Application of normal Morlet wavelet transform method to the damped harmonic analysis: On the isolation of the seismic normal modes (S-0(0) and S-0(5)) in time domain

Previous studies indicated that the seismic breathing normal modes S-0(0) (period similar to 20.5 min) and S-0(5) (period similar to 19.8 min) were excited by the 26th December 2004 Sumatra-Andaman earthquake. These two modes may present a beating-pattern in a wavelet time-frequency spectrum due to their close frequencies. Using superconducting gravimeter (SG) data covering 20 days after the Sumatra event, this work shows that a periodic amplitude-varying signal with an similar to 20.2 min period due to beating between the S-0(0) and S-0(5) modes is displayed in the normal Morlet wavelet transform (NMWT) spectrum, and this signal can be quantitatively extracted from the NMWT spectrum. Furthermore, the NMWT spectrum also clearly shows that this beating-pattern disappeared at time t similar to 9 x 10(3) min (when the S-0(5) mode vanished) after the Sumatra event occurred, since S-0(5) mode decays much faster than the S-0(5) mode. Using this information, we can separately isolate the S-0(0) and S-0(5) mode signals and further estimate their respective parameters (i.e., frequency-f(0), initial amplitude-A(0), and quality factor-Q) in the time domain rather than in the frequency domain only. The temporal-varying behaviour of the oSs mode in the time domain obtained in this work can be thoroughly explained by two damped harmonic signals due to the splitting of the S-0(5) mode. In brief, we can isolate S-0(0) and S-0(5) mode signals in the time-frequency domain using the NMWT method, which is different from the traditional method used in the frequency domain

Algebraic Reconstruction Algorithm of Vapor Tomography

While applying algebraic reconstruction algorithm in vapor tomography, problems have to be solved with respect to constructing the constraint condition, selecting the initial value, calculating optimal relaxation factor and deciding the iteration termination condition. Golden section search method and NCP termination rule are given to solve the latter two problems, respectively. Eight algebraic reconstruction algorithms, including Kaczmarz, Randkaczmarz, Symkaczmarz, SART, Landweber, Cimmino, CAV and DROP algorithm, are comparatively analyzed and tested by the data from SatRef station in Hong Kong. The results show that all the eight algorithms can satisfy the requirements of vapor tomography and the iteration termination condition is more important than the relaxation condition. While the golden section method and NCP method are used, the CAV algorithm performs best, and then the Cimmino algorithm

Cryospheric Excitation on the Earth's Chandler Wobble and Implications From a Warming World

Abstract Leveraging Gravity Recovery and Climate Experiment mascon products spanning from April 2002 to September 2023, we, for the first time, ascertain the substantial influence of cryospheric mass variations on Earth's Chandler wobble (CW). Further, in contrast to traditional analysis conducted in the excitation domain, this study focuses on the polar motion domain and incorporates the wavelet analysis technique. Our findings reveal some intriguing phenomena: Between 2006 and 2020, the cryosphere contributed an average amplitude of approximately 4.85 mas to CW, equivalent to 5.05%, with its impact escalating to about 11 mas from 2018 to 2022, representing a fourfold rise in its contribution ratio to approximately 20%. This marked surge can be attributed to the more erratic glacier mass balance results from ongoing climate change. Moreover, there is a pronounced decrease in the CW signal post‐2018, which starkly contrasts with cryospheric contribution, suggesting a potential linkage to climate change yet warrants further investigation