| Section C | C index | 741-749 of 1157 terms |
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condensation—In general, the physical process by which a vapor becomes a liquid or solid; the opposite of evaporation, although on the molecular scale, both processes are always occurring. In meteorological usage, this term is applied only to the transformation from vapor to liquid; any process in which a solid forms directly from its vapor is termed deposition, and the reverse process sublimation. In meteorology, condensation is considered almost exclusively with reference to water vapor that changes to dew, fog, or cloud. Condensation in the atmosphere occurs by either of two processes: cooling of air to its dewpoint, or addition of enough water vapor to bring the mixture to the point of saturation (that is, the relative humidity is raised to 100 percent). When either of these processes occurs, condensation ensues only if condensation nuclei or other surfaces are present. In the complete absence of such, condensation does not occur at nominal saturation. The spontaneous formation of liquid or solid droplets from water vapor (homogeneous nucleation) is opposed by the surface free-energy increase that attends the creation of new surfaces of the liquid or solid phase. Only for extreme supersaturation does this free-energy balance swing in favor of spontaneous nucleation.
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conditional distribution—The probability distribution of a particular variate (or subset of variates) when the other variates in the system considered are held fixed.
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conditional instability of the second kind—(Abbreviated CISK.) A process whereby low-level convergence in the wind field produces convection and cumulus formation, thereby releasing latent heat. This enhances the convergence and further increases convection. The atmospheric environment that favors CISK is found over warm, tropical oceans where there is an abundant supply of moisture, the Coriolis force is small, and air convergence is strong.
Charney, J. G., and A. Elliasen, 1964: On the growth of the hurricane depression. J. Atmos. Sci., 21, 69–75.
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conditional instability—1. The state of a layer of unsaturated air when its lapse rate of temperature is less than the dry-adiabatic lapse rate but greater than the moist-adiabatic lapse rate. Under such conditions a parcel of air at the environmental temperature is unstable to upward vertical displacements if it is saturated, unstable to downward displacements if it is saturated and contains cloud water, but stable to all small vertical displacements if it is unsaturated. For descending air containing only rain water, the stability depends on both the lapse rate and the drop-size distribution. This definition does not require that such a parcel be obtained by adiabatic displacement from any level. It also does not require that the energy released from latent heating (CAPE) be greater than the convective inhibition (CIN) required to bring the parcel to its level of free convection. 2. Similar to definition 1 except that it must be possible for a parcel displaced adiabatically from some level and with conservation of total water mixing ratio to attain the environmental temperature in a saturated state. The choice of usage of the term “conditional instability” has been uncertain and sometimes controversial for at least 50 years. Haurwitz defined it approximately as definition 1, and this has been most frequently accepted. However, Byers used a definition similar to definition 2. Beers separated the definition into three subdefinitions, “stable type,” corresponding to definition 1 when a moist parcel cannot be obtained, and “pseudolatent”and “real latent,” corresponding to definition 2 but with the last requiring essentially that CAPE be greater than CIN. Dutton subscribes to the Haurwitz definition, while Emanuel develops a definition similar to definition 2, but with elaboration similar to that of Beers.
Haurwitz, B., 1941: Dynamic Meteorology, McGraw–Hill
Byers, H., 1944: General Meteorology, McGraw–Hill
Beers, 1945: Atmospheric Physics. Handbook of Meteorology, eds. Berry, Bollay, and Beers
Dutton, J., 1995: Dynamics of Atmospheric Motion, Dover Press
Emanuel, K., 1994: Atmospheric Convection, Oxford Univ. Press, 580 pp.
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conditional mean—The mean value assumed by a particular variate when the other variates considered are held fixed.
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conditional probability—The probability that an event A will occur, under the assumption that another event B has occurred or will occur. The conditional probability is written  and is expressed, “the probability of A given B.”
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conditional sampling—Utilizing only that portion of a dataset that satisfies a certain criterion. For example, in the boundary layer a convective thermal could be defined as a flow structure that has an upward velocity exceeding some value for some minimum time period. If the average value of all temperature measurements that satisfy the above criterion is calculated, the result would give the average temperature in thermal updrafts. Such data analysis procedures allow investigators to study flow structures such as coherent structures that exist in the atmosphere.
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conditions of readiness—In the U.S. Navy, those preliminary measures prescribed for a given area in anticipation of hazardous and destructive weather phenomena. The conditions are IV, III, and II for possible threat of destructive winds (of force indicated) within 72, 48, and 24 hours, respectively, and condition I for imminent destructive winds within 12 hours.
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