Research Project: Optical property calculations and radiation parameterizations in support of CERES Science Team
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Ice clouds and snow on the surface play a major role in the Earth–atmosphere energy budget through
their interactions with shortwave and longwave radiation. The single-?scattering properties of ice
crystals are fundamental to radiative transfer simulations and remote sensing implementations
concerning the microphysical and optical properties ice clouds and snow. Generally speaking, ice
crystals in clouds and particles in snow on the surface are almost exclusively nonspherical
particles with the single-?scattering properties deviating substantially from the counterparts
based on the “equivalent” ice spheres. Therefore, it is necessary to use appropriate optical
properties of ice crystals and snow particles.
In support of the CERES (Clouds and the Earth’s Radiant Energy System) Science Team, our research
group at Texas A&M University has developed a two-?habit model (THM) for ice cloud optical
properties. Figure 1 shows the ice particle shape distribution assumed for the THM. The optical
properties associated with the THM leads to improvements in downstream applications to satellite
remote sensing. For example, Figure 2 shows the polarized reflectivities simulated based on the
CERES Edition 2 and the THM optical properties in comparison with the observations made by the
Polarization and Directionality of the Earth’s Reflectance (POLDER). Overall, the observed
polarized reflectivity decreases with increasing scattering angle over a range of 100°–170°. The
simulations based on the THM closely match with those from the observations except at the
scattering angles with 100–120° because of the weak polarized side-?scattering by the THM, whereas
the simulations based on the CERES Edition 2 substantially deviate from the observations. It is
obvious that THM represents a significant improvement compared the CERES Edition 2 ice cloud
optical model.
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