8.3 Kelvin-Helmholtz waves within gravity-wave induced lenticular clouds

Wednesday, 30 June 2010: 12:00 AM
Cascade Ballroom (DoubleTree by Hilton Portland)
Brad A. Baker, SPEC Incorporated, Boulder, CO; and P. Lawson and I. Blade

Observations of wave clouds often reveal considerable structure embedded within gravity waves. Occasionally such structure is nearly periodic, i.e., wave-like, but on length scales shorter than expected for gravity waves; at other times it can appear quite random. We use examples from the ICE-L data-set to suggest that Kelvin-Helmholtz waves are a likely explanation for much of the observed additional structure.

Dry and moist Kelvin-Helmholtz instabilities are defined that are analogous to dry and moist convective instabilities. For dry conditions, wind sheer (potential temperature lapse rate) may build up only until the dry threshold for K-H waves (convection) is reached. At that point the mixing that ensues quickly limits further build up. Regions of the atmosphere may remain stable to dry conditions for long periods while still being quite unstable to moist conditions, until condensation occurs, at which point significant instability is released in the form of K-H waves (convective cloud). This may explain why additional wave-like structure can be relatively common within certain gravity-wave induced lenticular clouds.

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