| Abstract: Using a numerical model of solar radiative
transfer that is calibrated against benchmark computations, it is shown
that atmospheric water vapor, together with the microphysical characteristics
of water drops (liquid water path and effective radius), plays an important
role in the total solar spectrum reflection and absorption in overcast
skies. For any specific cloud type, the water vapor column above the cloud
and the presence of saturated water vapor inside the cloud contribute significantly
to atmospheric absorption. These factors also affect the relationship between
the net shortwave fluxes at the top and bottom of overcast atmospheres,
in particular, inhibiting a general universal linkage between these two
quantities. Thus neglect of details concerning the vertical location, extent,
and microphysical aspects of clouds can lead to biases in the inference
of surface irradiance using top-of-the-atmosphere measurements. |