Nontidal sea level changes in Hiroshima Bay,Japan

摘要

Nontidal sea level changes generated in Hiroshima Bay of the Seto-Inland Sea in Japan are studied over various time scales, from the sub-tidal(2 d to 1 month) to inter-annual scales(>2 years). The total sea level variation produces a standard deviation(STD) of 12.5 cm. The inter-annual component of the sea level variation in Hiroshima Bay oscillates with a STD of 3.4 cm, forming a long-term trend of 4.9 mm/a. The STD of the sea level variation is 9.8 cm for the seasonal component(8 months to 2 years) and 4.7 cm for the intra-seasonal one(1 month to 8 months). Significant sea level variations with a STD of 4.2 cm also occur in the sub-tidal range. Special attention is paid to the sub-tidal sea level changes. It is found that the upwelling and associated transient sea level changes generated along the north coast of Hiroshima Bay(opened southward) by the strong northerly wind, play a significant role in sub-tidal sea level changes. The transient sea level changes are over 10 cm in most cases when caused by typhoons that pass through the Pacific Ocean off the Kii Peninsula, located at about 400 km east of Hiroshima Bay. Reasonable sea level changes are evaluated by the balance of pressure forces at the onshore and offshore boundary of the study domain.