\begin{table}%t2
%\centering
\par
\caption{Rough values of the growing time, wavelength, and phase velocity.
The characters "A'' and "C'' represent the absolute instability
and convective instability, respectively.}\label{tab2}
\begin{tabular}{cccccc}
\hline \hline
 & $R u_0$ & Type & $t_i \omega_{\rm p}$ & $\lambda/l_{\rm p}$ & $v_{\rm ph}$ \\ \hline
RUN1 & 1.0 & A & 5 & 6 & $-$2.8 \\
RUN3 & 0.3 & C & 10 & 0.9 & $-$1.1 \\ 
RUN4 & 1.0 & A & 5 & 8--10 & $-$2.8 \\ 
RUN5 & 0.3 & C & 10--30 & 1 & $-$1.1 \\ \hline
\end{tabular}
\end{table}