Japan tsunami detected by HF radars on two continents

For the first time, strong tsunami signals have been observed in the currents monitored by SeaSonde HF coastal radars, after having been predicted 32 years ago [1]. Multiple radars on two continents 8200 km apart (in Japan and the U.S.) saw these distinctive signatures in radar spectral bands spanning a decade in frequency. Several analysis methods revealed the onset of the distinctive ~40-min-period oscillations, that were confirmed in all cases by nearby tide gages that monitor water level. Observations of the offshore tsunami radar patterns precedes their impact at the shore gages by the predicted amount, suggesting their value in warning of local expected intensities.