HF Radar　Measurements　of 　M2 　Tidal　Current　in　Tokyo 　Bay

HF radar and Acoustic Doppler Current Profiler (ADCP) observations are made to measure the horizontal distribution of the M2 tidal current in Tokyo Bay (Japan). In order to clarify the accuracy of the HF radar-derived M2 tidal current, we compare the harmonic constants from the HF radars with those from the ADCPs at four stations. The comparison reveals that the accuracy strongly depends on the azimuthal difference in the radar beams and the distance from the HF radars due to the observational errors in the azimuthal direction. The M2 tidal current ellipse from the four HF radars are consistent with those from the ADCPs, indicating that at least four HF radars are required to monitor the M2 tidal current field in the bay. From the results from four HF radars, the phase of the M2 tidal current in the bay is generally between 60-70 degrees, while the phase proceeds at 20-40 degrees off Futtsu Point. In contrast with the previous studies, the phase in the eastern region does not proceed compared to the western region.