q 2000 American Meteorological Society Annular Modes in the Extratropical Circulation. Part II: Trends*
The authors exploit the remarkable similarity between recent climate trends and the structure of the ‘‘annular modes’ ’ in the month-to-month variability (as described in a companion paper) to partition the trends into components linearly congruent with and linearly independent of the annular modes....
| Main Authors: | , , , |
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| Other Authors: | |
| Format: | Text |
| Language: | English |
| Published: |
1999
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| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.628.3078 http://www.atmos.colostate.edu/ao/ThompsonPapers/ThompsonWallaceHegerl.pdf |
| Summary: | The authors exploit the remarkable similarity between recent climate trends and the structure of the ‘‘annular modes’ ’ in the month-to-month variability (as described in a companion paper) to partition the trends into components linearly congruent with and linearly independent of the annular modes. The index of the Northern Hemisphere (NH) annular mode, referred to as the Arctic Oscillation (AO), has exhibited a trend toward the high index polarity over the past few decades. The largest and most significant trends are observed during the ‘‘active season’ ’ for stratospheric planetary wave–mean flow interaction, January– March (JFM), when fluctuations in the AO amplify with height into the lower stratosphere. For the periods of record considered, virtually all of the JFM geopotential height falls over the polar cap region and the strengthening of the subpolar westerlies from the surface to the lower stratosphere,;50 % of the JFM warming over the Eurasian continent,;30 % of the JFM warming over the NH as a whole,;40 % of the JFM stratospheric cooling over the polar cap region, and;40 % of the March total column ozone losses poleward of 408N are linearly congruent with month-to-month variations in the AO index. Summertime sea level pressure falls over the Arctic basin are suggestive of a year-round drift toward the positive polarity of the AO, but the evidence is less conclusive. Owing to the photochemical memory inherent in the ozone distribution, roughly half the ozone |
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