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Kuroshio Current Starring: LT R. Corey Cherrett, USN September 14, 2005 OC4331.

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Presentation on theme: "Kuroshio Current Starring: LT R. Corey Cherrett, USN September 14, 2005 OC4331."— Presentation transcript:

1 Kuroshio Current Starring: LT R. Corey Cherrett, USN September 14, 2005 OC4331

2 1.Geography and General Circulation 2.Four Segments of the Kuroshio Current a.Philippine Sea Including South China Sea Intrusion b.East China Sea c.Northern Philippine Sea / Japanese Coastline d.Pacific Ocean and the Kuroshio Extension 3. Kuroshio Bend/South China Sea Intrusion 4. References 5. Questions? Overview

3 Geography/Bathymetry

4 Kuroshio General Circulation North Equatorial Current flows westward into Philippine coast at Luzon. NEC divides into 2 currents: 1. Southward Current is called the Mindanao current. 2. Northward Current is the beginning of the Kuroshio Current. Kuroshio flows near: 1. Luzon (Philippine Sea) 2. Taiwan (Philippine Sea) 3. Okinawa (East China Sea) 4. Japan (Philippine Sea) 5. Into open Pacific Ocean

5 Kuroshio General Circulation Discuss current in Four Segments 1.Philippine Sea / South China Sea Intrusion 2.East China Sea 3.Philippine Sea near Japan 4.Pacific Ocean and the Kuroshio Extension

6 Segment 1: Philippine Sea and SCS Intrusion KC flows northward to the east of Taiwan. Intermittently has a loop current that flows into and back out of the South China Sea through the Luzon Strait. Kuroshio loop AKA Kuroshio Bend This loop current will ‘shed’ anti-cyclonic eddies. This will be discussed further later in the brief.

7 Segment 2: East China Sea ECS contains a broad continental shelf. Climate makes ECS water cool and fresh. This makes for a large contrast with the warm and saline subtropical mode water that dominates the Kuroshio. KC enters through the East Taiwan Channel. KC Flows NE along shelf break to 30 deg N. KC splits: 1. Westward split flows into Sea of Japan (Tsushima Current) and the Yellow Sea. 2. Eastward current (KC) flows through Tokara Strait.

8 Segment 2: East China Sea Journal of Marine Systems 24 (2000) 132 KC collision with shelf catapults subsurface KC water onto shelf floor. Warm pools (T-S properties associated with KC water) observed to encircle ECS waters (see figure right). Current vectors from sb- ADCP concur CCW circulation (fig not shown). Convergence south of cold pools. This process allows some entrainment of ECS water into the Kuroshio. Important chemical/biological exchanges. ~7% of heat and salt lost to the marginal seas through these exchanges. KC influenced by Kyushu coastal shoaling topography at about 30 N causing anti-cyclonic turning of KC and some split flow to NW (see fig below). Temperature at 50m depth KC

9 Segment 3: Philippine Sea Near Japan As the KC flows east of the Tokara Strait, it feels the shelf break, experiences vertical stretching, and turns cyclonically towards the north along the topography. The KC then follows the Japanese coastline until about 136 E. N-type – straight path. Lifespan~2.6 months A-type – Large Meander-flow breaks away from coast at Shionomisaki, does a full loop, then exits the basic north of Hachijojima Is. Lifespan~12.7 months. B-type – Large Meander, closer to Izu Ogasawara Ridge, with northward flow along and over ridge. Lifespan~1 month. C-type – Large Meander with exit south of Hachijojima Is. Lifespan~1 month. Journal of Physical Oceanography, 17 (1987) 66 23.6% 17.9%13.1% 35.9% % indicates frequency of path being occupied NA B C Large Kuroshio Meander: This feature of the KC has historically not been well modeled and is unique for the KC. Drifter data shows 4 typical states of the KC Large Meander. Data from 1955-1984. Behavior attributed to Rossby lee wave excited by the southward projection of the Kyushu coastal geometry and fixed length scale determined by Kyushu and Izu Ogasawara Ridge enclosing the basin.

10 Segment 3: Philippine Sea Near Japan A small/trigger meander first forms off the southern tip of Kyushu. That meander is advected downstream until it reaches the Kii Peninsula. Then the meander rapidly grows forming the Large Meander. Current speeds vary from 0.65 to 1.45 m/s with the maximum located just south of Shikoku. With the proximity of the KC so close to the Japanese Coast, there is very limited horizontal transport for the water that makes up the interior of the meander and therefore is explained by upwelling. 1 st operational and successful prediction of Large Meander formation was the summer of 2004, JMA.

