| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2001: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2000: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1999: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
This project investigated formation dynamics of some of the large-scale atmospheric anomaly patterns that dominate over the seasonal and longer time scales. In addition to identifying modal patterns with observational data and integrations of simplified quasi-geostrophic and atmospheric general circulation models, linear dynamical models have been constructed and used in a variety of manners in order to obtain stationary large-scale responses and their modal decompositions and to evaluate feedback effects of ensemble of transient weather disturbances onto larger-scale flows.
With regard to so-called Arctic, or North-Atlantic, Oscillation (AO/NAO) pattern, it is demonstrated that it can be identified as a least-damped singular mode of a linear operator for small amplitude deviations from the wintertime climatological mean state. Its dynamics, or the mechanism for the near neutrality, can be understood by a constructive interference between zonal flow anomalies and planetary-scale zonally
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asymmetric components through eddy momentum fluxes. This feedback is more effective over the North Atlantic where the climatological eddies have smaller longitudinal scales in comparison with the Pacific counterpart, explaining the dominance of the NAO signal in the so-called AO pattern.
Furthermore, through the analysis of the linear operator, existence of a new, zonally-symmetric mode in the tropics has been unveiled, and the mode has been named a tropical Axisymmetric Mode (TAM). Investigating observational data and long-term general circulation model integrations, it is found that the mode indeed is statistically as well as physically significant and plays an important role in forming an upstream ENSO teleconnection over the Asian continent.
It is well-known that the summertime subtropical anticyclone over the ocean to the south of Japan has a large interannual variability and affects seriously the East Asian climate to its north. Through an analysis of the 1998 summer case, the season when severe flood events dominated over the East Asian countries, it is found that an anomalous intensification of the western Pacific anticyclone was induced remotely through divergent circulations associated with positive sea surface temperature anomalies both over far eastern equatorial Pacific, off the coast of Peru, and over the South Indian Ocean off Sumatra. Strong descendent flow anomalies over the sea to the east of Philippines suppressed in-situ convective activity and locally induced the anticyclonic anomaly in the lower troposphere. Southwesterly anomaly associated with the intensified anticyclone brought moist air to the East Asian countries and contributed to the anomalous wet summer. An atmospheric general circulation model experiment with climatological mean sea surface temperatures indicate that the western Pacific subtropical anticyclone is an intrinsic mode of moist atmospheric dynamics under the climatological basic state. Exploration of its formation dynamics and of effective forcing mechanisms by, e.g., local and remote sea surface temperature anomalies is an important future subject. Less
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