The Dynamics of Teleconnections Induced by Short Term Tropical Forcing.

• Main Author: Malsick, Mark D.
• Other Authors: NAVAL POSTGRADUATE SCHOOL MONTEREY CA
• Format: Text
• Language: English
• Published: 1995
• Subjects: Meteorology; Computer Programming and Software; *COMPUTERIZED SIMULATION; *WEATHER FORECASTING; *PERTURBATIONS; *TROPICAL CYCLONES; MATHEMATICAL MODELS; ANOMALIES; TRANSIENTS; GROWTH(GENERAL); COHERENCE; VORTICES; REGIONS; SHALLOW WATER; RESPONSE; PATTERNS; TROPICAL REGIONS; NORTH ATLANTIC OCEAN; EXITS; WAVES; NORTH PACIFIC OCEAN; INDUCTION SYSTEMS; GRADIENTS; NORTH AMERICA; OCEAN BASINS; BENGAL BAY; ROSSBY WAVES; *TELECONNECTIONS; WESTERN NORTH PACIFIC OCEAN; Pacific; North Atlantic
• Online Access: http://www.dtic.mil/docs/citations/ADA305941; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA305941

Recent observational and modeling studies have suggested that transient tropical perturbations may induce significant intraseasonal teleconnections between the tropics and midlatitudes. We have investigated the mechanisms for such teleconnections using a nonlinear global shallow water model with a realistically wavy basic state. The model perturbations were designed to simulate tropical cyclones with prescribed growth, decay, and propagation. The model responses to the tropical perturbations showed distinct midlatitude wavetrain responses to the perturbation. The typical response became large within a few days and retained as a coherent pattern for two to three weeks after the demise of the tropical perturbation. The response was particularly strong if the perturbation propagated close to an extratropical jet. This propagation allowed Rossby wave induction as divergent outflow from the perturbation crossed the jet's region of high ambient vorticity gradient. This initial wave response was then guided by the jet and amplified in barotropically unstable regions on the jet flanks. This produced a persistent response downstream of the jet exit (e.g., over the northeast Pacific and North America). The response showed a marked variation with the season and with the tropical ocean basin in which the perturbation occurred, apparently because of temporal and spatial changes in the basic state conditions. The responses closely resemble observed anomaly patterns associated with transient tropical perturbations, and are dynamically consistent with the responses to more persistent tropical perturbations (e.g., ENSO events).