Rossby-wave/orographic dynamics of the northern hemisphere

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.