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Japan Tsunami Current Flows Observed by HF Radars on Two Continents
Codar Ocean Sensors, 125 La Sandra Way, Portola Valley, CA 94028, USA
Codar Ocean Sensors, 1914 Plymouth St., Mountain View, CA 94043, USA
Laboratory of Marine Bioresource and Environment Sensing, Faculty of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho Hakodate, Hokkaido 041-8611, Japan
Laboratory of Physical Oceanography, Graduate School of Sciences, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan
Bodega Marine Laboratory, University of California, Davis, Bodega Bay, CA 94923, USA
Department of Geosciences & Romberg Tiburon Center, San Francisco State University, Tiburon, CA 94132, USA
* Author to whom correspondence should be addressed.
Received: 9 June 2011; in revised form: 27 July 2011 / Accepted: 28 July 2011 / Published: 3 August 2011
Abstract: Quantitative real-time observations of a tsunami have been limited to deep-water, pressure-sensor observations of changes in the sea surface elevation and observations of sea level fluctuations at the coast, which are essentially point measurements. Constrained by these data, models have been used for predictions and warning of the arrival of a tsunami, but to date no detailed verification of flow patterns nor area measurements have been possible. Here we present unique HF-radar area observations of the tsunami signal seen in current velocities as the wave train approaches the coast. Networks of coastal HF-radars are now routinely observing surface currents in many countries and we report clear results from five HF radar sites spanning a distance of 8,200 km on two continents following the magnitude 9.0 earthquake off Sendai, Japan, on 11 March 2011. We confirm the tsunami signal with three different methodologies and compare the currents observed with coastal sea level fluctuations at tide gauges. The distance offshore at which the tsunami can be detected, and hence the warning time provided, depends on the bathymetry: the wider the shallow continental shelf, the greater this time. Data from these and other radars around the Pacific rim can be used to further develop radar as an important tool to aid in tsunami observation and warning as well as post-processing comparisons between observation and model predictions.
Keywords: radar oceanography; remote sensing; current velocity measurement
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Lipa, B.; Barrick, D.; Saitoh, S.-I.; Ishikawa, Y.; Awaji, T.; Largier, J.; Garfield, N. Japan Tsunami Current Flows Observed by HF Radars on Two Continents. Remote Sens. 2011, 3, 1663-1679.
Lipa B, Barrick D, Saitoh S-I, Ishikawa Y, Awaji T, Largier J, Garfield N. Japan Tsunami Current Flows Observed by HF Radars on Two Continents. Remote Sensing. 2011; 3(8):1663-1679.
Lipa, Belinda; Barrick, Donald; Saitoh, Sei-Ichi; Ishikawa, Yoichi; Awaji, Toshiyuki; Largier, John; Garfield, Newell. 2011. "Japan Tsunami Current Flows Observed by HF Radars on Two Continents." Remote Sens. 3, no. 8: 1663-1679.