fluctuations. They found a self-sustained turbulence with velocity dispersion of $\sim0.2-0.4$ km s$^{-1}$ for a period of at least their simulation time (several 10 Myr) in the bistable fluid after temporal decaying found in @KN02. External forcing such as shock compression can drive stronger long-lived turbulence. @KI02 investigated development of the TI in a shock compressed region by using a two-dimensional hydrodynamical simulation. They found that the velocity dispersion is as large as several km s$^{-1}$, which is larger than the sound speed of the CNM. The supersonic turbulent motion is maintained as long as the shock wave continutes to propagate and provide postshock gas. They suggested that this supersonic translational motion of the CNM is observed as the supersonic turbulence in the ISM. The cloudlets are precursor of molecular clouds because they are as dense as molecular clouds. After their work, many authors have investigated the formation of the CNM in shocked gases in two-dimensional calculations [@AH05; @HA07; @Hetal05; @Hetal06], and in three-dimensional calculations [@Getal05; @Vetal06; @AH10]. The influence of the magnetic field on the development of the TI has been investigated by @II08 [@II09], @Hene08, @Hetal09.

Although physics of the bistable fluid is developing, the physical mechanism of 