Cluster analysis of the Northern Hemisphere wintertime 500-hPa height field: Spatial patterns
- Univ. of Washington, Seattle, WA (United States)
Hierarchical cluster analysis is performed on the Northern Hemisphere wintertime 10-day low-pass-filtered 500-hPa height field, using the NMC operational analyses for the period 1964--85. Input data are gridded fields at 5-day intervals, a total of 702 maps, each with 445 grid points. The measure of similarity between maps is the squared height difference, averaged over all grid points. The closest two of the maps are merged to form a cluster that, in subsequent calculations, replaces the two clusters. This procedure is repeated until all maps have been merged to form a single cluster whose centroid corresponds to the climatological mean map. The history of merging is represented in terms of a family tree that is traced back to the point where the clusters become too small to be of practical interest. The reproducibility of the larger clusters is compared by seeing how well various ones are replicated when the analysis is repeated on randomly chosen halves of the dataset in an ensemble of 50 runs. The three most reproducible clusters, which together account for [approximately]1/3 of the 702 maps in the dataset, can be reconstructed remarkably well from linear combinations of the two leading EOFs of the covariance matrix. They are related to features of the probability density function in a two-dimensional phase space defined by the expansion coefficients of these EOFs. One is marked by a closed anticyclone over the southern tip of Greenland, one by a ridge over the Gulf of Alaska, and one by a ridge over the Rockies. In comparison to other clusters of comparable size, their centroids are conspicuously far from the climatological mean map. Positive 500-hPa height anomalies in excess of 200 m are observed in association with the first two clusters, over regions of large variance and strong positive skewness of the 500-hPa height field. The results are compared with those obtained in other studies, based on variety of analysis techniques. 38 refs., 4 tabs., 17 figs.
- OSTI ID:
- 5606392
- Journal Information:
- Journal of the Atmospheric Sciences; (United States), Vol. 50:16, Issue 16; ISSN 0022-4928
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ATMOSPHERIC CIRCULATION
MATHEMATICAL MODELS
NORTHERN HEMISPHERE
EARTH ATMOSPHERE
GREENLAND
GULF OF ALASKA
MAPS
METEOROLOGY
PHASE SPACE
PROBABILISTIC ESTIMATION
ROCKY MOUNTAINS
SEASONAL VARIATIONS
USA
DEVELOPED COUNTRIES
EARTH PLANET
MATHEMATICAL SPACE
MOUNTAINS
NORTH AMERICA
PACIFIC OCEAN
PLANETS
SEAS
SPACE
SURFACE WATERS
VARIATIONS
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