| Section A | A index | 491-499 of 917 terms |
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analog climate model—A method of predicting future climate by comparison with a historical situation, such as a paleoclimate state, in which the climatic forcing had features similar to those anticipated in the future.
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analog method—A method of forecasting that involves searching historical meteorological records for previous events or flow patterns similar to the current situation, then making a prediction based on those past events or patterns.
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analog model—An empirical forecast model based on the use of analogs. The observed states subsequent to a previously observed analog of the current observed state can be used as a forecast.
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analog—1. A form of data display in which values are shown graphically. 2. A form of computing in which values are represented by directly measurable quantities, such as voltage or resistance. Analog computing methods contrast with digital methods in which values are treated numerically.
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analogs—Two observed states of the atmosphere that are very close by some measure, also applied to states of a model. Formal measures of closeness include anomaly correlation, root-mean-square distance, and covariance. Usually one expects analogs to occur only during the same time of year. Atmospheric analogs that are close compared to current levels of observational error are unlikely to be found unless one studies a single variable confined to a very small area (≤1000 km radius), or otherwise reduces the degrees of freedom to a very small number (≤3). Analogs have a practical application in specifying the surface weather from a 3D atmospheric state produced by NWP and in short- term climate prediction for forecasts ranging from a month to several seasons. Analogs are also of interest in research related to predictability, short-term forecasts and error growth, cluster analysis, and estimates of dimensionality of the atmospheric attractor. When natural analogs are poor, improvements have been sought by combining several of them, by using anti-analogs (antilogs), and by constructing an artificial close analog by some objective weighted averaging of a set of previously observed states (constructed analogs). See MOS, perfect prognosis method.
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analysis of variance—A statistical technique for resolving the total variability of a set of data into systematic and random components. The analysis of variance is fundamentally a statistical estimating and/or testing procedure. It estimates the components of variance due to systematic and random causes, and it leads to significance tests of these components. The statistical assumptions required for a valid test are more stringent than those for estimating the components of variance.
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analysis—1. In synoptic meteorology, a detailed study of the state of the atmosphere based on observations, usually including a separation of the entity into its component patterns and involving the drawing of families of isopleths for various elements. Thus, the analysis of synoptic charts may consist, for example, of the drawing and the interpretation of the patterns of wind, pressure, pressure change, temperature, humidity, clouds, and hydrometeors, all based on observations taken or forecast simultaneously. 2. A procedure to project the state of the atmosphere (or any system) as known from a finite set of imperfect, irregularly distributed observations onto a regular grid or to represent the atmospheric state by the amplitude of standard mathematical functions. The grid and/or functional expansion allows for subsequent forecasts by numerical integration or for easy diagnostic study. An analysis may be looked upon as a space–time interpolation system. Essential ingredients of analysis are a background field, usually a short-range forecast although persistence and climatology are options, a forecast model, knowledge of the relative error of the many different observational platforms employed as well as knowledge of the error in the background field, and the spatial covariance of the various errors. Real time computational considerations generally limit the complexity of methods used. Historically important is the subjective hand analysis, that is, drawing isobars on a map given mean sea level pressure at a set of observing stations. Most analysis systems in the past have been at best 3D spatial analyses; time–space analysis systems have recently emerged at operational prediction centers. A long series of analyses is of great utility for studying the behavior of the atmospheric climate system. See reanalysis, variational objective analysis.
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analyzed chart—Chart depicting the geographical distribution of meteorological conditions with the aid of fronts, isobars, etc.
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