.

Available in version 6.6.2 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 shear_stretch_deform_cfd (
		u          : numeric,  
		v          : numeric,  
		lat    [*] : numeric,  
		lon    [*] : numeric,  
		cyclic [1] : logical,  
		opt    [1] : integer   
	)

	return_val [dimsizes(lat)] :  float or double

Arguments

u

Zonal wind component. Must be on a rectilinear grid ordered South-to-North.

v

Meridional wind component. Same size and shape as u.

lat

Latitudes (degrees).

lon

Longitudes (degrees).

cyclic

Grid type: cyclic=True means grid is cyclic in longitude; cyclic=False means grid is regional.

opt

  • opt=0 means return the shear, stretch and total deformation [3 variables]
  • opt=1 means return the shear, stretch, total deformation and the four gradient fields: du/dx, du/dy, dv/dx and dv/dy [7 variables].

Return value

A variable of type list containing variables of the same size and shape as u. The returned variables do not include any explicit negative (or positive) sign or coefficient (eg: 0.5). 

 
  shear   = dvdx + dudy
  stretch = dudx - dvdy
  deform  = sqrt(shear^2 + stretch^2)

Description

Divergence and vorticity are commonly used kinematic fields. Less commonly used are the shear-deformation (SHD) and stretch-deformation (STD). 

               SHD = dv/dx + du/dy
               STD = du/dx - dv/dy
When the stretch-deformation is negative/positive the flow is confluent/diffluent. Typically, the individual shear- and stretch-deformation components are less useful that the total-deformation (TD): 

               TD = sqrt(SVD^2 + STD^2)

This function should be used only on high frequency 3-, 6-hrly or daily mean data.

References: 

   Kinematic Propeerties: Synoptic Meteorology I: 2014

   Spensberger, C. and T. Spengler (2014) 
    A New Look at Deformation as a Diagnostic for Large-Scale Flow 
   J. Atmos. Sci

See Also

uv2vrG,uv2dvG, uv2vrF,uv2dvF, uv2vr_cfd,uv2dv_cfd, qvector_isobaric, qvector_isobaric_cfd

Examples

Example 1: Read in a region using NCL's coordinate subscripting. 


  latS   =  25.          ; region   
  latN   =  50.
  lonL   = 230.
  lonR   = 300.

  fuv    = addfile("...", "r")    
  u      = fuv->uwnd(:,:,{latS:latN},{lonL:lonR})   ; (time, level, lat, lon) ; level=17
  v      = fuv->vwnd(:,:,{latS:latN},{lonL:lonR})

  opt_ssd = 0      ; shear, stretch and total deformation only
  cyclic  = False  ; region
  ssdList = shear_stretch_deform_cfd(u,v, u&lat, u&lon, cyclic, opt_ssd)

  stretch_region = ssdList[0]    ; extract variables for clarity; append _region for clarity
  shear_region   = ssdList[1]
  deform_region  = ssdList[2]

  delete(ssdList) ; not required;   just not needed anymore

  printVarSummary(stretch_region)
  printMinMax(stretch_region,0)
  
  printVarSummary(shear_region)
  printMinMax(shear_region,0)

  printVarSummary(deform_region)
  printMinMax(deform_region,0)
The (edited) output: 

          Variable: stretch_region
          Type: float
          Total Size: 151844 bytes
                      37961 values
          Number of Dimensions: 4
          Dimensions and sizes:   [time | 7] x [level | 17] x [lat | 11] x [lon | 29]
          Coordinates: 
                      time: [1823280..1823424]
                      level: [1000..10]
                      lat: [25..50]
                      lon: [230..300]
          Number Of Attributes: 4
            _FillValue :  -9.96921e+36
            long_name :   (dudx-dvdy): CFD
            units :       1/s
            NCL_tag :     shear_stretch_deform_cfd

          (0)     (dudx-dvdy): CFD (1/s) : min=-7.31857e-05   max=0.000132413
          (0)     ===
          
          Variable: shear_region
          Type: float
          Total Size: 151844 bytes
                      37961 values
          Number of Dimensions: 4
          Dimensions and sizes:   [time | 7] x [level | 17] x [lat | 11] x [lon | 29]
          Coordinates: 
                      time: [1823280..1823424]
                      level: [1000..10]
                      lat: [25..50]
                      lon: [230..300]
          Number Of Attributes: 4
            _FillValue :  -9.96921e+36
            long_name :   (dvdx+dudy): CFD
            units :       1/s
            NCL_tag :     shear_stretch_deform_cfd

          (0)     (dvdx+dudy): CFD (1/s) : min=-9.8741e-05   max=7.93867e-05
          (0)     ===
          
          Variable: deform_region
          Type: float
          Total Size: 151844 bytes
                      37961 values
          Number of Dimensions: 4
          Dimensions and sizes:   [time | 7] x [level | 17] x [lat | 11] x [lon | 29]
          Coordinates: 
                      time: [1823280..1823424]
                      level: [1000..10]
                      lat: [25..50]
                      lon: [230..300]
          Number Of Attributes: 5
            _FillValue :  -9.96921e+36
            long_name :   deformation
            units :       1/s
            information : sqrt[shear^2 + stretch^2 ]
            NCL_tag :     shear_stretch_deform_cfd

          (0)     deformation (1/s) : min=6.17707e-08   max=0.000132802