The interaction of a mechanically driven three-wave zonal background flow with model mountains in the Northern Hemisphere

Summary Laboratory experiments concerning the interaction of a mechanically driven, uniform shear, zonal, westerly flow superimposed on a three-wave pattern, including cut-off lows, with models of Greenland, the Rocky Mountains and Tibet are conducted. The modeling criteria considered are the matching of the Rossby, Burger and Ekman numbers as well as a number of geometrical parameters. The -effect has not been modeled.The model demonstrates the variation in strength of cut-off lows as they advect over and/or around the model mountains. For example, the low upwind of the Rocky Mountains weakens on approaching the mountains, transforming to a trough in passing over the model and then strengthening again in the lee. The model also shows the influence of the mountains in blocking the lows upstream and then having them accelerate as they advect over the topography.The experiments show how mother cut-off lows approaching the Rocky Mountains can develop daughter troughs/cut-off lows in the lee and further how these mother/daughters coalesce again in the lee. Finally the experiments demonstrate the effects of a cut-off low being advected from west to east past and to the north of the Tibetan Plateau. The process first develops a closed anticyclone in the southeastern region of the Tibetan Plateau. This anticyclone is later replaced by a trough and then a cut-off low. The experiments, generally, demonstrate a number of phenomena observed in the real atmosphere.With 12 Figures