Detection of Climatic Fluctuations by Hilbert-Huang Method in the Data of Zagreb–Grič Observatory

Petrov, Ana (2016) Detection of Climatic Fluctuations by Hilbert-Huang Method in the Data of Zagreb–Grič Observatory. Diploma thesis, Faculty of Science > Department of Geophysics.

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Abstract

Hilbert-Huang transform (HHT), consisting of empirical mode decomposition (EMD) and Hilbert spectral analysis (HSA), is an empirically based data-analysis method which can be used to extract the periodic components embedded within nonlinear and nonstationary data. The empirical mode decomposition, the method that decomposes the original series into so called intrinsic mode functions (IMF), is applied to the series of annual and seasonal averages of temperature, cloudiness, air pressure and annual and seasonal sums of precipitation observed in Zagreb-Gric, in the period 1862.–2015. The analysis of low frequency IMFs has shown significant influence of the North-Atlantic oscillation on the temperature, cloudiness and precipitation series, both annual and seasonal. For these same elements, the analysis revealed mild deviations in natural fluctuations of the signal in the last 30 years, which are most likely caused by antropogenic activities. Next, Hilbert transform is applied to each IMF obtained for the series of annual averages of air pressure. In order to validate this approach and the results, associated Hilbert spectrum is compared with the wavelet analysis. Comparison showed significantly improved time and frequency resolution of HHT. Moreover, HHT showed unique capability of displaying intrawave frequency modulation (IFM), i.e. changes in frequency that occur within one cycle of oscillation.

Item Type: Thesis (Diploma thesis)
Keywords: Hilbert-Huang transform, Wavelet transform, North Atlantic Oscillation, NAO
Supervisor: Grisogono, Branko
Date: June 2016
Subjects: NATURAL SCIENCES > Geophysics > Meteorology and Climatology
Divisions: Faculty of Science > Department of Geophysics
Depositing User: Iva Vrkic
Date Deposited: 20 Jun 2016 09:17
Last Modified: 20 Jun 2016 09:57
URI: http://digre.pmf.unizg.hr/id/eprint/4887

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