|F(\phi_i)|} \\
\gamma_{\rm k} &=& \frac{\sum_i |F(\phi_i)| (\phi_i-\mu)^4}{\sigma^4 \sum_i |F(\phi_i)|},\end{aligned}$$ where $\phi_i$ is the Faraday depth of the $i$-th bin and, $$\mu = \frac{\sum_i |F(\phi_i)| \phi_i}{\sum_i |F(\phi_i)|},$$ is the average Faraday depth. We note that we take the definition for the kurtosis so as to the gaussian function equals to 3. We calculate the probability distribution functions of these quantities, using 800 FDFs with different configuration of turbulence, for each model.

The probability distribution functions and the 68% confidence intervals for the standard deviation, skewness, and kurtosis are shown in Figures \[fig:f9\] - \[fig:f11\], respectively. The most obvious difference can be seen in the probability distribution of the standard deviation, where Models 2 and 4 have larger values. This can be ascribed to the fact that the Faraday depth tends to reach large absolute values, although the physical reason is different between Model 2 and Model 4. As to Model 2, it is due to the presence of the coherent vertical magnetic field which pushes up the Faraday depth to large values. Contrastingly, as to Model 4, the Faraday depth behaves like random walk but the extended thermal electrons increase the expectation value of the variance of the Faraday depth.

