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Published August 2002 | Published
Journal Article Open

Cloud Halos: Numerical Simulation of Dynamical Structure and Radiative Impact


Significant enhancements in humidity around cumulus clouds, that is, the "cloud halos" observed in many aircraft penetrations, are simulated using a three-dimensional dynamic model. Five case studies show that humidity halos occur mainly near lateral cloud boundaries and also occur at cloud top and base when the cloud dissipates. The humidity halo broadens as the cloud ages and is also broader in the presence of wind shear than in its absence, especially on the downshear side of the cloud. The broadband calculation over the solar spectrum (0.2–4.0 μm) shows that the shortwave (SW) heating rate in the halo is about 11%–18% larger than the ambient environmental heating rate. The strongest halo-induced surface SW radiative forcing for all cases studied is about −0.2 W m^−2, which is approximately a 0.02% change from the forcing without a halo.

Additional Information

© 2002 American Meteorological Society Manuscript received September 14, 2001, in final form April 9, 2002 We thank Prof. Frank Evans at the University of Colorado for providing and helping with the SHDOM model. Constructive reviews from anonymous reviewers helped in the presentation of this paper. This work was supported by National Science Foundation Grant ATM-9907010.

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