Climate Indices

Climate indices are simple diagnostic quantities that are used to characterize an aspect of a geophysical system such as a circulation pattern. They track droughts, ENSO events, wind patterns, internal modes of climate variability, and extreme events like wildfires and heatwaves. Climate indices play a key role in climate monitoring and prediction. The climate index overview page summarizes the philosophy of climate indices.

To find a specific climate index, jump to the search box below or click your desired index from among the blue sub-category buttons.

To see only the indices with in-depth commentary, select the "Datasets with guidance" button when using the search box.

Dataset Overviews

Climate datasets

Has expert guidance
The NAM (or Arctic Oscillation) is defined as the first EOF of NH (20°-90°N) winter SLP data. It explains 23% of the extended winter mean (December-March) variance, and it is clearly dominated by the NAO structure in the Atlantic sector. Hurrell wintertime SLP-based Northern Annular Mode (NAM) Index

  • Years of Record

  • 1899-01 to 2025-03

The NAM (or Arctic Oscillation) is defined as the first EOF of NH (20°-90°N) winter SLP data. It explains 23% of the extended winter mean (December-March) variance, and it…

Main variables and Earth System components

Atmosphere Sea Level Pressure
Overview: Climate Indices Overview: Climate Indices

  • Years of Record

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…

Main variables and Earth System components

Atmosphere Ocean

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MJO: Madden-Julian Oscillation Diagnostics MJO: Madden-Julian Oscillation Diagnostics

  • Years of Record

"The Madden–Julian oscillation (MJO) is the largest element of the intraseasonal (30–90 days) variability in the tropical atmosphere. It is a large-scale coupling between…

Main variables and Earth System components

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Asymmetry and Diversity in the pattern, amplitude and duration of El Niño and La Niña Asymmetry and Diversity in the pattern, amplitude and duration of El Niño and La Niña

  • Years of Record

El Niño and La Niña, the two phases of ENSO, are sometimes described as opposites. However, there are asymmetries in their spatial structure, amplitude, duration and…

Main variables and Earth System components

Ocean SST - sea surface temperature

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NAO DJFM Station-based Index Hurrell North Atlantic Oscillation (NAO) Index (station-based)

  • Years of Record

  • 1865-01 to 2023-06

The winter (December thru March) station-based index of the NAO is based on the difference of normalized sea level pressure (SLP) between Lisbon, Portugal and…

Main variables and Earth System components

Atmosphere Sea Level Pressure
NAO PC-based Index (DJFM) Hurrell North Atlantic Oscillation (NAO) Index (PC-based)

  • Years of Record

  • 1899-01 to 2025-03

The principal component (PC)-based indices of the North Atlantic Oscillation (NAO) are the time series of the leading Empirical Orthogonal Function (EOF) of SLP anomalies…

Main variables and Earth System components

Atmosphere Sea Level Pressure
Pacific Decadal Oscillation (PDO): Definition and Indices Pacific Decadal Oscillation (PDO): Definition and Indices

  • Years of Record

  • 1900-01 to 2015-12

The Pacific Decadal Oscillation (PDO) is defined by the leading pattern (EOF) of sea surface temperature (SST) anomalies in the North Pacific basin (typically, polewards of…

Main variables and Earth System components

Ocean SST - sea surface temperature
Amundsen Sea Low indices Amundsen Sea Low indices

  • Years of Record

  • 1959-01 to 2022-12

The Amundsen Sea Low (ASL) is a climatological low pressure center located over the extreme southern Pacific Ocean, off the coast of West Antarctica.  Atmospheric…

Main variables and Earth System components

Atmosphere Sea Level Pressure
Marshall Southern Annular Mode (SAM) Index (Station-based) Marshall Southern Annular Mode (SAM) Index (Station-based)

  • Years of Record

  • 1957-01 to 2015-09

The station-based index of the Southern Annular Mode (SAM) is based on the zonal pressure difference between the latitudes of 40S and 65S.  As such, the SAM index…

Main variables and Earth System components

Atmosphere Sea Level Pressure