Extended Abstract (544K)P1.14
Nonlinear scale interactions in lake-effect clouds
Natasha L. Miles, Penn State University, University Park, PA; and J. Verlinde
Horizontal roll vortices ocassionally occur in atmospheric conditions in which theory predicts only cellular organization. One possible contributor to the occurrence of rolls in such conditions is nonlinear interactions between different scales of motion. A major objective of the Lake-Induced Convection Experiment (Lake-ICE) was to investigate these nonlinear interactions.
During Lake-ICE, transient linear organization was observed during a wintertime lake-effect event, characterized by large positive buoyancy flux and moderate wind shear. The primary dataset discussed in this paper is a time series of vertical velocity obtained with a 94-GHz cloud radar sensitive to cloud droplets and ice crystals. The cloud radar, deployed on the downwind shore of southern Lake Michigan, was used to measure high temporal resolution vertical velocity data at several in-cloud heights. The duration of the measurements was eighteen hours, encompassing three cycles of linear organization switching to cellular organization indicated by wavelet analysis. Predictors of linear organization suggested in the current literature--stability parameter, surface buoyancy flux, and shear--were not found to drive the organizational mode switching. Temporal changes in latent heat release did, however, affect nonlinear interactions between roll-scale and turbulence-scale vertical velocity. Composites of these nonlinear interaction terms in the roll-scale vertical turbulent kinetic energy budget revealed that upscale transfer from turbulence scales tended to strengthen the rolls. Although nonlinear interactions can not alone cause linear organization, the associated upscale energy transfer contributed to transient linear organization in atmospheric conditions not favorable for rolls.
Poster Session 1, Cloudy and Convective BLs
Monday, 15 July 2002, 2:00 PM-2:00 PM
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