Intraseasonal oscillation in an idealized general circulation model /
The intraseasonal oscillations (ISOS) that appear in the
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1996.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=743267681&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The intraseasonal oscillations (ISOS) that appear in the perpetual equinox simulation of a spectral general circulation model (GCM) have been systematically studied. The NCAR, Community Climate Model (CCM2, R15) has been implemented on an idealized planet with no ocean and no topography and with uniform boundary conditions, such as constant vegetation and surface albedo, and also has been integrated for 15 years. The wave-frequency distributions at different latitudes, obtained from spacetime spectral analysis, show that well- defined spectral peaks occur in the eastward propagating wave components of the zonal and meridional winds, especially in the wavenumber one Component which has a period of about 40 (lays. Wavenumber 2 travels at a slightly slower phase speed and takes about 50-54 days to encircle the globe once. A phase-shifting composite procedure has been used to further demonstrate the three-dimensional spatial structure of the model's ISO. The horizontal structure of the sirtiulated oscillation is dominated by the eastward- moving wavenumber 1; wavenum- ber 2, however, is also important and its amplitude is about a half that of wavenumber 1. ISOs exhibit a baroclinic structure in the tropics but a barotropical structure in the extratropics. These results suggest that ISOs are internally generated and maintained by the model dynamics and physics. A newly-developed time-varying spectral analysis has been i-ised to study the characteristics of the temporal evolution of the intraseasonal oscillation, and thus to explore the mechanism of ISO maintenance. The most interesting and striking result is that the internally generated intra,seasona,l oscillation exhibits an episodic feature, referred to as internlittency of ISO. Large- and small- amplitilde oscillations occur intermittently. Although intermittency is a frequently observed feature in nonlinear and turbulent flows, it appears to be the first time that such interrnittency has been documented in such model studies of the intraseasonal oscillation. The relationship between the zonal-mean flow and low-frequency waves has been investigated by using the EOF analysis. The results show that intense ISOs are associated with weak, broad and poleward-shifted subtropical jets as well as intense westerlies in the upper tropics; less intense ISOs are associated with strong, narrow and equatorward- shifted subtropical jets. This finding suggests that nonlinear interactions between the zonal-mean flow and low-frequency waves may be important for maintaining the episodic feature of the intraseasonal oscillations. |
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| Item Description: | Vita. "Major Subject: Meteorology". |
| Physical Description: | xii, 94 leaves : illustrations, maps ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |