11th Conference on Atmospheric Radiation and the 11th Conference on Cloud Physics

Monday, 3 June 2002
Capacitance of bullet rosette ice crystals
Mihai Chiruta, Univ. of Wisconsin, Madison, WI; and P. K. Wang
Poster PDF (303.3 kB)
It has recently become clear that cirrus clouds significantly affect the global energy balance and climate, due to their great radiative impact on atmospheric thermal structure. In order to assess the impact of cirrus clouds on global climate, numerical models of cirrus are constructed to investigate how ice crystals in cirrus interact with solar and terrestrial radiations.

The radiative properties of cirrus are sensitive to ice concentration and size distribution, which, in turn, are related to the ice growth rate. In cirrus models, the ice growth rates are usually parameterized using the electrostatic analog theory and the crucial quantity is the capacitance. So for an accurate assessment of cirrus on climate, we need to have accurate information about the capacitances of ice crystal habits that occur frequently in cirrus clouds.

One of the most common ice habits in cirrus is bullet rosette. Yet there is no information of the rosette capacitance available from either experimental measurements or theoretical calculations. This paper will report on the numerical calculations of the capacitance of bullet rosettes based on the explicit solutions of the Laplace equation. Seven bullet rosettes are considered here V rosette with 2, 3, 4, 6, 8, 12, 16 lobes. The surfaces of the rosettes are approximated by simple mathematical expressions. The Laplace equation with proper boundary conditions is solved numerically by finite element techniques. The results show that the rosette capacitances are substantially different from that of spheres of equal radius.

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