11 Segment 4: Pacific Ocean and the Kuroshio Extension KC transitions into Kuroshio Extension at about 35 N Oyashio current also flows eastward parallel to KC. Two semi-permanent anticyclonic meanders near 144E and 150E. Bifurcation of KC near the Shatsky Rise. Region of high EKE ends at approximately the Emporor Seamounts Region of high eddy energy Gulf Stream Region of high eddy energy Source:

12 Segment 1: Philippine Sea and SCS Intrusion Revisit SCS Intrusion

13 Segment 1: Philippine Sea and SCS Intrusion Anticyclonic Rings from the Kuroshio in the South China Sea Li Li, Worth D. Nowlin, Jr., Su Jilan Observations: Northeastern South China Sea Circulation Cooperative Study, Aug ‘94 4 vessels collected data from SeaBird CTD’s at 1000db or near bottom. Some overlap for comparison. Refer to the chart below for the stations collected. Most of the obs for the ring were collected by R/V XYH14 which was equipped with an ADCP and GPS. This system measured currents underway from depths for about 10 to 250 m in 4 m depth bins. 5 minute averages were recorded. Next slide shows vertical profile through eddy and correspondes to the cross section labeled with a red line on this chart.

14 Segment 1: Philippine Sea and SCS Intrusion This figure clearly shows warm core features. Vertical depressions of more than 150 m relative to the surrounding water through the upper 500 m. (ie/20 deg C isotherm at 270 m at core, 120 m at edge. Isohaline less depressed… temperature dominates density distribution. Upper 100 m showed uniform temperature, but highly stratified salinity. Salinity in KC ~ 34.9 (plot not shown) Salinity in SCS >34.7 Salinity in core was 34.81. Since no water in the SCS has that high salinity, it strongly suggests KC origin. Core location: 21.5 N, 117.5 E Length ~ 180km X 120km Temperature change at 200db ~ 6 deg C from core to edge. Density changes ~ 1.4. Max velocity ~.88 m/s on south wall where geopotential gradient was largest.

15 Segment 1: Philippine Sea and SCS Intrusion Conclusions Have identified warm-core, anticyclonic ring. Because maximum speeds (~1 m/s) and vertical extent(>1000m) of the observed ring were close to values for the KC in the Luzon Strait, and that the KC is the only known strong oceanic current, the KC seems the only possible source. Also, an eddy feature south of Taiwan apparent at 1000db (not shown). Another paper byJia and Liu (2004) determined: Shedding occurs between 3 and 4 times/year (interval between 40 and 230 days, mostly 70 to 90 days). No seasonal variation. Location between 118 E – 120.5 E (mostly 119.5 E – 120 E). Shedding criteria includes: two centers of high SSH (one with eddy, other east of Luzon Strait), and positive geostrophic vorticity between high SSH centers. Error caused by tidal correction made it difficult to track using altimetry data.

16 REFERENCES Y. Hsueh, Journal of Marine Systems, “The Kuroshio in the East China Sea”, 24, 131-139, 2000 Li Li, Worth D. Nowlin, Jr., Su Jilan, “Anticyclonic Rings from the Kuroshio in the South China Sea”, Deep Sea Research I, 45, 1469-1482, 1998 Yinglai Jia, Qinyu Liu, “Eddy Shedding from the Kuroshio Bend at Luzon Strait”, Journal of Oceanography, 60, 1063-1069, 2004 Tangdong Qu, Humio Mitsudera, Bo Qiu, “A Climatological View of the Kuroshio/Oyashio System East of Japan”, Journal of Physical Oceanography, 31, 2575-2589,2 2001 Nikolai Maximenko, “Index and Composites of the Kuroshio Meander South of Japan”, Journal of Oceanography, 58, 639-649, 2002 Jong-Hwan Yoon, Ichiro Yasuda, “Dynamics of the Kuroshio Large Meander: Two-Layer Model”, Journal of Physical Oceanography, 17, 66-81, 1987 / Presentation for OC 4331, 2002, given by AuChuan Ong, Nick Vincent

17 Questions?

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