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Arctic Oscillation (“AO”)

28 Nov 2004 by group

Translations: (Français)

Measure of the pressure gradient between the polar and subpolar regions of the Northern Hemisphere. The term was introduced by Thompson and Wallace (2000). More information on the AO can be found here. See also North Atlantic Oscillation”(NAO”).

Filed Under: Glossary

Atlantic Multidecadal Oscillation (“AMO”)

28 Nov 2004 by group

Translations: (Français)

A multidecadal (50-80 year timescale) pattern of North Atlantic ocean-atmosphere variability whose existence has been argued for based on statistical analyses of observational and proxy climate data, and coupled Atmosphere-Ocean General Circulation Model (“AOGCM”) simulations. This pattern is believed to describe some of the observed early 20th century (1920s-1930s) high-latitude Northern Hemisphere warming and some, but not all, of the high-latitude warming observed in the late 20th century. The term was introduced in a summary by Kerr (2000) of a study by Delworth and Mann (2000).

Filed Under: Glossary

Atmosphere-Ocean General Circulation Model (“AOGCM”)

28 Nov 2004 by group

Translations: (Français)

Fully coupled atmosphere-ocean model of the three-dimensional global climate. See also ‘General Circulation Model (GCM)’.

Filed Under: Glossary

Climate Field Reconstruction (“CFR”)

28 Nov 2004 by group

Approach to reconstructing a target large-scale climate field from predictors employing multivariate regression methods. CFR methods have been applied both to filling spatial gaps in early instrumental climate data sets, and to the problem of reconstructing past climate patterns from ‘climate proxy’ data.

Filed Under: Glossary

Climate Proxy

28 Nov 2004 by group

Translations: (Français)

Climate ‘proxies’ are sources of climate information from natural archives such as tree rings, ice cores, corals, lake and ocean sediments, tree pollen, or human archives such as historical records or diaries, which can be used to estimate climate conditions prior to the modern period (e.g. mid 19th century to date) during which widespread instrumental measurements are available. Proxy indicators typically must be calibrated against modern instrumental information to yield a quantitative reconstruction of past climate.

Filed Under: Glossary

El Niño/Southern Oscillation (“ENSO”)

28 Nov 2004 by group

Translations: (Français)

A natural coupled mode of climate variability associated with both surface temperature variations tied to El Niño and atmospheric circulation changes across the equatorial Pacific (see also ‘Southern Oscillation Index’). Term was first coined by Rasmusson and Carpenter (1982). More information on ENSO can be found here.

Filed Under: Glossary

Empirical Orthogonal Function (“EOF”)

28 Nov 2004 by group

Spatial pattern tied to a particular mode of time/space variance in a spatiotemporal data set (see also “Principal Components Analysis or “PCA”).

Filed Under: Glossary

Energy Balance Model (“EBM”)

28 Nov 2004 by group

Simple climate model consisting of a uniform ocean and atmosphere that respond thermodynamically, but not dynamically, to changes in radiative forcing.

Filed Under: Glossary

Forcings

28 Nov 2004 by group

Translations: (Français)

Forcings in the climate sense are external boundary conditions or inputs to a climate model. Obviously changes to the sun’s radiation are external, and so that is always a forcing. The same is true for changes to the Earth’s orbit (“Milankovitch cycles”). Things get a little more ambigous as you get closer to the surface. In models that do not contain a carbon cycle (and that is most of them), the level of CO2 is set externally, and so that can be considered a forcing too. However, in models that contain a carbon cycle, changes in CO2 concentrations will occur as a function of the climate itself and in changes in emissions from industrial activity. In that case, CO2 levels will be a feedback, and not a forcing. Almost all of the elements that make up the atmosphere can be considered feedbacks on some timescale, and so defining the forcing is really a function of what feedbacks you allow in the model and for what purpose you are using it. A good discussion of recent forcings can be found in Hansen et al (2002) and in Schmidt et al (2004).

Filed Under: Glossary

General Circulation Model (“GCM”)

28 Nov 2004 by group

Translations: (Français)

Typically refers to a three-dimensional model of the global atmosphere used in climate modeling (often erroneously called “Global Climate Model”). This term often requires additional qualification (e.g., as to whether or not the atmosphere is fully coupled to an ocean–see ‘Atmosphere-Ocean General Circulation Model’).

The length scales that are resolved in these models is typically on the order of 100s of kilometers (i.e. features that size or smaller are not directly resolved). The timestep for the models (how often the fields are updated) is usually 20 minutes to an hour. Thus in any day there would be 24 to 72 loops of the main calculations.

The basic variables are the temperature, humidity, liquid/ice water content and atmospheric mass. The physics usually consists of advection, radiation calculations, surface fluxes (latent, sensible heat etc.), convection, turbulence and clouds. More elaborate Earth System models often contain tracers related to atmospheric chemistry and aerosols (including dust and sea salt).

Filed Under: Glossary

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