Physics of Scale Selection for Mesoscale Patterns in Drift Wave Turbulence*

Recently, a spatially quasi-periodic and temporally long-lived ExB pattern was reported in numerical and experimental works. A theoretical model was then developed and found that a positive feedback process drives the staircase formation via a Rhines scale dependent mixing length. The main questions are: What is the principal feedback loop physics? In this work, we study several shearing feedback mechanisms and compare them to the Rhines scale loop. The preliminary results show that nonlinear density gradient dependence of mixing length is key loop. Surprisingly, shearing feedback is in-effective. Moreover, the emergence of staircases as well as the sustainment of staircase structure, are very sensitive to the driving and damping parameters. Furthermore, we also find that the initial condition has significant effects on staircase structure. Increasing the initial mean vorticity (mean shear) weakens the staircase by suppressing drift waves, and inputting a spatially oscillating (zonal) initial shear pattern produces a persistent footprint on the staircase pattern.