arbitrary cross-section

[Xuguang Sun]

*********************************************************************
* The following lines will display an arbitrary X
section
* from one specified point to another.
*
* lon1 is the westernmost longitude point
* lon2 is the easternmost longitude point
* lat1 is the latitude that corresponds to lon1
* lat2 is the latitude that corresponds to lon2
*
* The loop is used to interpolate between points in
* the arbitrary cross section. This code will plot
* any cross section as long as you specify the points.

* My code plots cross sections of PV after I
calculated
* PV on 11 pressure surfaces. I have another script
* that plots cross sections of potential temperature,
and
* the code is very similar to this, except theta is
substituted
* for PV.
*
* Many thanks to Brian Doty at COLA for his help with
this code.
*
********************************************************************
function cross_sec(args)

say 'Usage: cross_sec var lon1 lon2 x1 x2 lat1 lat2
lev1 lev2'
say '       var   ----   variable'
say '       lon1  ----   leftmost longitude'
say '       lon2  ----   rightmost longitude'
say '       x1    ----   leftmost x coordinate'
say '       x2    ----   rightmost x coordinate'
say '       lat1  ----   southmost latitude'
say '       lat2  ----   northmost latitude'
say '       lev1  ----   lowmost level'
say '       lev2  ----   highmost level'

var  =  subwrd(args,1)
lon1 =  subwrd(args,2)
lon2 =  subwrd(args,3)
x1   =  subwrd(args,4)
x2   =  subwrd(args,5)
lat1 =  subwrd(args,6)
lat2 =  subwrd(args,7)
lev1 =  subwrd(args,8)
lev2 =  subwrd(args,9)

if(var=''|lon1=''|lon2=''|x1=''|x2=''|lat1=''|lat2=''|lev1=''|lev2='');
say 'Incorrect input args';
return;
endif

'set grads off'
'set zlog on'
'set x 1'
'set y 1'
'set z 'lev1' 'lev2''
lon = lon1
'collect 1 free'
while (lon <= lon2)
  lat = lat1 + (lat2-lat1)*(lon-lon1) / (lon2-lon1)
  'collect 1 gr2stn('var','lon','lat')'
  lon = lon + 1
endwhile

'set x 'x1' 'x2''
'set xaxis 'lon1' 'lon2
'set clab on'
'set gxout shaded'
*'set clevs 0 .5 15'
*'set ccols 0 0 7 0'
'd coll2gr(1,-u)'
'set gxout contour'
*'set cint .5'
'd coll2gr(1,-u)'

return


SUN Xuguang
Department of Atmospheric Sciences
22 Hankou Road, Nanjing University, 210093
Nanjing, P.R.China

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