Periodic behavior and stochastic fluctuations of solar activity: Proper orthogonal decomposition analysis

We use the Proper Orthogonal Decomposition ( POD) to investigate the spatiotemporal features of the solar activity. Daily observation in the period 1949-1996 of the green coronal emission line at 530.3 nm are used as indicators of the activity behavior. We show that few POD modes suffice in describing both the space and time main periodicities. In particular, being affected by a strongly energetic stochastic behavior, daily data are described by five POD modes, while two POD modes are enough to describe the butterfly diagram in monthly averaged data. Apart from the basic period T-0 = 11 years, using daily data we found evidences for intercycle temporal periodicities.