A Diagnostic Study of Pacific Basin Circulation Regimes as Determined from Extratropical Cyclone Tracks

Abstract

The interannual and intraseasonal track variability of cold season extratropical cyclones in the Pacific basin is examined using an 8 year cyclone track dataset. An EOF technique incorporating VARIMAX rotation in time is used to objectively describe the regime nature of the variations. Based upon this analysis we conclude that the cyclone behavior can be classified into six major regime types, corresponding to the positive and negative amplitude excursions of each of the first three rotated EOFS. Each of these rotated EOFs explains approximately equal fractions of the total variance. A study of the cyclone tracks for individual extreme periods confirms the existence of times where each of these patterns dominate. The average 500 mb height fields for these extreme periods have been examined and are generally consistent with the cyclone track anomalies. The resultant regime description shows strong interannual variability; however, there appears to be little obvious correlation with the ENSO signal, suggesting that a significant fraction of the interannual variability may be generated within the middle and high latitudes.