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Gravitational waves (GWs) from core-collapse supernovae (CCSNe) have been proposed as a probe to investigate the physical properties inside supernovae. However, how to search for and extract the GW signals from CCSNe remains an open question owing to their complicated time–frequency structure. In this paper, we apply the ensemble empirical mode decomposition (EEMD) method to decompose and reconstruct simulated GW data generated by the magnetorotational mechanism and the neutrino-driven mechanism within the Advanced LIGO, using the match score as the criterion for assessing the quality of the reconstruction. The results indicate that by decomposing the data, the sum of the first six intrinsic mode functions (IMFs) can be used as the reconstructed waveform. To determine the probability that our reconstructed waveform corresponds to a real GW waveform, we calculate the false alarm probability of reconstruction (FAPR). By setting the threshold of the match score to be 0.75, we obtain the FAPRs of GW sources at distances of 5 and 10 kpc to be 6 × 10−3 and 1 × 10−2, respectively. If we normalize the maximum amplitude of the GW signal to 5 × 10−21, the FAPR at this threshold is 4 × 10−3. Furthermore, in our study, the reconstruction distance is not equivalent to the detection distance. When the strain of GWs reaches 7 × 10−21, and the match score threshold is set at 0.75, we can reconstruct GW waveforms up to approximately 36 kpc. [ABSTRACT FROM AUTHOR]

An analytically based method is proposed to simulate the acoustic-gravity waves in the horizontally stratified atmosphere-Earth structure generated by a point force on the Earth's surface. The method solves the linear momentum, continuity and adiabaticity equations in the atmosphere and elastodynamic equations in the solid Earth in the frequency–wavenumber domain. The time-domain waveforms are obtained by wavenumber integration and fast Fourier transform with respect to the frequency. Numerical simulations are conducted to investigate the properties of the acoustic-gravity waves, including both the high-frequency acoustic-mode waves and low-frequency gravity-mode waves. Simulations of the high-frequency responses show that disturbances in the atmosphere with three apparent horizontal velocities can be identified. They are, namely, the direct acoustic-mode wave generated by source travelling with the sound speed, the head wave generated by the seismic P -wave travelling with apparent horizontal speed identical to the P velocity, and the head wave generated by the Rayleigh wave with a horizontal speed same to the Rayleigh wave velocity. Simulations of the low-frequency responses show that the gravity-mode wave and Lamb wave can be identified. The gravity-mode wave travels with a speed lower than the sound seed and does not reach everywhere, especially the area directly above the source. The Lamb wave travels along the Earth surface with a speed of about 310 m s–1 and its energy decays with the altitude. We also apply our method to explaining the Doppler sounding data observed in Taiwan area during the 2011 Tohoku M 9 earthquake, and find good agreement between the predicted signals and observed data in the arrival time and wave envelope associated with the Rayleigh wave. [ABSTRACT FROM AUTHOR]

It was known that the Solar quiet (Sq) current is important for the ionosphere dynamics, which can cause variations in the geomagnetic fields recorded on the ground. Using a north‐south chain of observatories, the latitude of the Sq focus (center of the solar quiet current) can be determined in a local area. However, a single chain of observatories does not provide the longitudinal information of the Sq focus. In this study, we proposed an improved method using a magnetic observatory network in Asia to determine the focus automatically. After taking the variability and asymmetry of the Sq current into consideration, the proposed method determines the Sq focus with the longitudinal and latitudinal fitting processes. To verify the effectiveness of this method, we designed an observing procedure experiment (OPE) to simulate the geomagnetic field observation and focus determination under different conditions. The results show that the proposed method has the capability of tracking the trajectory of the Sq focus. Additionally, the OPE can efficiently validate the performance of the method. Plain Language Summary: An electric current named Solar quiet (Sq) current exists in the atmosphere at an altitude of near 100 km. The Sq current is a vortex electric current that moves westward around the Earth with the apparent move of the Sun. The center of the vortex is the focus, which is similar to the eye of a cyclone. The Sq current can change the geomagnetic field recorded on the ground. We can deduce the current in the upper atmosphere base on the geomagnetic variations near the ground. In this study, we proposed a method to automatically determine the position of the focus at a given time. This method enables us to get the ground track of the Sq current. We further designed an observing procedure experiment to evaluate different methods for determining the focus. The results show that the improved method has high accuracy on both longitude and latitude. Key Points: Two‐step method with the observing procedure experiment (OPE) determines and validates the Solar quiet (Sq) focus positionUtilizing the geomagnetic observatory network and the two‐step method to obtain the movement of the Sq focusThe OPE to estimate the distribution, total number, and density of observatories required for the method [ABSTRACT FROM AUTHOR]