The Significance of Persistence Timescales of the Northern Annular Mode
An analysis is made examining persistence timescales of the Northern Annular Mode (NAM) within the ECMWF ERA40 dataset. Features in these are found to be not dissimilar to features found in previous analyses using NCEP data. A critical assessment of the wintertime tropospheric maximum in persis-tenc...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.624.6892 http://www.atmosp.physics.utoronto.ca/SPARC/SPARC2008GA/Posters/SessionB_P69_A370_Osprey.pdf |
| Summary: | An analysis is made examining persistence timescales of the Northern Annular Mode (NAM) within the ECMWF ERA40 dataset. Features in these are found to be not dissimilar to features found in previous analyses using NCEP data. A critical assessment of the wintertime tropospheric maximum in persis-tence timescales has found a link with low frequency variability. We conclude these timescales are less likely to be associated with particular meteorological events, than to the integrated effect of a number of events throughout winter. This work has further established the use of Empirical Mode Decomposition in diagnosing non-stationary modes in environmental data and in particular, those associated with the the timeseries of the NAM. 2 Theory & Methodology The horizon of predictability for weather forecasting is generally acknowledged to be less than 10 days. Beyond these times, the chaotic nature of weather reduces forecast skill considerably. However, other aspects of climate variability are more predictable: summers are generally warm and settled, winters cold and inclement. Seasonal predictions of ENSO are made which impact beyond the tropical Pacific and the North Atlantic Oscillation is known to be associated with patterns of wintertime behaviour in |
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