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Instantaneous phase shift of annual subsurface temperature cycles derived by the Hilbert‐Huang transform
Author(s) -
Sun YangYi,
Chen ChiehHung,
Liu JannYenq,
Wang ChungHo,
Chen DengLung
Publication year - 2015
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2014jd022574
Subject(s) - precipitation , hilbert transform , thermal diffusivity , climatology , hilbert–huang transform , phase (matter) , oscillation (cell signaling) , thermal , environmental science , intensity (physics) , atmospheric sciences , geology , meteorology , thermodynamics , mathematics , physics , chemistry , spectral density , white noise , quantum mechanics , biochemistry , statistics
This study uses the Hilbert‐Huang transform to compute the instantaneous (daily) phase shift between temperature signals at the ground surface and at a depth of 5 m. This approach is not restricted to the stationary harmonic surface temperature assumptions invoked by analytical solutions. The annual cycles are extracted from the ground surface temperatures and the shallow subsurface temperatures at 5 m depth recorded at the Hualien (23.98°N, 121.61°E) and Ilan (24.77°N, 121.75°E) meteorology stations of Central Weather Bureau in Taiwan from 1952 to 2008. Significant reductions in the phase shift and increases in the estimated thermal diffusivity from 1980s to 1990s are found and suggest that the recent warming of the Pacific Decadal Oscillation may affect heat transport in the subsurface environment. The marginal spectra of the instantaneous phase shifts and the precipitation intensity records at Hualien and Ilan reveal that precipitation may play a role in the evolution of seasonal variation in shallow subsurface heat transport.