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Mid-Holocene Climatic Optimum

Filed under: — group @ 28 November 2004

This is a somewhat outdated term used to refer to a sub-interval of the Holocene period from 5000-7000 years ago during which it was once thought that the earth was warmer than today. We now know that conditions at this time were probably warmer than today, but only in summer and only in the extratropics of the Northern Hemisphere. This summer warming appears to have been due to astronomical factors that favoured warmer Northern summers, but colder Northern winters and colder tropics, than today (see Hewitt and Mitchell, 1998; Ganopolski et al, 1998). The best available evidence from recent peer-reviewed studies suggests that annual, global mean warmth was probably similar to pre-20th century warmth, but less than late 20th century warmth, at this time (see Kitoh and Murakami, 2002).

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MSU Temperature Record

Filed under: — group @ 28 November 2004

Combinations of different channels of individual Microwave Sounding Unit (“MSU”) measurements have been used to generate a record of estimated atmospheric temperature change back to 1979, the “MSU Temperature Record”. The complex vertical weighting functions relating the the various channels of the MSU to atmospheric temperatures complicate the interpretation of the MSU data. Moreover, while MSU measurements are available back to 1979, a single, continuous long record does not exist. Rather, measurements from different satellites have been combined to yield a single long record, further complicating the interpretation of the MSU record. Direct comparisons of the MSU Temperature Record with the surface temperature record are therefore difficult. More information on the MSU Temperature Record can be found here.

North Atlantic Oscillation (“NAO”)

Filed under: — group @ 28 November 2004 - (Français)

Measure of the strength of the westerlies across the North Atlantic. Originally defined by Sir Gilbert Walker in 1932 as the difference in pressure between Ponta Delgada on the Azores and Stykkisholmur in Iceland. More information on the NAO can be found here. See also Arctic Oscillation (“AO”).

Pacific Decadal Oscillation (“PDO”)

Filed under: — group @ 28 November 2004 - (Français)

A pattern of variability in the ocean and atmosphere that appears to be centered in the extratropical North Pacific, which emphasizes decadal, rather than interannual, timescales. Term was introduced by Mantua et al. (1997). More information on the PDO can be found here.

Principal Component (“PC”)

Filed under: — group @ 28 November 2004

Time history tied to a particular mode of time/space variance in a spatiotemporal data set (see “Principal Components Analysis”).