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, lambda(1), 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 lambda(1) and the relative dispersion exponent, lambda(p), as well as to the inverse Lagrangian integral time scale tau(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 lambda(1) are found not to coincide with the regions which contribute most to the relative dispersion of particles. (C) 1996 American Institute of Physics.