Ya-Yz

Yanai wave

An equatorially trapped wave that behaves like a mixture of gravity and Rossby waves. Yanai waves exhibit an eastward group velocity at all wave numbers k, although for large positive k is behaves like a Rossby wave and for large negative k like a gravity wave. For the case k=0 it is a standing wave for which the surface moves sinusoidally up and down with opposite sign on opposite sides of the equator. Fluid particles move anticyclonically around elliptical orbits. with eastward motion when the surface is elevated and westward motion when it is depressed. To be completed. See Hendershott (1981), p. 306 and Gill (1982).

Yellow Sea

A marginal sea centered at around 124$^\circ$ E and 37$^\circ$ N in the western Pacific Ocean that is distinguished traditionally although not hydrographically from the adjoining East China Sea to the south. It is also called the Huanghai Sea. The name comes from huge quantities of sediment discharged into the Bohai Gulf by the Yellow River in China. The traditional demarcation line between the Yellow and East China Seas varies but usually lies somewhere around 33$^\circ$ N. The Yellow Sea can be separated into a northern part, the aforementioned Bohai Bay, and the Yellow Sea proper to the south and east of Bohai Bay. The average depth of the Yellow Sea is 44 m. A shallow trough runs through it and can be traced south to the northern end of the Okinawa Trough in the East China Sea.

The hydrographic and circulation properties of both the Yellow and East China Seas are controlled by their proximity to the Kuroshio Current and the seasonal variation of the monsoon winds. The chief currents are a northwest trending branch of the Kuroshio called the Yellow Sea Current (or Yellow Sea Warm Current), the southward flowing China Coastal Current, and an unnamed current flowing southward along the west coast of Korea that carries low salinity water from the Bohai Gulf. Frontal regions separate the currents in this alternating flow pattern which is identifiable through the year, although the flow strength of the individual currents varies seasonally with the monsoons.

In the winter, strong northerly winds and cold, dry continental air vertically homogenize most of the Yellow and Bohai Seas. The winds also excite subtidal sea level fluctuations that propagate southward along the west coast of the sea all the way to the South China Sea. In the summer, solar forcing and weak wind mxing warm the upper part of the water column, leaving a conspicuous bottom pool of cold water called the Yellow Sea Cold Water, which is formed from the remnant winter water. The stratification usually appears in April and disappears in November. See Tomczak and Godfrey (1994), Guan (1994), Hu (1994), Jilan (1998) and Teague et al. (1998).

Yellow Sea Current

A northwestward flowing current in the central Yellow Sea that brings warm water from the Kuroshio Current with velocities that are a maximum of about 0.2 m/s at the surface and decrease rapidly with depth. This keeps the central waters several degrees warmer than those near the coast. The is also known as the Yellow Sea Warm Current. See Teague and Jacobs (2000).

Yellow Sea Warm Current

See Yellow Sea Current.

Yoshida jet

See Gill (1982), p. 460.

Younger Dryas

A post-LGM European climate regime where the retreat of the ice was reversed. The evidence for this event, which started at about 9000 BC, is strongest for the North Atlantic Basin, although there is some evidence for it in other parts of the world. The most probable hypothesis as to the cause of this involves the significant amount of glacial meltwater inducing changes in the atmosphere-ocean circulation, i.e. the outflow of low-salinity water into the subpolar North Atlantic may have affected the rate of deep-sea mixing and thus the production rate of North Atlantic Deep Water. It was preceded by the Allerod oscillation and followed by the Pre-Boreal period. See Crowley and North (1991), Broecker (1988) and Lamb (1985), pp. 371.