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).

 

yardang

A grooved or furrowed topographic form produced by wind abrasion acting on weakly consolidated sediments. Significant features are an elongation in the direction of the prevailing winds and strong undercutting. This is one type of indicator for paleowinds.

 

year without a summer

Term given to the exceptionally cold temperatures experienced at least in New England and Canada after the great eruption of Tambora in Indonesia in April 1815. See Stommel and Stommel (1981) and Stothers (1984).

 

Yellow Sea

A marginal sea centered at around 124 E and 37 N in the western Pacific Ocean that is distinguished traditionally although not hydrographically from the adjoining East China Sea to the south. 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 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 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, 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. See Tomczak and Godfrey (1994).

 

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.

 

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.

 

Ypresian

The first of four ages in the Eocene epoch (coincidental with the Early Eocene), lasting from 57.8 to 52.0 Ma. It is preceded by the Selandian age of the Paleocene epoch and followed by the Lutetian age.