Critical Thinking

Kuroshio and Cannery Currents which are located at

Kuroshio ¢cÓ?Q.Jabir AL SALAMIStudent ID: 2ES17447SJanuary 30, 2018Kuroshio ¢c Jabir AL SALAMIIntroductionThe Kuroshio current is one of the largest ocean currents in the world, it is said that its ow isequivalent to about 6000 rivers the size of the Danube. Despite it constituting only about 0:1%of the total volume of the ocean, the heat and other physical parameters carried by this cur-rent northwards inuences the meteorology and hydrography throughout the northern hemisphereand consequently, plays an important role in the lives of the inhabitants of Eastern Asia in gen-eral, and the lives of shermen and farmers in particular.2 The current was named Kuroshio inJapanese (which means ‘black stream’) due to deep dark color of the warm, high salinity sea waterowing through it. The circulation systems in other Oceans are in fact quite similar to that inthe North Paci c. For instance, very similar circulations can be found in mid-latitude regions inboth the Northern and Southern Hemispheres, owing clockwise in the north and anticlockwisein the Southern Hemisphere. Such mid-latitude, large circulations are called subtropical gyres inthe oceanographic literature. The Kuroshio stream is the North Paci c counter-part to the GulfStream. Because subtropical gyres tend to intensify when moving west, the Kuroshio stream ismuch stronger than California and Cannery Currents which are located at the eastern boundariesof their geographical regions.This report will breiy discuss the dynamics of the Kuroshio current, its origins, ow patternsand spacial and temporal variations.Figure 1: Major Oceanic Currentsimage from: http://www.seos-project.eu/modules/oceancurrents/oceancurrents-c02-p01.html1Kuroshio ¢c Jabir AL SALAMIOcean GyresOcean gyres are large circulation current systems in the ocean.The gyres are like massive conveyorbelts that circulates ocean water around the whole earth. This process is also known as Thermo-haline Circulation. Those currents control and regulate the salinity, temperature and nutritionalcontent of water around the globe’s oceans.Three main forces drive the circulation of gyres: earth’s rotation, earth landmass distribution andwind patterns. Wind drag on the ocean surface, moving water along its direction and earth’s ro-tation deects the direction of surface ocean water currents by angles of about 45 degrees. This isknown as Coriolis e ect which causes objects to change direction when moving in a rotating frameof references. This e ect causes ocean currents to go clockwise in the Northern Hemisphere andcounterclockwise in the Southern Hemisphere.3Water beneath the surface is deected by smaller degrees due to the Coriolis e ect, resultingin what is known as an Ekman spiral. The distribution of landmass also greatly e ects the size,shape and dynamics of gyres. For instance, the South Paci c Gyre is exposed to large expanses ofopen ocean and is only bounded by the continents of South America and Oceania while in contrast,gyres that are more tightly bound and squeezed by land masses, such as the Indian Ocean Gyreshave a much smaller size.There are three main types of gyres: subpolar gyres, tropical gyres and subtropical gyres.Tropical gyres are present around the equator and is mainly created by wind, as the Coriolise ect is weak or non-present around at the equator, and therefore, have a much greater east-westcomponent than north-south, instead of a forming a circular pattern as it is the case with gyresforming at higher altitudes.1The majority of the world’s gyres form in between the equator and polar regions and are calledSubtropical gyres. The wind ows away from regions of high atmospheric pressure and then isdeected due to the Coriolis e ect causing gyres to rotate about mostly calm and stable regions.The Sverdrup transport intensity is balanced parallel to the equator over most of the Subtropicalgyres causing them to have strong western boundary currents owing towards the poles. Also,an interesting phenomena happens in the middle of gyres due to the wind ow driving the gyres.Ekman transport ensues in a direction perpendicular to the ow of the wind resulting in a higherseawater level around the center of a gyre. This accumulation of water produces a mounding ofwater whose height can reach up to 1 meter above mean sea level. The higher the water levelis at the center of the gyre, the steeper the slope of the mound is which produces a horizontalpressure gradient, with pressure being higher at the center. This pressure gradient causes water tomove towards lower pressure in what is known as Geostrophic ow ,eventually giving rise to Ekmanpumping, driving surface water downwards.2Kuroshio ¢c Jabir AL SALAMIWestern Boundary Currents and the KuroshioThe surface currents owing to the west of subtropical gyres, i.e. western boundary currents, areknown to ow much faster than their eastern counterparts mainly due to the Coriolis force beinggreater at the latitudes corresponding to the westerlies compared to those of the trade winds.Kuroshio is an example of a western boundary current. The Kuroshio current can be dividedinto three parts, the source region in Tokara Strain, South of Japan and the Kuroshio Extension.The Kuroshio current bifurcates from the North Equitorial Current east of the Phillipines into thenorth-owing Kuroshio Current and south-owing Minadano Current, where its ow rate reachesup to 30 Sv (1 million m3=s).4The Kuroshio current is known to occasionally intrude into the Luzon Strait south of Taiwan andcrosses the East Taiwan Channel into China Sea, where it can form loop currents in the northernSouth China Sea. During the summer months, the south-westward monsoon winds prevent theKuroshio Current from intruding the Luzon Straight.Figure 2: Southern Kuroshio CurrentPicture from : http : ==www:oc:nps:edu=paduan=OC4331=projsum=u05=cherrettkuroshio:html3Kuroshio ¢c Jabir AL SALAMIDue to cyclonic and anticyclonic eddies from the east, the path of the Kuroshio current hasbeen observed to uctuate with a period of about 100 days. When the Kuroshio current crosses theTokara Straight, the current’s volume increases up to 55 Sv and has a mean annual temperature of16oC. The ow across the Tokara Strait is similar to to what is found in the upstream KuroshioCurrent, as it is maximum in spring and summer and is minimum in fall and winter.The Kuroshio current south of the Honshu island is known for it s path uctuations. Instead ofowing close to the shore, the current can meander and take a path farther o shore path. Duringthese two states, the current can take a third relatively stable path that loops around the Izu Ridge.Once a meander state is observed, it can last from a month to over a decade.There has been several studies and proposed explanations for the meandering of the Kuroshiocurrent, most notably being the product of a Rossby lee induced by the pronounced coastline ofJapan. The current takes the meandering path during period in which the transport rate is lowand the straight path, closer to the shore, when the transport rate is high.Finally the Kuroshio leaves the Japanese coast, merges with the Oyashio current and ows easttowards the Paci c Ocean in what is called the Kuroshio Extension.Figure 3: The meandering paths of the Kuroshio current south of Japan4

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