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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.
Key Strengths:
- Simple time series
Key Limitations:
- Raw monthly values are noisy; need to be smoothed
- Marshall, G. J., 2003: Trends in the Southern Annular Mode from observations and reanalyses. J. Clim., 16, 4134-4143.
- Hurrell, J.W. (1995): Decadal Trends in the North Atlantic Oscillation: Regional Temperatures and Precipitation. Science 4 August 1995: Vol. 269 no. 5224 pp. 676-679
- Hurrell, J.W. and C. Deser (2009): North Atlantic climate variability: The role of the North Atlantic Oscillation. Journal of Marine Systems Volume 78, Issue 1, August 2009, Pages 28–41
- Hurrell et al. (2003) in The North Atlantic Oscillation: Climate Significance and Environmental Impact, 2003. J.W. Hurrell, Y. Kushnir, G. Ottersen, and M. Visbeck, Eds. Geophysical Monograph Series, 134, 279pp
- Trenberth, K. E., 1984: Signal versus noise in the Southern Oscillation, Mon. Wea. Rev.,. 112, 326-332
- Guttman, N.B. (1999): ACCEPTING THE STANDARDIZED PRECIPITATION INDEX: A CALCULATION ALGORITHM. Journal of the American Water Resources Association, Vol. 35, NO.2 AMERICAN WATER RESOURCES ASSOCIATION
- McRoberts, D. Brent, John W. Nielsen-Gammon, 2012: The Use of a High-Resolution Standardized Precipitation Index for Drought Monitoring and Assessment. J. Appl. Meteor. Climatol., 51, 68–83.
- Stammerjohn, S. E. et al (2008), Trends in Antarctic annual sea ice retreat and advance and their relation to El Nin ̃o – Southern Oscillation and Southern Annular Mode variability, J. Geophys. Res. , 113 , C03S90
- Heim, Jr., Richard R., 2002: A review of Twentieth-Century drought indices used in the United States. Bulletin of the American Meteorological Society, vol. 83, pp. 1149-1165.