c
c------------------------------------------------------------------
c Begin file /home/sting/foster/gonz/mkuvmag.f
c------------------------------------------------------------------
c
      subroutine mkuvmag(rlat,rlon,alt,un,vn,unmag,vnmag,spval)
c
c Find neutral wind in magnetic coords
c
c On input:
c   rlat,rlon = geographic lat,lon grid point
c   alt = desired altitude (passed to igrf)
c   un,vn = neutral zonal and meridional wind at geog lat,lon
c On output:
c   unmag,vnmag are defined
c
      parameter(pi=3.14159, dtr=pi/180.)
      data yeargrf /1985./
c     
c Use igrf model (from library /FOSTER/lib/igrf.a) to find geomagnetic
c coords and declination and inclination (see sting dir ~/igrf/ymp):
c
      call igrf(rlat,rlon,alt,yeargrf,gmaglat,gmaglon,dinc,decl)
      decr = decl*dtr
      cosd = cos(decr)
      sind = sin(decr)
      if (un.ne.spval.and.vn.ne.spval) then
        unmag = un*cosd - vn*sind
        vnmag = un*sind + vn*cosd
      else
        unmag = spval
        vnmag = spval
      endif
c
      return
      end