  A theoretical interpretation of numerically generated probability density
functions (PDFs) of intermittent plasma transport events in unforced zonal
flows is provided within the Charney-Hasegawa-Mima (CHM) model. The governing
equation is solved numerically with various prescribed density gradients that
are designed to produce different configurations of parallel and anti-parallel
streams. Long-lasting vortices form whose flow is governed by the zonal
streams. It is found that the numerically generated PDFs can be matched with
analytical predictions of PDFs based on the instanton method by removing the
autocorrelations from the time series. In many instances the statistics
generated by the CHM dynamics relaxes to Gaussian distributions for both the
electrostatic and vorticity perturbations, whereas in areas with strong
nonlinear interactions it is found that the PDFs are exponentially distributed.
