Baroclinic Rossby Wave And The Kuroshio East Of Taiwan

".., the sea is as dark as if an ink stick had been rubbed on its surface, and many hundreds of eddies can be seen floating downstream in succession. " Just as described the book titled Hachijo-Hikki written by a Japanese Uda, the Kuroshio-the western boundary current in the North Pacific, polewardly transporting huge amounts of warm water day and night, plays an important role in the mass and heat balance in the gyre. On the other hand, the interior ocean transfers energy to the western boundary in its particular ways, influencing and changing the mass transport and heat structure of the Kuroshio. However, due to the lack of data, people failed to attain a comprehensive and in-depth understanding how the oceanic Rossby waves put multifarious effects on the Kuroshio.Based on the PCM-1 moorings, satellite altimeter data, drifting float data, SODA data, WOAO1 data and et al., this work is focused on analyzing the relationship between the Kuroshio east of Taiwan and the first mode baroclinic Rossby wave as well as the second mode baroclinic Rossby wave, and clarifying the ways of the interior ocean influence over the Kuroshio, that is: in the form of eddies' activities, the propagation of the first mode baroclinic Rossby wave cause the 100-day fluctuation in the Kuroshio transport; in the form of thermocilne thickness' alteration, the propagation of the second mode baroclinic Rossby wave cause the interannual variation in the Kuroshio transport. In this study, many interesting results are found in the region where former researchers scarcely referred to.In the view of the first mode baroclinic Rossby wave, both anticyclonic and cyclonic eddies from the interior ocean can influence the Kuroshio east of Taiwan. The most effective area of the impinging eddies is determined to be the region of 22°-24°N, 121.75°-124°E. That is, only approach to this area can eddies further influence the Kuroshio east of Taiwan.On the other hand, the influence of eddies is complicated, and four kinds of mechanism of eddies' influence is summarized in this study. In general cases, a normal/weak anticyclonic eddy results in a higher SLD and a larger Kuroshio transport, but makes little change in the Kuroshio axis; a normal/weak cyclonic eddy only undermines the water on the positive side of the Kuroshio and makes the maximum speed axis shoreward shift, then reduces the Kuroshio transport. In special cases, if an anticyclonic eddy is strong enough to detour the Kuroshio and steer parts of the Kuroshio water to the east of the Ryukyu, it will trigger an offshore meandering of the Kuroshio axis and a low mass transport. While a northwestward propagating cyclonic eddy can entirely merged into the Kuroshio and thoroughly transformed the structure of the Kuroshio, then generates strong offshore meandering and greatly decreases the Kuroshio transport.At the same time, eddies are remarkably changing the thermal structure of the Kuroshio. Corresponding to the impinging eddies, alternative clod and warm advection bring the variations of temperature at the depth of 100m, and uplifting and depression of thermocline results in the variations of temperature at the depth of 400m. Through the analysis of SVD, the activity of eddy accounts for half of the temperature anomaly on the section perpendicular to the Kuroshio east of Taiwan.In the view of the second mode baroclinic Rossby wave, temperature anomalies subducted in the central region of North Pacific can partlyreach the east of Taiwan after 6-8 years and the influence the Kuroshio transport. In the beginning of 1970s, a "warm signal" subducted and arrived at the east of Taiwan in 1977, leading to the high Kuroshio transport in the next 12 years. And in the end of 1970s, a "cold signal" subducted and arrived at the east of Taiwan in 1989. At the same time, the wind stress curl remarkably weakened after 1989. Both the "cold signal" and the barotropical adjustment of external forcing cooperated to help the Kuroshio transfer from high transport period to low transport period.The first mode baroclinic Rossby wave is the "storm" in the ocean, changing the Kuroshio during different seasons. While the second mode baroclinic Rossby wave arouses the low-frequency variations of the Kuroshio transport.