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The American Meteorological Society promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. Founded in 1919, AMS has a membership of more than 14,000 professionals, ...
The expansion or spreading out of a vector field; also, a precise measure thereof. In mathematical discussion, divergence is taken to include convergence, that is, negative divergence. The mean divergence of a field F within a volume is equal to the net penetration of the vectors F through the surface bounding the volume (see divergence theorem). The divergence is invariant with respect to coordinate transformations and may be written
where ∇ is the del operator. In Cartesian coordinates, if F has components Fx, Fy, Fz, the divergence is
Expansions in other coordinate systems may be found in any text on vector analysis. In hydrodynamics, if the vector field is unspecified, the divergence usually refers to the divergence of the velocity field (see also mass divergence). In meteorology, because of the predominance of horizontal motions, the divergence usually refers to the two-dimensional horizontal divergence of the velocity field
where u and v are the x and y components of the velocity, respectively. This divergence is denoted by any of the following symbols:
where the last two quantities involve derivatives in the isobaric surface. The order of magnitude of the horizontal divergence in meteorological motions is of considerable dynamic importance: The geostrophic wind has divergence of the order of 10−6s−1; the wind field associated with migratory cyclonic systems, 10−5s−1; motions of smaller scale (such as gravity waves, frontal waves, and cumulus convection) have characteristic divergence one or two orders of magnitude greater. See balance equation, deformation; compare diffluence, curl, vorticity.
Industry:Weather
In the ocean, nighttime cooling due to longwave radiation, sensible heat flux, or latent heat flux that leads to the deepening of the transient thermocline.
Industry:Weather
In the ocean, heating from solar radiation (primarily shortwave) that can lead to transient thermoclines and the afternoon effect.
Industry:Weather
In oceanography, a difference between the heights of the two high waters and of the two low waters of a lunar day.
Industry:Weather
Once-daily tidal variations in sea level, which increase with lunar or solar declination north and south of the equator. When added to semidiurnal tides they can cause a diurnal inequality.
Industry:Weather
Daily, especially pertaining to actions that are completed within 24 hours and that recur every 24 hours; thus, most reference is made to diurnal cycles, variations, ranges, maxima, etc. The diurnal variability of nearly all of the meteorological elements is one of the most striking and consistent features of the study of weather. The diurnal variations of important elements at the earth's surface can be summarized as follows: 1) temperature maximum occurs after local noon and minimum near sunrise; 2) relative humidity and fog are the reverse of temperature; 3) wind generally increases and veers by day and decreases and backs by night (see heliotropic wind, land and sea breeze, mountain and valley wind); 4) cloudiness and precipitation over a land surface increase by day and decrease at night; over water the reverse is true, but to a lesser extent; 5) evaporation is markedly greater by day; 6) condensation is much greater at night; 7) atmospheric pressure varies diurnally or semidiurnally according to the effects of atmospheric tides.
Industry:Weather
A sample of soil that does not preserve the pore structure and bulk density of the parent material.
Industry:Weather
In general, any agitation or disruption of a steady state. In meteorology, this has several rather loose applications: 1) used for any low or cyclone, but usually one that is relatively small in size and effect; 2) applied to an area where weather, wind, pressure, etc. , show signs of the development of cyclonic circulation (see tropical cyclone); 3) used for any deviation in flow or pressure that is associated with a disturbed state of the weather, that is, cloudiness and precipitation; and 4) applied to any individual circulatory system within the primary circulation of the atmosphere. See wave disturbance, instability; compare perturbation.
Industry:Weather
In U. S. Weather Bureau historical records usage, a general weather forecast for conditions over an established geographic “forecast district. ”
Forecast districts are relatively large areas of the order of tens of thousands or hundreds of thousands of square miles.
Industry:Weather
A function F(x) yielding the probability that a stated random variable will assume some value less than or equal to any arbitrary number x. By definition, the distribution function is identically zero for all values of x below the least admissible value of the random variable, and identically unity for all values of x equal to or greater than the greatest admissible value of the random variable. Moreover, F(x2) ≥ F(x1) whenever x2 > x1. Sometimes, for the sake of clarity, the distribution function is called the cumulative distribution function. Compare probability density function.
Industry:Weather
