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

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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

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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…

Main variables and Earth System components

Atmosphere Ocean

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

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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
Marshall Southern Annular Mode (SAM) Index (Station-based) Marshall Southern Annular Mode (SAM) Index (Station-based)

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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
Amundsen Sea Low indices Amundsen Sea Low indices

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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
QBO: Quasi-Biennial Oscillation QBO: Quasi-Biennial Oscillation

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The quasi-biennial oscillation (QBO) is a quasi-periodic oscillation of the equatorial zonal wind between easterlies and westerlies in the tropical stratosphere with a mean…

Main variables and Earth System components

Atmosphere Wind

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

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"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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Southern Hemisphere westerly jet strength and position Southern Hemisphere westerly jet strength and position

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The dynamics of the Southern Hemisphere westerly jet are described in terms of two indices, jet strength and jet latitude.  Here, these indices are defined using the…

Main variables and Earth System components

Atmosphere Wind
Multivariate ENSO Index Multivariate ENSO Index

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The Multivariate ENSO Index (MEI) is said to capture a more holistic representation of the atmospheric and oceanic anomalies that occur during ENSO events than do single-…

Main variables and Earth System components

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Palmer Drought Severity Index (PDSI) Palmer Drought Severity Index (PDSI)

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The Palmer Drought Severity Index (PDSI) uses readily available temperature and precipitation data to estimate relative dryness. It is a standardized index that generally…

Main variables and Earth System components

Land Drought
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

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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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Drought atlases from tree rings Drought atlases from tree rings

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Tree-ring drought atlases provide a paleoclimate analog to modern drought indices, most commonly the Palmer Drought Severity Index (PDSI).  Produced on a regular lat-…

Main variables and Earth System components

Land Drought
CRU sc-PDSI (self-calibrating PDSI) over Europe & North America CRU sc-PDSI (self-calibrating PDSI) over Europe & North America

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Maps of the monthly self-calibrating Palmer drought severity index (SCPDSI) have been calculated for the period 1901–2002 for the contiguous United States (20°–50°N and 130…

Main variables and Earth System components

Land Drought

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NAO PC-based Index (DJFM) Hurrell North Atlantic Oscillation (NAO) Index (PC-based)

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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

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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