[ncl-talk] how to plot divergent winds, divergence and velocity potential in one single plot?

Vyankatesh Manoj Mundhada vyankatesh at iiserb.ac.in
Wed Feb 21 02:20:22 MST 2018

```Hello,

I am new to NCL and I am trying to plot divergent winds (vectors),
divergence (contours) and velocity potential (contours) in a single plot
using velocities u and v only.

When i am trying to plot divergent velocities using the following script:

begin
;*************************************************
; open file and read in data: data are on a gaussian grid
;*************************************************
u    = f->u                 ; (time,lat,lon)
v    = f->v
d    = f->d
;*************************************************
; calculate divergence on a gaussian grid
;*************************************************
div = uv2dvG_Wrap(u,v)                ; u,v ==> divergence
div at long_name  = "Divergence"
div at units      = "s-1"
;*************************************************
; calculate velocity potential
;*************************************************
chi = ilapsG_Wrap ( div , 0)
chi = (/chi/1e8/)                     ; arbitrary scale
chi at long_name = "velocity potential"
chi at units     = "m/s"
;*************************************************
; calculate divergent wind component
; --
; note: the calculation uses a procedure, so memory
; must be preallocated.
;*************************************************
ud    = new ( dimsizes(u), float, u at _FillValue )
vd    = new ( dimsizes(v), float, v at _FillValue )

dv2uvg(div,ud,vd) ; div  ==> divergent  wind components

copy_VarCoords(u, ud )
copy_VarCoords(u, vd )
ud at long_name  = "Zonal Divergent Wind"
ud at units      = u at units
vd at long_name  = "Meridional Divergent Wind"
vd at units      = v at units
;*************************************************
; plot results
;*************************************************
wks  = gsn_open_wks("png","dv")             ; send graphics to PNG file
nc   = dimsizes(cmap(:,0))

res                          = True
res at gsnDraw                                 = False
res at gsnFrame                             = False
cnres1                                        = res
cnres2                                        = res
vcres                                            = res

cnres1 at cnFillOn           = True               ; color on
cnres1 at cnLinesOn          = False              ; turn off contour lines
cnres1 at cnFillPalette      = cmap(:nc-4,:)
cnres1 at tiMainString       = "Divergent Winds, Divergence and Velocity
Potential"
cnres1 at lbOrientation           = "vertical"

vcres at vcRefMagnitudeF     = 10.                 ; make vectors larger
vcres at vcRefLengthF        = 0.05              ; ref vector length
vcres at vcGlyphStyle        = "CurlyVector"      ; turn on curly vectors
vcres at vcMinDistanceF      = 0.012              ; thin the vectors
vcres at vcRefAnnoOrthogonalPosF  = -1.185         ; Move ref anno into plot
vcres at vcRefAnnoBackgroundColor = "Background"
vcres at vcRefAnnoString2On    = False
;vcres at vcRefAnnoSide                =    "Right"

;cnres2 at gsnCenterString    = "Chi scaled by 1e8"
cnres2 at cnFillOn                        = False
cnres2 at cnLinesOn                    = True

plot1 =
gsn_csm_vector_map(wks,0.001*ud(0,0,:,:),0.001*vd(0,0,:,:),vcres)
;plot2    =
gsn_csm_contour_map_overlay(wks,div(0,0,:,:),chi(0,0,:,:),cnres1,cnres2)

;overlay(plot2,plot1)

draw(plot1)
frame(wks)

end

Using this script, i am getting global plot and following error.

(0)    check_for_y_lat_coord: Warning: Data either does not contain a valid
latitude coordinate array or doesn't contain one at all.
(0)    A valid latitude coordinate array should have a 'units' attribute
equal to one of the following values:
(0)        'degrees_north' 'degrees-north' 'degree_north' 'degrees north'
'degrees_N' 'Degrees_north' 'degree_N' 'degreeN' 'degreesN' 'deg north'
(0)    check_for_lon_coord: Warning: Data either does not contain a valid
longitude coordinate array or doesn't contain one at all.
(0)    A valid longitude coordinate array should have a 'units' attribute
equal to one of the following values:
(0)        'degrees_east' 'degrees-east' 'degree_east' 'degrees east'
'degrees_E' 'Degrees_east' 'degree_E' 'degreeE' 'degreesE' 'deg east'

But when I am plotting all three together using the above script I am
getting no error and a global plot with velocity vectors showing only on
certain region. I am attaching both output png files.

Thanking you

-------------- next part --------------
An HTML attachment was scrubbed...
-------------- next part --------------
A non-text attachment was scrubbed...
Name: dv.png
Type: image/png
Size: 227289 bytes
Desc: not available