Dr. Katsunori Sasaki of the School of Science, Hokkaido University and others reproduced the coastal water level of Japan in the entire 20th century by simulation using an ocean model, and clarified the cause of the high water level around 1950.
Due to the effects of global warming, observations since 1993 show that the average sea level on the earth as well as the coastal water level in Japan are rising.On the other hand, around 1950, there was a period when the water level along the coast of Japan was as high as it is now, but the cause has not been clarified.
Therefore, the research group conducted a simulation of sea level fluctuations in the Pacific Ocean using the ocean model ROMS in order to clarify the causes of coastal water level fluctuations in Japan in the 20th century.The target period is from 1871 to 2010, and long-term simulation research over 140 years is said to be rare in the world.
Comparing the simulation by ROMS and the observation result by the Japan Meteorological Agency, the simulation reproduces the height of the coastal water level in Japan around 1950.Furthermore, in order to investigate the cause of the fluctuation, the contributions of "wind stress", which is the force that drags the sea surface by the wind, and "hot salt flux", which is the supply of heat and fresh water from the sea surface, were investigated.
As a result, it was clarified that the recent rise in water level was caused by fluctuations in hot salt flux, while the high water level around 1950 was caused by fluctuations in wind stress.The cause of this fluctuation in wind stress is the weakening of the "Aleutian Low" that exists in the North Pacific Ocean in winter.The accompanying changes in wind changed the ocean circulation and raised the coastal water level in Japan.
In comparison with other climate model studies, it was also shown that the weakening of the Aleutian Low is not an anthropogenic change represented by global warming, but a natural change inherent in the climate.From this, it is important to understand not only the anthropogenic fluctuations but also the natural fluctuations in order to predict the future coastal water level in Japan.
Paper information:[Journal of Climate] Sea level variability around Japan during the 20th century simulated by a regional ocean model (English)
