## Sweeping decorrelation in isotropic turbulence

Tennekes (J. Fluid Mech. {bold 67}, 561 (1975)) estimated the time decorrelation of inertial-range excitation in isotropic turbulence by assuming effective statistical independence of the one-time distributions of inertial-range and energy-range excitation. This picture has been challenged by Yakhot, Orszag, and She (Phys. Fluids A {bold 1}, 184 (1989)), who studied forced turbulence by renormalization-group (RNG) methods. The analysis given in the present paper leads to the conclusion that (a) precise coherence between energy-range and inertial-range excitation is needed to inhibit sweeping effects; (b) in the case of randomly forced turbulence, this coherence is impossible and Tennekes' picture is unavoidable;more »