Tsunami Waves and Tsunami‐Induced Natural Oscillations Determined by HF Radar in Ise Bay, Japan

Abstract

Tsunami waves and the subsequent natural oscillations generated by the 2011 Tohoku earthquake were observed by two high‐frequency (HF) radars and four tidal gauge records in Ise Bay. The radial velocity components of both records increased abruptly at approximately 17:00 (JST) and continued for more than 24 h. This indicated that natural oscillations followed the tsunami in Ise Bay. The spectral analyses showed that the tsunami wave arrivals had periods of 16–19, 30–40, 60–90, and 120–140 min. The three longest periods were remarkably amplified. Time‐frequency analysis also showed the energy increase and duration of these periods. We used an Empirical Orthogonal Function (EOF) to analyze the total velocity of the currents to find the underlying oscillation patterns in the three longest periods. To verify the physical properties of the EOF analysis results, we calculated the oscillation modes in Ise Bay using a numerical model proposed by Loomis. The results of EOF analysis showed that the oscillation modes of 120–140 and 60–90 min period bands were distributed widely, whereas the oscillation mode of the 30–40 min period band was distributed locally. The EOF spatial patterns of each period showed good agreement with the eigenmodes calculated by the method of Loomis (1975). Thus, the HF radars were capable of observing the tsunami arrival and the subsequent oscillations.

Quantitative Assessment of Sea Surface Salinity Estimates Using a High-Frequency Radar in Ise Bay, Japan

“…Here, we expressed this as a linear function approximation that represents the attenuation of radio waves and reduction of the scattering cross section due to electrical conductivity. As shown in Equations (6)(7)(8)(9)(10), the attenuation of radio waves varied with the frequency (or wavelength) of radio waves. A number of frequency bands in the range of 3-50 MHz are allocated to be used for oceanographic radar applications as outlined in Resolution 612 in the 2012 World The fundamental essence of SSS estimates using the HF radar is the relationship between the received power and conductivity, as shown in Figure 6b.…”

“…A number of frequency bands in the range of 3-50 MHz are allocated to be used for oceanographic radar applications as outlined in Resolution 612 in the 2012 World Radiocommunication Conference (WRC-12) [52]. Figure 14 shows the value of the attenuation coefficient A 4 for frequencies of 3 MHz, 10 MHz, 25 MHz, and 50 MHz at 10 km from the radar, as obtained by Equations (6)(7)(8)(9)(10). The attenuation values were normalized to a value of 4 S/m for each frequency.…”

“…A high-frequency (HF) radar has the unique ability to continuously monitor a wide range of sea surface current velocities and is widely used in regional-or national-level networks [1][2][3][4]. The HF radar has features that are advantageous for disaster prevention, such as the detection of tsunami currents [5][6][7] and observation of subsequent natural oscillations induced by tsunami waves [8,9]. Furthermore, recent studies have indicated that HF radars can be used to measure ocean wave parameters [10][11][12] and wind speed and direction [13][14][15], and these applications have been reviewed by Lorente et al [4].…”

Coastal Extension of CMEMS Products. Models, Data and Applications

“…HFRs present a wide range of practical applications, among others: analysis of transport processes (for search and rescue operations, oil spill emergencies, etc.) or the effective monitoring of extreme events, such as storm surges, tsunamis, typhoons, and hurricanes (Suzuki, 2015;Saramul, 2017;Miles et al, 2017;Toguchi et al, 2018;Dao et al, 2019;Lipa et al, 2019;Serra et al, 2020). Given the consolidation of this remote sensing technology, the synergistic integration of HFRs and hydrodynamic models has demonstrated to be a valid strategy to comprehensively characterize the complex coastal circulation (O'Donncha et al, 2015;.…”

On the Performance of High Frequency Radar in the Western Mediterranean During the Record-Breaking Storm Gloria

“…HFRs present a wide range of practical applications, among others: analysis of transport processes (for search and rescue operations, oil spill emergencies, etc.) or the effective monitoring of extreme events, such as storm surges, tsunamis, typhoons, and hurricanes (Suzuki, 2015;Saramul, 2017;Miles et al, 2017;Toguchi et al, 2018;Dao et al, 2019;Lipa et al, 2019;Serra et al, 2020). Given the consolidation of this remote sensing technology, the synergistic integration of HFRs and hydrodynamic models has demonstrated to be a valid strategy to comprehensively characterize the complex coastal circulation (O'Donncha et al, 2015;Lorente et al, 2019a).…”