Seasonal Variations and Long-term Trends of the Coastal Upwelling along the Southwestern Coast of the East Sea/Japan Sea

Abstract

To investigate seasonal variations and long term trends of coastal upwelling along the southwestern coast of the East Sea/Japan Sea (EJS), sea surface temperature and wind data from 1968 to 2012 were analysed based on an upwelling-related temperature signal and an upwelling index. The upwelling-related temperature signals were estimated by temperature anomaly from a temperature curve that was adapted by a fifth order polynomial with top five temperatures at every day. These signals were negatively correlated (~ 0.6) with southwesterly winds blowing parallel to the coast. In addition, the upwelling signals were closely related with primary productivities near the upwelling region in late spring to early summer, suggesting importance of upwelling on ecosystem in the EJS. The upwelling index calculated by wind shows that the upwelling occurs from April to August with the maximum in July. We found that the long-term trend of the upwelling indices were considerably different season by season: it increased in spring while decreased in summer. Based on regional climate model projection, we also found that the coastal upwelling is projected to be intensified due to an increase in the speed of upwelling-favored wind.emperature signal and an upwelling index. The upwelling-related temperature signals were estimated by temperature anomaly from a temperature curve that was adapted by a fifth order polynomial with top five temperatures at every day. These signals were negatively correlated (~ 0.6) with southwesterly winds blowing parallel to the coast. In addition, the upwelling signals were closely related with primary productivities near the upwelling region in late spring to early summer, suggesting importance of upwelling on ecosystem in the EJS. The upwelling index calculated by wind shows that the upwelling occurs from April to August with the maximum in July. We found that the long-term trend of the upwelling indices were considerably different season by season: it increased in spring while decreased in summer. Based on regional climate model projection, we also found that the coastal upwelling is projected to be intensified due to an increase in the speed of upwelling-favored wind.