求偏dp/偏t

ZMZ

用grads对变量dp求局地变化率 偏dp/偏t ，用中央差分法计算，各位大神看看对不对

'set fwrite /sky3/zhangmz20/data/ddpt298.dr'
'set gxout fwrite'
t=2
'define ddpt=0'
while (t<=1580)
'set z 3'
'set lon 100 140'
'set lat 20 50'
'set t 't-1
'define dp1=dp'
'set t 't+1
'define dp2=dp'
'define ddpt=(dp2-dp1)/2'
'd ddpt'
t=t+1
endwhile
'disable fwrite'

ZMZ

求各位大神帮帮忙&#129402;

river

给你个函数参考

cdiff
cdiff(expr,dim)

Performs a centered difference operation on expr in the direction specified by dim. The difference is done in the grid space, and no adjustment is performed for unequally spaced grids. The result value at each grid point is the value at the grid point plus one minus the value at the grid point minus one. The dim argument specifies the dimension over which the difference is to be taken, and is a single character: X, Y, Z, or T.

Result values at the grid boundaries are set to missing.

Usage Notes
Examples
The cdiff function may be used to duplicate the calculation done by the hcurl function:
define dv = cdiff(v,x)
define dx = cdiff(lon,x)*3.1416/180
define du = cdiff(u*cos(lat*3.1416/180),y)
define dy = cdiff(lat,y)*3.1416/180
display (dv/dx-du/dy)/(6.37e6*cos(lat*3.1416/180))
The above example assumes an X-Y varying dimension environment. Note that the intrinsic variables lat and lon give results in degrees and must be converted to radians in the calaculation. Also note the radius of the earth is assumed to be 6.37e6 meters thus the U and V winds are assumed to have units of m/sec.

Temperature advection can be calculated using the cdiff function as follows:
define dtx = cdiff(t,x)
define dty = cdiff(t,y)
define dx = cdiff(lon,x)*3.1416/180
define dy = cdiff(lat,y)*3.1416/180
display -1*( (u*dtx)/(cos(lat*3.1416/180)*dx) + v*dty/dy )/6.37e6
where the variable t is temperature, u is the U component of the wind, and v is the V component of the wind.

伽蓝鸟

madvw(W,EXPR)
This function calculates

   -d(W*EXPR)/dp
using an upwind scheme.

W
Vertical wind speed (w component) (unit of vertical coordinate/s, such as hPa/s for the vertical coordinate in hPa)

EXPR
An expression.

Remarks
Note that no-slip boundary conditions are assumed. i.e.,

      w(lev=0)=0
      C(lev=0)=C(lev=1)
  
      concp, wp
           |---cn
      conc, w
           |---cnm
      concm, wm