increasing parallel wave number.

![The zonal flow quality ($\Omega^{IM}/\Omega^{RE}$) as a function of $k_{\parallel}$ with $\epsilon_n = 0.0$ (diamond) and $\epsilon_n = 1.0$ (square) is shown. The other parameters are $\tau = 1$, $k_x = k_y = q_x = 0.3$, $\mu = 0$ and $\eta_i = 4.0$.](Fig_3a.eps){height=".3\textheight"}

The zonal flow growth rate (positive) and real frequency (negative) (normalized to $c_s/L_n$) as a function of $k_{\parallel}$ with $\epsilon_n = 0.0$ (diamond) and $\epsilon_n = 1.0$ (square) are displayed in Figure 5. The other parameters are $\tau = 1$, $k_x = k_y = q_x = 0.3$, $\mu = 0$ and $\eta_i = 4.0$. A rapidly increasing zonal flow growth rate and real frequency is found for small parallel wave numbers and this result is corroborated with the approximate Eqs. 24 - 25 of the change in zonal flow $\Omega$. This also shows that the slab like generated zonal flows are driven by the acoustic waves through the ITG mode. This is the reason for the comparatively larger real frequency of the slab like driven zonal flow. The growth rate and real frequency for the toroidally generated zonal flows are only weakly dependent on the parallel wave number.

![The zonal flow growth rate 