Obliquely Rotated Principal Components: An Improved Meteorological Map Typing Technique?

Michael B. Richman Illinois Institute of Natural Resources, State Water Survey Division, Climatology Section, Champaign, IL 61820

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Abstract

A detailed analysis of obliquely rotated principal components as a map typing technique was performed. This type of transformation does not constrain orthogonality of the vectors, allowing the components or map types the freedom to better reflect the original data set. Meteorological map types of sea level pressure, with previously known configurations, were utilized to ascertain the advantages and disadvantages of unrotated, orthogonally rotated and obliquely rotated components. The consequences of rotating varying numbers of components also were explored to determine the robustness of the two classes of rotations. Map types of sea level pressure for June through August 1971–1975 were generated and utilized successfully to stratify precipitation events which occurred during project METROMEX.

The obliquely rotated principal components were shown to be 1) superior to other rotational methods in retrieving input fields of synoptic scale data and, 2) less likely to distort the map types when an incorrect number of components were rotated. The obliquely rotated components proved to be a powerful data reduction technique and exhibited potential as a forecast tool since the probability of a specific weather event could be associated with a particular weather pattern.

Abstract

A detailed analysis of obliquely rotated principal components as a map typing technique was performed. This type of transformation does not constrain orthogonality of the vectors, allowing the components or map types the freedom to better reflect the original data set. Meteorological map types of sea level pressure, with previously known configurations, were utilized to ascertain the advantages and disadvantages of unrotated, orthogonally rotated and obliquely rotated components. The consequences of rotating varying numbers of components also were explored to determine the robustness of the two classes of rotations. Map types of sea level pressure for June through August 1971–1975 were generated and utilized successfully to stratify precipitation events which occurred during project METROMEX.

The obliquely rotated principal components were shown to be 1) superior to other rotational methods in retrieving input fields of synoptic scale data and, 2) less likely to distort the map types when an incorrect number of components were rotated. The obliquely rotated components proved to be a powerful data reduction technique and exhibited potential as a forecast tool since the probability of a specific weather event could be associated with a particular weather pattern.

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