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Using the adaptive mesh refinement code MG, we perform hydrodynamicsimulations of the interaction of a shock with a molecular cloud evolving dueto thermal instability and gravity. To explore the relative importance of theseprocesses, three case studies are presented. The first follows the formation ofa molecular cloud out of an initially quiescent atomic medium due to theeffects of thermal instability and gravity. The second case introduces a shockwhilst the cloud is still in the warm atomic phase, and the third scenariointroduces a shock once the molecular cloud has formed. The shocks acceleratethe global collapse of the clouds with both experiencing local gravitationalcollapse prior to this. When the cloud is still atomic, the evolution is shockdominated and structures form due to dynamical instabilities within aradiatively cooled shell. While the transmitted shock can potentially triggerthe thermal instability, this is prevented as material is shocked multipletimes on the order of a cloud crushing time-scale. When the cloud is molecular,the post-shock flow is directed via the pre-existing structure throughlow-density regions in the inter-clump medium. The clumps are accelerated anddeformed as the flow induces clump-clump collisions and mergers that collapseunder gravity. For a limited period, both shocked cases show a mixture ofKolmogorov and Burgers turbulence-like velocity and logarithmic density powerspectra, and strongly varying density spectra. The clouds presented in thiswork provide realistic conditions that will be used in future feedback studies.

Interactions of a shock with a molecular cloud at various stages of its evolution due to thermal instability and gravity