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World Weather Watch

the world-wide, coordinated system of meteorological facilities and services provided by World Meteorological Organization members for the purpose of ensuring that all members obtain the meteorological information required both for operational work and for research; the essential elements of the WWW are: the global observing system, the global data-processing system, and the global telecommunication system.


A type of Pleistocene-age (formed 1.8 million to 10,000 years before present) permafrost that contains a significant amount of organic material with ice content of 50– to 90 percent by volume. Thawing yedoma is a significant source of atmospheric methane.

A yedoma in Russia shows the thick layer of ice and carbon material exposed along this body of water. --Credit: Vladimir Romanovsky

young ice

a general category of ice that represents the transition between nilas and first-year ice; usually 10 to 30 centimeters (4 to 12 inches) thick.

Young's Modulus

the ratio of increase in stress acting on a test specimen, to the resulting increase in strain, under constant transverse stress.

zero curtain

the persistence of a nearly constant temperature, very close to the freezing point, during annual freezing (and occasionally during thawing) of the active layer.

zone of gas-hydrate stability

that portion of the subsurface where the conditions of temperature and pressure are suitable for the formation and preservation of gas hydrates.