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Cloud-resolving simulations of tropical cirrus clouds




Mitrescu, Cristian, author

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Since up to 20% of the Tropics is covered by cirrus clouds, it is expected that they strongly influence the atmospheric radiative balance and the thermal equilibrium of the Earth through their complex microphysical structure. Two-dimensional and three-dimensional simulations of a cirrus cloud event over the Western Pacific during TOGA COARE were performed using RAMS in an LES configuration. Both simulations showed the formation of two layers separated by a dry layer. In the top layer pristine ice was the dominant feature while in the bottom one mostly aggregates were present. The two layers proved to be coupled in the presence of internal stratification. Mixing ratios for the hydrometeors (only pristine ice, snow, aggregates and cloud droplets were allowed) and the vertical profiles are consistent with measurements. Within these two layers a layered structure and a horizontal variability is observed. Like other studies and measurements it is showed that the nature of turbulence in cirrus clouds is two-dimensional and buoyancy is the main source. Heating rates, which are responsible for inducing convection that is important in the maintenance of cirrus clouds, computed with the new radiation scheme, are about -17 K/day which is consistent with other models. Since one of the goals of the TOGA COARE is to determine new parameterizations that can be used in single-column models, the Probability Distribution Function for vertical velocity was computed and approximated with a Gaussian function. This can be latter used when computing various terms that depend on speed in the microphysical module.


April 30, 1998.
Also issued as author's thesis (M.S.) -- Colorado State University, 1998.

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Cirrus clouds
Clouds -- Tropics
Clouds -- Dynamics


Associated Publications