J1.6
Rossby-wave/orographic dynamics of the northern hemisphere
Peter B. Rhines, Univ. of Washington, Seattle, WA
The cyclonic activity of the mean Arctic sea-level pressure and its oceanic image develops through advective penetration from the Atlantic region (in high-NAO winters). This opposes the anticyclonic tendency of the Beaufort gyre and its atmospheric image, which has origins in both diabatic cooling and pv-stirring excited from the south. A simple model of Greenland's orography presents a ‘pv-bridge' to facilitate this Arctic penetration, and actively stimulates lee cyclogenesis and intense tip-jets at its southern extremity, A ‘Lighthill' mode of upwind Rossby/orographic blocking has great impact. This mode is seen in a rotating fluid experiment using optical altimetry which images the surface height field (www.ocean.washington.edu/research/gfd/gfd.html), first figure. This is a polar beta plane experiment in a single-layer fluid, viewed from above the North Pole. A mountain at 3 o'clock blocks the solid-body westerly flow, with a blocking plume (light shade) propagating westward round a latitude circle. The second image shows the formation of a lee jet south of the mountain, and short lee Rossby waves farther east. Above the mountain, topographic Rossby waves wind a spiral height-field with strong gradient corresponding to large velocities. Meanwhile the oceanic inflow from Atlantic to Arctic, beneath these wind and buoyancy flux fields, is sensitive to both local- and also more distant atmospheric forcing. Heat and fresh-water transport of these ocean and atmosphere systems is channeled in the Atlantic sector, and is an important element of global climate. Illustrations use shallow water lab- and numerical simulations. Vertical structure and synoptic development of these events may also be discussed.
Joint Session 1, dynamics and Changes of climate modes, including annular modes (Joint with Middle Atmosphere, Fluid Dynamics and Climate Variations)
Monday, 13 June 2005, 10:30 AM-6:15 PM, Ballroom D
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