Poster Session P14.4 The effects of ambient wind shear and varying initial conditions on numerically simulated mammatus-like clouds

Thursday, 30 October 2008
Madison Ballroom (Hilton DeSoto)
Katharine M. Kanak, School of Meteorology, University of Oklahoma, Norman, OK ; and J. M. Straka

Handout (2.3 MB)

Mammatus clouds have been observed to form in clusters, rows, and mixtures of these planforms, and often in association with cumulonimbus. Possible formation mechanisms for mammatus clouds are tested using numerical simulation with observed mammatus proximity soundings. In previous work, it was shown that mammatus-like clouds could be simulated in association with a cirrus anvil-type cloud using idealized three-dimensional numerical simulations. It was shown that these mammatus were sensitive to the characteristics of a sub-cloud dry layer and the ambient thermodynamic stability. In this complimentary work, the effects of ambient wind shear on the formation of mammatus are examined, as well as the effect of varying initial conditions. Results show that mammatus form, but have modified morphology, in the presence of wind shear. Mammatus do not form when wind shears exceed certain thresholds. The variation of the initial amounts of perturbation snow aggregate mixing ratios result variations in the distances mammatus may descend before all hydrometeors have sublimed. This is also dependent on the ambient thermodynamic conditions. Previous investigators have suggested that wind shear may play a role in mammatus formation. It is concluded from the numerical simulation results that wind shear is not a necessary condition for formation, but may modulate the morphology of the mammatus structures. It is also concluded that further exploration of the relationship between the initial snow aggregate mixing ratio and the ambient thermodynamic profiles is needed.
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