subroutine rotate_fields(itime)
      use read_file_module,only: nlon,nlat,z_mgcm,t_mgcm,u_mgcm,v_mgcm
      implicit none
!
! Args:
      integer,intent(in) :: itime
!
! Local:
      integer :: i,ii,j,nlonrot,isecs_per_day
      real :: deg_per_sec,deg_rot,deg_per_lon
      real,dimension(nlon) :: fz,ft,fu,fv
!
      deg_per_sec = 360./float(isecs_per_day)
      deg_rot = float(isecs_per_day/2)*deg_per_sec ! 1/2 day rotation
      deg_per_lon = 360./float(nlon) ! deg rotation per lon grid point
      nlonrot = nint(deg_rot/deg_per_lon)
      do j=1,nlat
        fz(:) = z_mgcm(:,j)
        ft(:) = t_mgcm(:,j)
        fu(:) = u_mgcm(:,j)
        fv(:) = v_mgcm(:,j)
        do i=1,nlon
          ii = mod(i+nlonrot-1,nlon)+1
          z_mgcm(i,j) = fz(ii) 
          t_mgcm(i,j) = ft(ii) 
          u_mgcm(i,j) = fu(ii) 
          v_mgcm(i,j) = fv(ii) 
        enddo
      enddo
      end subroutine rotate_fields