Study On Variations In Kuroshio Path South Of Japan And Its Related Physical Phenomena

As one of the western boundary currents, Kuroshio carries large amount of heattransporting from low latitudes to high latitudes due to its specific features of volumetransports in the North Pacific. This impacts the climates and resources of countries inthe East Asia and Southeast Asia. On the other hand, variations in Kuroshio path southof Japan also impact the fishery and voyage in that region. Due to the influences ofvariations in Kuroshio path on the human activities can not be ignored, studies on thecharacteristics of variations in Kuroshio path and its related physical phenomena havesignificant senses on reducing the property loss of human, making further understandthe mechanisms of variations in Kuroshio path, and providing basic theories to highlypredict its path.In this study, several oceanic observations, including merged altimetric seasurface height (SSH), sea level from tide gauge, wind stress, sea level pressure, netsurface heat flux, sea surface temperature (SST) and subsurface temperature/salinity,are used to investigate the variations in Kuroshio path south of Japan and its relatedphysical phenomena. During this investigation, descriptions in this study focus on thefollowing interesting phenomena.It is well-known that variations in Kuroshio path south of Japan lead to changesin sea surface height; such as, there is high sea surface height when Kuroshio takestypical lager meander path. In order to make variations in sea surface height clearly,spatiotemporal characteristics and driving mechanisms of linear trend, seasonalvariations, intraannual variations and interannual variations of SSH south of Japan,based on altimetric SSH, is firstly explored. Results show that changes in seasonalsteric height, which caused by thermal expansion of water column, have vital impactson the seasonal variations of SSH. The disturbances generated in the central North Pacific, transporting westward along latitudes and Kuroshio extension jet, have greatinfluences on the intraanual SSH south of Japan. On the other hand, the disturbanceswhich have important impacts on the interannual SSH south Japan are generated inthe central and eastern North Pacific.On the other hand, changes in Kuroshio path south of Japan have closerelationship with variations in sea level at Tokara Strait, Kii Peninsula and Izu Islands.Thus, the next problem in this study focuses on the intraannual and interannualvariations in sea level at Tokara Strait, Kii Peninsula and Izu Islands using sea leveldata from tide gauge and altimetric SSH. Moreover, intraannual variations inKuroshio path at Tokara Strait and interannual changes in Kuroshio path at KiiPeninsula are also explored. Results show that the mesoscale perturbations fromupstream and downstream significantly impact the intraannual and interannualvariations of sea level at Tokara Strait, Kii Peninsula and Izu Ridge. On the other hand,oceanic mesoscale perturbations and velocity front of currents have importantinfluences on the intraannual variation of Kuroshio path at Tokara Strait andinterannual variations of Kuroshio path at Kii Peninsula.Another point addressed in this study is the interannual meridional shifts ofKuroshio path south of Japan using altimetric SSH. The mechanism and relatedoceanic phenomena of interannual meridional shifts of Kuroshio path south of Japanare also addressed. Our result shows that perturbations of interannual meridionalshifts of Kuroshio path in the upstream could have influences on the changes ofKuroshio path in the downstream. After applying EOF analysis to the time series ofinterannual meridinal shifts of Kuroshio path, results show that the principlecomponent of the first EOF mode can represent near-and off-shore non-largemeander of Kuroshio path south of Japan; while the principle component of thesecond EOF mode can represent typical large meander of Kuroshio path south ofJapan. Moreover, results obtained by linear regression show that negative sea surfaceheight anomalies, which propagate along Kuroshio extension, can significantly impactthe typical large meander of Kuroshio path south of Japan; whereas positive seasurface height anomalies, which propagate along Kuroshio extension, can vitally influence the near-and off-shore non-large meander of Kuroshio path south of Japan.On the other hand, the interannual meridional displacements of Kuroshio path playimportant roles in the spatial distributions of changes in interannual sea surfacetemperature, subsurface temperature and eddy kinetic energy.The last issue discussed in this study is to explore the spatially statistical featuresof energy conversion between eddies and mean flow and Reynolds stresses whenKuroshio path south of Japan under different states using the altimetric sea surfaceheight. Our results show that distributions of energy conversion and Reynolds stressesdepend on the states of Kuroshio path south of Japan. And these distributions mostlylocate at the eastern of Kyushu and the southeast of Kii peninsula. During the periodof Kuroshio south of Japan taking a certain path, the eddy momentum fluxes flow toKuroshio jet. On the other hand, the nonlinear instabilities of Kuroshio jet haveinfluences on the spatial distribution of eddy momentum flux. Moveover, the currentstability south of Japan also discussed under different states of Kuroshio path usingsubsurface temperature and salinity data. Results show that the baroclinic instabilitywould be easily occurred for the current system south of Japan when Kuroshio pathtaking offshore non-large meander state. when Kuroshio path south of Japan takesnear-shore nonlarge meander and typical large meander, however, the both havecomparably permissible windows for unstable wave; whereas the most unstable wavesin current system south of Japan have longer timescale under the formercircumstances.