Evolution of the acceleration field and a reformulation of the sweeping decorrelation hypothesis in two-dimensional turbulence.

From simulations of two-dimensional inverse energy cascading turbulence, we show that points with low acceleration values are predominantly advected by the local fluid velocity. The fluid velocity u in the global frame and the fluid velocity u in the frame moving with a low-acceleration point are approximately statistically independent. This property remains valid in high-acceleration regions but only in the direction of the local acceleration vector. In the perpendicular direction, the acceleration velocity V_a=u-xi is approximately independent of xi everywhere. These statistical independences constitute our formulation of the sweeping decorrelation hypothesis for two-dimensional inverse energy cascading turbulence.