  Novel mechanisms for zonal flow (ZF) generation for both large relative
density fluctuations and background density gradients are presented. In this
non-Oberbeck-Boussinesq (NOB) regime ZFs are driven by the Favre stress, the
large fluctuation extension of the Reynolds stress, and by background density
gradient and radial particle flux dominated terms. Simulations of a nonlinear
full-F gyro-fluid model confirm the predicted mechanism for radial ZF
propagation and show the significance of the NOB ZF terms for either large
relative density fluctuation levels or steep background density gradients.
