Read momentum flux data, interpolate in time

INTERFACE:

    subroutine read_momentum_flux(jul,secs,tx,ty)

DESCRIPTION:

For calc_fluxes=.false., this routine reads momentum fluxes in Nm$^{-2}$ from
momentumflux_file and interpolates them in time.

USES:

    IMPLICIT NONE

INPUT PARAMETERS:

    integer,intent(in)                  :: jul,secs

OUTPUT PARAMETERS:

    REALTYPE,intent(out)                :: tx,ty

REVISION HISTORY:

    Original author(s): Karsten Bolding
    See log for airsea module

LOCAL VARIABLES:

    integer                   :: yy,mm,dd,hh,min,ss
    REALTYPE                  :: t,alpha
    REALTYPE, save            :: dt
    integer, save             :: mom_jul1,mom_secs1
    integer, save             :: mom_jul2,mom_secs2
    REALTYPE, save            :: obs1(2),obs2(2)
    integer                   :: rc