Date of Award
Doctor of Philosophy
Physics and Astronomy
John L. Stanford
A method proposed by Salby (1982a,b) for computing the zonal spacetime Fourier transform of asynoptically acquired soundings from polar-orbiting satellites has been implemented, tested, and applied in two investigations of atmospheric motions;It is demonstrated that the technique is robust under real data conditions, providing meaningful results in the presence of randomly varying signals, sampling errors, and missing data. The spectra computed display several advantageous characteristics: a frequency range which includes very short periods, a lack of distortion due to the asynoptic nature of the data, and (for instruments with multiple scan tracks) a high degree of statistical reliability which is obtained by averaging over closely-spaced spectra. The method is thus well suited for detecting features with small amplitudes and/or short periods;The method is applied to measurements of brightness temperature from the Southern Hemisphere polar winter. In accordance with the results of Prata (1984), a series of waves is seen which have wave-numbers 1 to 3 and travel with the same phase speed. In addition, a wave 4 traveling oscillation, is seen. Synoptic reconstructions of the fields are used to show that the sequence of waves constitute a series of warm pools circling the pole with a period of about 3.6 to 3.8 days. These warm pools are observed to have extraordinarily long lifetimes (at least one month), and on several occasions may be seen to collide and coalesce;Finally, the method is applied to a search for two fast-moving waves predicted in a numerical model. The ability of the method to detect very small signals is used to demonstrate the nonexistence of the modes during the time period analyzed;References. Prata, A. J., 1984: The 4-day wave. J. Atmos. Sci., 41, 150-155. Salby, M. L., 1982a: Sampling theory for asynoptic satellite observations. Part I: Space-time spectra, resolution, and aliasing. J. Atmos. Sci., 39, 2577-2600. Salby, M. L., 1982b: Sampling theory for asynoptic satellite observations. Part II: Fast Fourier synoptic mapping. J. Atmos. Sci., 39, 2601-2614.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Leslie Robert Lait
Lait, Leslie Robert, "Space-time spectral studies of global stratospheric temperature fields " (1987). Retrospective Theses and Dissertations. 8669.