Ramaswamy, V., and A. Detwiler, 1986: Interdependence of radiation and microphysics in cirrus clouds. Journal of the Atmospheric Sciences, 43 (21), 2289-2301.
Abstract: The important microphysical relationships determining the radiative properties
and growth of ice crystals in stratiform cirrus clouds are investigated.
A horizontally infinite cloud layer is modeled in the midlatitude upper
troposphere. Optical properties of spheres of equal surface area are assumed
to represent the scattering characteristics of nonspherical crystals, while
the delta-Eddington approximation is used to solve the radiative transfer
equations.
Classical expressions for ice particle growth and sublimation are coupled
to those for radiative energy exchange in order to follow ice particle evolution
within the cloud. The radiative properties of the clouds influence the balance
among the cloud physical processes within the cloud. In the top 5 percent
of optically thin clouds, the ice particle energy balance is essentially
between latent and heat diffusion. In the case of clouds with large optical
depths, the energy balance is between latent heat and radiation, i.e., radiative
cooling enhances particle growth by vapor deposition. In the lower 5 percent
of optically thin or thick clouds, latent heat and radiation are balanced
by the diffusion of heat from the particle to the environment. Here, upwelling
radiation enhances particle sublimation at cloud base. Environmental ice
saturation ratio is the primary factor determining the energy balance during
growth of ice crystals. When the ice saturation ratio is ~ 1, crystal growth
rates are small, and radiative heating/cooling exercises a strong influence.
However, for ice saturation ratios more than a percentage above or below
unity, radiative influences on growth rates of crystals with lengths less
than 200 um are negligible.
We have followed the one-dimensional temporal evolution of 1-km thick cirrus
cloud layers subsiding in still air. Crystals at cloud top grow larger with
time while those at cloud base sublimate as the cloud settles into dry air,
with the vertical fall distance greater for larger initial crystal lengths.
The temporal evolution of the cloud microphysical characteristics results
in modification of the radiation fields, both within the cloud and at the
cloud boundaries.