16'
title: Structure of dynamical condensation fronts in the interstellar medium 
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hydrodynamics - ISM: clouds - ISM: kinematics and dynamics

Introduction
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It is well known that in the interstellar medium (ISM), a clumpy low-temperature phase \[cold neutral medium (CNM)\] and a diffuse high-temperature phase \[warm neutral medium (WNM)\] can coexist in pressure equilibrium as a result of the balance of radiative cooling and heating owing to external radiation fields and cosmic rays [@Fetal69; @Wetal95; @Wetal03]. The CNM of atomic gas is observed as HI cloud ($n\sim10-100$ cm$^{-3}$, $T\sim10^2$ K). These two phases are thermally stable. On the other hand, the thermal instability (TI) arises in the temperature range between these two phases. Thus, the ISM in atomic phase can be interpreted as bistable fluid.

Pioneering work on the TI has been done by @F65 who performed a linear analysis of the thermal equilibrium gas and derived a simple criterion for the TI. Focusing on a fluid element, @B86 derived a criterion for the TI of thermal non-equilibrium gas. In the nonlinear evolution, @IT08 found a family of self-similar solutions describing the condensation of radiative gas layer assuming a simple power-law cooling rate. @IT09 investigated the linear stability 