RELATIONSHIP BETWEEN SOLAR NET RADIATIVE FLUXES AT THE TOP OF THE ATMOSPHERE AND AT THE SURFACE

Previous work has discussed the existence of a linear relationship bet ween the net solar radiative flux densities at the surface and at the top of the atmosphere (TOA) that can be exploited for inferring the ne t surface radiation directly from the satellite observed net radiation . In physical terms the net solar flux at the surface can be estimated from the difference between the satellite-inferred net flux at TOA an d total solar absorption in the atmosphere. This paper presents model calculations of the influence on solar absorption of water vapor, sola r zenith angle, cloud-top altitude, and cloud optical thickness. The m odel results indicate a somewhat complex relation between the solar ne t fluxes at the surface and at the top of the atmosphere. It is pointe d out that cloud altitude and optical depth have a large impact on sol ar atmospheric absorption; high clouds decrease solar absorption by th e atmosphere whereas low clouds increase it. This difference between s olar atmospheric absorption for low and high clouds increases with clo ud optical depth. An intriguing result is that changes of total atmosp heric absorption with cloud-top height are nearly completely compensat ed by corresponding changes in the net flux at the top of the atmosphe re, thus leaving the surface solar net flux constant. Furthermore, thi s paper provides a very simple parameterization for estimating the cle ar-sky solar atmospheric absorption as a function of solar zenith angl e and the vertically integrated water vapor content of the atmosphere.