Complex principal component analysis of sea‐level pressure over the eastern USA

Abstract

AbstractThe purpose of this study is to identify preferred areas of synoptic‐scale disturbance activity through the use of the objective analysis technique called complex principal component analysis. This technique is applied to a sea‐level pressure data set consisting of twice daily observations (00 and 12 GMT) for the months January through to March for the years 1973–1976 and 1979–1982. These months were chosen to encompass the time frame of the Genesis of Atlantic Lows Experiment (GALE) 1986. The geographical area studied extended from approximately 30°W to 120°W and 25°N to 60°N.The complex principal component analysis technique allows the detection of propagating features in the pressure data set. The eigenvalues, complex eigenvectors (components), and complex component scores are extracted from an augmented data matrix and are used to compute four measures that define the propagating features within the data set.Research has indicated a spatial relationship between cyclone and anticyclone tracks and the variance in station or sea‐level pressure, especially when the pressure data have been filtered to examine a frequency window traditionally associated with synoptic‐scale activity. The 2–10‐day period was selected for examination of synoptic‐scale activity in this study.The results of the analysis produced four components that could be given a preliminary, physical interpretation. The variability pattern produced by component 1 accounts for the movement of cyclones/anticyclones guided by the mean mid‐tropospheric flow. Component 2 represents the cold air outbreak anticyclones that move south‐eastward into the eastern USA. Component 3 is linked to the cold air outbreaks over the western USA and to cyclone movement in the eastern USA and Canada. Component 4 represents cyclones that move out of the central and southern states to become east coast systems. The results are not without ambiguities, which are discussed.