Spatio-Temporal Analysis of Photospheric Turbulent Velocity Fields Using the Proper Orthogonal Decomposition

The spatio-temporal dynamics of the solar photosphere are studied by performinga proper orthogonal decomposition (POD) of line-of-sight velocity fields computed fromhigh-resolution data coming from the SOHO/MDI instrument. Using this technique, we areable to identify and characterize the different dynamical regimes acting in the system. All ofthe POD modes are characterized by two well-separated peaks in the frequency spectra. Inparticular, low-frequency oscillations, with frequencies in the range 20 – 130 μHz, dominatethe most energetic POD modes (excluding solar rotation) and are characterized by spatialpatterns with typical scales of about 3 Mm. Patterns with larger typical scales, of about 10Mm, are dominated by p-mode oscillations at frequencies of about 3000 μHz. The p-modeproperties found by POD are in agreement with those obtained with the classical Fourieranalysis. The spatial properties of high-energy POD modes suggest the presence of a strongcoupling between low-frequency modes and turbulent convection.