Characteristics of 1-2 week cyclic behavior of subtropical wind maxima over the Australian-South Pacific region
Abstract
Statistical methods and a compositing technique are applied to examine subtropical zonal wind maxima at 200 hPa over the Australian-South Pacific region. Five consecutive 6-month (November-April) periods of zonal wind data are analyzed for the years 1984-85 to 1988-89. A pilot study for the period, November 1984-April 1985, was conducted and jets were found to develop over eastern Australia and take about 10 days to propagate across the western Pacific before dissipating or moving toward higher latitudes. This behavior showed a cyclic pattern with a period of about 1-2 weeks. The vertically-integrated mean and shear kinetic energies suggested that baroclinic processes dominate in the entrance and core regions of the propagating jets, whereas barotropic processes dominate in the exit and downstream regions. Results from the 1985-89 period, which contained an ENSO cycle, revealed similar features to the pilot study. During the 1986-87 El Nino, the whole jet pattern moved eastward about 15-20 degrees longitude, and the jet maxima were greater than in the other years. The application of lag correlations between the jet and 200 hPa geopotential height supported the quasi-periodic behavior and suggested that mid-latitude trough/ridge systems helped propagate the subtropical jet streaks eastward. The importance of the divergent circulations in supporting the rotational flow was demonstrated by an analysis of the partitioned kinetic energy budget. The rotational horizontal flux term showed that energy was transported from the entrance to the exit region of the jet, suggesting that self-advection was a major mechanism behind the 1-2 week behavior of the South Pacific jets. Maximum conversion of divergent to rotational flow occurred in the trailing edge of the jets, and this conversion and the divergent generation were in good agreement, indicating that most of the generated divergent kinetic energy occurred in the entrance regions.
Degree
Ph.D.
Advisors
Vincent, Purdue University.
Subject Area
Atmosphere
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