The PMD dynamics in aerial fiber can be well modeled by highly mode coupled wave-plates via the mode coupling angle fluctuation described by a Gaussian probability transition function. The RMS mode orientation angle undergoes a Brownian motion in aerial fiber. The fitting parameter K is easily measured and used as a single quantity to describe the dynamical nature of a field optical fiber with sufficient statistics. This allows industry to measure and quantify SOP and PMD correlation when field testing optical fibers. We find the K value for aerial fiber is about an order of magnitude larger than that of the buried fiber.