Dynamics of the nonmigrating semidiurnal tide in the mesosphere and lower thermosphere over the Antarctic and Arctic [microform]
- Bib ID:
- 4740314
- Format:
- Book and Microform
- Author:
- Hiroyuki, IImura
- Online Version:
- http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3337103
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- Description:
- 247 p.
- ISBN:
- 9780549917175
- Summary:
-
This dissertation focuses on the structure of the nonmigrating semidiurnal tide in the high latitude Mesosphere and Lower Thermosphere (MLT). Comparing the spatial structure and seasonal variation of the nonmigrating semidiurnal tide in the high latitude MLT will help to improve our understandings of forcing mechanisms of the atmospheric tides. In this study, the horizontal wind velocities measured by the TIMED Doppler Interferometer (TIDI) on the Thermosphere - Ionosphere - Mesosphere Energetics and Dynamics (TIMED) mission are analyzed. TIDI observes the wind field from pole to pole every orbit, and therefore, provides an opportunity to determine the seasonal variation of each nonmigrating semidiurnal tidal component at high latitudes, where few observations exist. There are three major semidiurnal tidal components observed clearly at high latitudes. These are westward-propagating with zonal wavenumbers 1 (W1) and 3 (W3) and a standing oscillation with the zonal wavenumber 0 (S0).
The W1 component dominates the nonmigrating semidiurnal tidal wind field in the vicinity of the poles during summer. However, the amplitude of this component is much greater in the vicinity of the South Pole than in the vicinity of the North Pole. Additionally, the enhancement of this component in the vicinity of the South Pole persists for a longer period of time and at a lower altitude. Additionally, the amplitude and phase of the W1 component exhibit significant latitudinal gradients in the Antarctic. The vertical wavelength of the W1 component has a significant latitude variation during mid-summer, with a shorter vertical wavelength being observed as one approaches the pole in both hemispheres. While the overall structure of the S0 component is similar to the W1 component, the S0 component decays in amplitude as the pole is approached. The structure of the W3 component is different from the W1 and S0 components.
This component appears when and where the W1 and S0 components are weak. Over all, the nonmigrating semidiurnal tides are greater over the Antarctic than the Arctic. The correlation of the W1 nonmigrating semidiurnal tide with the zonal wavenumber 1 stationary planetary wave (SPW1) is examined. Amplitudes of the SPW1 have been computed using temperature measured from the Sounding of the Atmospheric using Broadband Emission Radiometry (SABER) instrument on TIMED. When the W1 component is enhanced in one hemisphere the SPW1 is enhanced in the opposite hemisphere. Additionally, the enhancement in the SPW1 is greater in the winter northern hemisphere than in the winter southern hemisphere. This result supports the nonlinear interaction theory for the W1 component in the summer high latitudes by the SPW1 in the winter hemispheres. However, inter-annual correlations between the W1 component and the SPW1 are not consistent with the inter-hemispheric correlations.
Therefore, it is possible that there are additional forcing mechanisms or mitigating factors in the excitation of the W1 component. Finally, the W1 component in the temperature field at low and middle latitudes and in the wind field at high latitudes were examined by using a Hough function decomposition. The W1 component in the high latitude wind field predicted from the component in the temperature field has significant structural difference. These results indicate that the W1 component at high latitudes is influenced by forcing mechanisms which are not included in the classical tidal theory.
- Notes:
-
- (UMI)AAI3337103
- Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6642.
- Adviser: Scott E. Palo.
- Thesis (Ph.D.)--University of Colorado at Boulder, 2008.
- Reproduction:
- Microfiche. Ann Arbor, Mich. : University Microfilms International.
- Subject:
- Atmospheric Sciences
- Other authors/contributors:
- University of Colorado at Boulder. Aerospace Engineering
- Copyright:
-
In Copyright
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Copyright status was determined using the following information:
- Material type:
- Literary Dramatic Musical
- Published status:
- Unpublished
- Creation date:
- 2008
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