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Record 15 of 560
Wavelets, period-doubling, and time-frequency localization with application to organization of convection over the tropical western Pacific
External Online Source: doi:10.1175/1520-0469(1994)051<2523:WPDATL>2.0.CO;2
Author and Affiliation:
Weng, Hengyi(NASA Goddard Space Flight Center, Greenbelt, MD, United States)
Lau, K.-M.(NASA Goddard Space Flight Center, Greenbelt, MD, United States)
Abstract: In this paper, preliminary results in using orthogonal and continuous wavelet transform (WT) to identify period doubling and time-frequency localization in both synthetic and real data are presented. First, the Haar WT is applied to synthetic time series derived from a simple nonlinear dynamical system- a first-order quadratic difference equation. Second, the complex Morlet WT is used to study the time-frequency localization of tropical convection based on a high-resolution Japanese Geostationary Meteorological Satellite infrared (IR) radiance dataset. The Haar WT of the synthetic time series indicates the presence and distinct separation of multiple frequencies in a period-doubling sequence. The period-doubling process generates a multiplicity of intermediate frequencies, which are manifested in the nonuniformity in time with respect to the phase of oscillations in the lower frequencies. Wavelet transform also enables the detection of extremely weak signals in high-order subharmonics resulting from the period-doubling bifurcations. These signals are either undetected or considered statistically insignificant by traditional Fourier analysis. The Morlet WT of the IR radiance dataset indicates the presence of multiple timescales, which are localized in both frequency and time. There are two regimes in the variation of IR radiance, corresponding to the wet and dry periods. Multiple timescales, ranging from semidiurnal, diurnal, synoptic, to intraseasonal with embedding structures, are active in the wet regime. In particular, synoptic variability is more prominent during the wet phase of an intensive intraseasonal cycle. These are not only consistent with, but also show more details than, previous findings by using other techniques. The phase-locking relationships among the oscillations with different time-scales suggest that both synoptic and intraseasonal variations may be mixed oscillations due to the interaction of self-excited oscillations in the tropical atmosphere and external forcings such as annual and diurnal solar radiation variations. Both examples show that WT is a powerful tool for analysis of phenomena involving multiscale interactions that exhibit localization in both frequency and time. A discussion on the caveats in the use of WT in geophysical data analysis is also presented.
Publication Date: Sep 01, 1994
Document ID:
19950034718
(Acquired Dec 28, 1995)
Accession Number: 95A66317
Subject Category: METEOROLOGY AND CLIMATOLOGY
Document Type: Journal Article
Publication Information: Journal of the Atmospheric Sciences (ISSN 0022-4928); 51; 7; p. 2523-2541
Publisher Information: United States
Financial Sponsor: NASA; United States
Organization Source: NASA Goddard Space Flight Center; Greenbelt, MD, United States
NASA; Washington, DC, United States
Description: 19p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
NASA Terms: ANNUAL VARIATIONS; ATMOSPHERIC MODELS; CONVECTIVE FLOW; ORTHOGONAL FUNCTIONS; PACIFIC OCEAN; TIME SERIES ANALYSIS; TRANSFORMATIONS (MATHEMATICS); TROPICAL METEOROLOGY; WAVE PROPAGATION; CLOUD COVER; INFRARED IMAGERY; MATHEMATICAL MODELS; RADIANCE; RAIN; SATELLITE OBSERVATION
Imprint And Other Notes: Journal of the Atmospheric Sciences vol. 51, no. 7 p. 2523-2541 September 1, 1994
Miscellaneous Notes: Research sponsored by NASA
Availability Source: Other Sources
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