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Section J J index 1-9 of 38 terms previous 1 2 3 4 Next J process—(Sometimes called Junction process.) The slowly propagating electrical breakdown process in a cloud carrying net charge; it can initiate a K process. See K changes. j-value—(Also known as photolysis rate.) A first-order rate coefficient (in units of inverse time) for the occurrence of a photochemical reaction. The j-value is calculated from the product of the absorption cross section of the molecule being photolyzed, the quantum yield for the process, and the actinic flux, all integrated over the wavelength region of interest. See actinometer. J–W meter—See Johnson–Williams liquid water probe. Jacob's ladder—See crepuscular rays. Jacobian—The determinant formed by the n2 partial derivatives of n functions of n variables, when the derivatives of each function occupy one row of the determinant. For the case of two functions f(x, y) and g(x, y), the Jacobian J(f, g) is sometimes also written The geostrophic advection of any scalar ψ may be written where g is the acceleration of gravity, f the Coriolis parameter, and z the isobaric contour height. January thaw—In the United States, a period of mild weather popularly supposed to recur each year, in later January; most pronounced in the Northeast and, to a lesser extent, the Midwest. The daily temperature averages at Boston, computed for the years 1873 to 1952, show a well- marked peak on 20–23 January; the same peak occurs in the daily temperatures of Washington, D.C., and New York City. Statistical tests show a high probability that it is a real singularity. The January thaw is associated with the frequent occurrence on the above-mentioned dates of southerly winds on the back side of an anticyclone off the southeastern United States. Japan Current—Same as Kuroshio. Japan Sea Deep Water—(Also called Japan Sea Proper Water.) A water mass found in the Japan Sea below a depth of 200 m (84% of the volume of the Japan Sea). Being isolated from all other oceans, it has very uniform salinity (34.1) and temperature (0°– 1°C). See deep water. Japan Sea Middle Water—A water mass found at a depth from 25 to 200 m in the Japan Sea in which the temperature drops from 17° to 2°C. It is well ventilated with a high oxygen content of 8 ml l−1. Japan Sea Proper Water—See Japan Sea Deep Water. previous 1 2 3 4 Next