Read heat flux data, interpolate in time

INTERFACE:

    subroutine read_heat_flux(jul,secs,heat)

DESCRIPTION:

For calc_fluxes=.false., this routine reads in the sum of sensible, latent and long-wave back-radiation flux in Wm$^{-2}$ from heatflux_file and interpolate in time.

USES:

    IMPLICIT NONE

INPUT PARAMETERS:

    integer, intent(in)                 :: jul,secs

OUTPUT PARAMETERS:

    REALTYPE, intent(out)               :: heat

REVISION HISTORY:

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