Lyapunov exponents and particle dispersion in drift wave turbulence

The Hasegawa‐Wakatani model equations for resistive drift waves are solved numerically for a range of values of the coupling due to the parallel electron motion. The largest Lyapunov exponent, λ1, is calculated to quantify the unpredictability of the turbulent flow and compared to other characteristic inverse time scales of the turbulence such as the linear growth rate and Lagrangian inverse time scales obtained by tracking virtual fluid particles. The results show a correlation between λ1 and the relative dispersion exponent, λ p , as well as to the inverse Lagrangian integral time scale τ i −1. A decomposition of the flow into two distinct regions with different relative dispersion is recognized as the Weiss decomposition [J. Weiss, Physica D 48, 273 (1991)]. The regions in the turbulent flow which contribute to λ1 are found not to coincide with the regions which contribute most to the relative dispersion of particles.