Tamara Singleton-Goyea, PhD Candidate

Graduate Research

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Role of Gravity Waves in Determining Cirrus Cloud Properties
Tamara Singleton, Dr. David O'Starr and Dr. Ruei-Fong Lin

Cirrus clouds are important in the Earth's radiation budget. They typically exhibit variable physical properties within a given cloud system and from system to system. Ambient vertical motion is a key factor in determining the cloud properties in most cases. The obvious exception is convectively generated cirrus (anvils), but even in this case, the subsequent cloud evolution is strongly influenced by the ambient vertical motion field. It is well know that gravity waves are ubiquitous in the atmosphere and occur over a wide range of scales and amplitudes. Moreover, researchers have found that inclusion of statistical account of gravity wave effects can markedly improve the realism of simulations of persisting large-scale cirrus cloud features.Here, we use a 1-dimensional (z) cirrus cloud model, to systematically examine the effects of gravity waves on cirrus cloud properties. The model includes a detailed representation of cloud microphysical processes(bin microphysics and aerosols) and is run at relatively fine vertical resolution so as to adequately resolve nucleation events, and over an extended time span so as to incorportate the passage of multiple gravity waves. The prescribed gravity waves "propagate" at 15 m s-1, with wavelengths from 5 to 100 km, amplitudes range up to 1 m s-1. Despite the fact that the net gravity wave vertical motion forcing is zero,it will be shown that the bulk cloud properties, e.g., vertically-integrated ice water path, can differ quite significantly from simulations without gravity waves and that the effects do depend on the wave characteristics.

References

Demoz, B., Starr, D., Chan, K., and S. Bowen (1998): Wavelet analysis of dynamical processes in cirrus, Geophysical Research Letters , 29, 1347-1350.

Lynch, D., Starr, D., and G. Stephens, Cirrus, Oxford University Press, 2002.

Lin, R.F. (1997): A numerical study of the evolution of nocturnal cirrus by a two-dimensional model with explicit microphysics. Ph.D. Dissertation. The Pennsylvania State University, University Park, August 1997.

Lin, R.F., Starr, D., Reichardt, J., and P. DeMott (2005): Nucleation in synoptically forced cirrostratus, J. Atmos Res.,,110(D08208),doi:10.1029/2004JD005362.

Starr, D., Singleton, T., and R.F. Lin (2008): Role of gravity waves in determining cirrus cloud properties. International Conference on Clouds and Precipitation Cancun, Mexico 5-12 July 2008.International Conference on Clouds and Precipitation Poster