A climate index is a simple diagnostic quantity that is used to characterize an aspect of a geophysical system such as a circulation pattern. A variety of methods have been used to derive assorted indices. Classically, selected station, grid point or regional average data have been used (eg., Southern Oscillation Index, Nino 3.4). Other indices are based upon empirical orthogonal functions (EOFs; eg., Artic Oscillation, North Atlantic Oscillation (NAO), Northern Annular Mode, (NAM)) or a rotated EOF (REOF; eg, Pacific-North American). Most indices use a single variable (eg., sea level pressure, sea surface temperature anomalies, geopotential height, precipitation) while others, such as the Palmer Drought Index (PDI) use a combination of variables (eg, temperature and precipitation). Most commonly, anomalies from an arbitrarily defined base period (eg; 1950-79) are the values used. Unfortunately, some indices are known by several names: eg, the Southern Annular Mode (SAM) is also known as the Antarctic Oscillation (AAO). Also, some indices have minor controversial issues. For example, the physical distinction from NAO and North Pacific indices is not completely agreed upon by researchers. These issues can result in user confusion. Further, use of different source data sets, different base periods and, where applicable, different normalizations can yield different index values.<p>
A number of websites provide excellent descriptions of one or more of the climate indices. In addition, some provide index data.
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National Center for Atmospheric Research Staff (Eds). Last modified 18 Dec 2020. "The Climate Data Guide: Overview: Climate Indices." Retrieved from https://climatedataguide.ucar.edu/climate-data/overview-climate-indices.
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Based at: NCAR | National Center for Atmospheric Research
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Created by: Climate Data Guide PIs and Staff