A synthetic jet actuator (SJA) is a zero-net-mass-flux device that imparts fluid momentum and is useful for active flow control (AFC). In many applications, airfoil performance is often limited or degraded by flow separation which is usually associated with loss of lift, increased drag, and kinetic energy losses. Therefore, it is of interest to investigate methods of separation region suppression with the forcing control of SJA. This paper studies the flow behavior of cross flow over an airfoil and how the addition of SJA influences flow characteristics. Using the Spectral Proper Orthogonal Decomposition and LES simulation, flow instabilities in the wake region are analyzed in their different temporal and spatial scales. The objective of this study is to explore the viability of SPOD for separation control and correlating the decomposed flow modes to the aerodynamic performance of airfoil.