A.L. Dzvonkovskaya

A powerful tsunami was generated by a 9.0-magnitude undersea earthquake, which epicentre was off the coast of Japan on March 11, 2011. The tsunami destructively hit the Japan-s coast and continued propagating across the whole Pacific Ocean within 24 hours after the earthquake. A unique possibility to observe a tsunami event proved the concept that modern oceanographic high-frequency (HF) radars are capable to monitor tsunami. Ocean surface current velocities were measured by two HF radars located at distinct parts of the Pacific Basin using different working frequencies. Both systems were providing continuous measurements when the tsunami reached their locations at the coasts. For the first time HF radars observed significant periodic deviations of ocean surface current velocity caused by the tsunami at distances of several tens of kilometres. The sequence of coming tsunami waves was clearly seen in the radial velocity measurements. The measurements proved a theoretical approach, which has been modelled in previous research, that a coming tsunami brings a special structure in surface current behaviour. The measurement results were also compared with the water level measurements by the tide gauges located nearby the radars. Radar and tide gauge results showed a perfect match in tsunami wave period estimation. These results and comparisons point out that there is a dependency between a tsunami wave height and a surface current velocity. Following the obtained results, one could make a conclusion that HF radars could contribute to development and improvement of tsunami warning systems