\begin{table}
%\centering
\par
\caption{Summary of the initial physical parameters characterizing the
simulations.}
\label{tab1}
\begin{tabular}{llll}
\hline
\hline
 & Temperature~ & Density~~~ & Velocity \\
\hline\noalign{\smallskip}
{\em ISM} & $10^4$ K & $0.1$~cm$^{-3}$ & 0.0 \\
{\em Cloud} & $10^3$ K & $1.0$~cm$^{-3}$ & 0.0 \\
{\em Post-shock medium:} \\
 ~~~~~ - Mach 30 shock & $1.7\times 10^6$ K & $0.4$~cm$^{-3}$ & $250$~km s$^{-1}$ \\
 ~~~~~ - Mach 50 shock & $4.7\times 10^6$ K & $0.4$~cm$^{-3}$ & $430$~km s$^{-1}$ \\
\hline
\end{tabular}
\end{table}