LARGE-SCALE CIRCULATION VARIABILITY OVER THE TROPICAL WESTERN NORTH PACIFIC .2. PERSISTENCE AND TRANSITION CHARACTERISTICS

The variability of the large-scale circulation over the tropical weste rn North Pacific is described within a framework defined by recurrent 700-mb circulation patterns that were defined by a fuzzy cluster analy sis. Individual cluster patterns (defined in Part I), which represent instantaneous depictions of the circulation variability, define favora ble and unfavorable regions for tropical cyclone genesis and preferred track types. The fuzzy cluster coefficients, which describe the time variability of 700-mb large-scale circulation anomalies, are used to i dentify the basic persistence properties of the recurrent, anomalous c irculation patterns. It is found that recurrent circulation patterns t hat are defined by small anomalies (i.e., close to the center of the c luster analysis phase space) are less persistent than recurrent patter ns that represent distinct circulation anomaly patterns. Furthermore, the persistence of a particular sequence of anomaly maps that pass thr ough a cluster is dependent upon the size of the cluster coefficients, which define how well the cluster pattern represents individual anoma ly maps. Analysis of transitions between clusters reveals that a rathe r limited set of transition paths exist. The most significant transiti on paths occur across a boundary within the cluster analysis phase spa ce that separates circulation patterns that represent an active monsoo n trough from patterns that represent an inactive monsoon trough. Phys ical descriptions of the significant transition paths are based upon 7 00-mb and 200-mb streamfunction and velocity potential anomalies, and anomalies of outgoing longwave radiation. The primary transition paths are found to be dependent upon interrelationships between several spa tial and temporal scales of atmospheric variability. Furthermore, spec ific relationships were found to be critical for determining which tra nsition path is followed. Secondary transition paths, which occur less frequently, are more dependent upon regional characteristics such as circulations within the tropical upper-tropospheric trough. Physical a ssociations between cluster patterns and tropical cyclone characterist ics that were defined in Part I remain intact during transitions betwe en the individual clusters. This is a significant result since the var iability of the large-scale circulation within the cluster framework, which is defined by the cluster membership coefficients, can be used t o infer sequences of persistent or transitioning circulation patterns. The potential application of the cluster framework for estimation of the stability of large-scale atmospheric circulation patterns and expe cted durations and transition paths is discussed in relation to the pr edictability of tropical cyclone characteristics.