Stellar winds are one of several ways that massive stars can affect the star formation process on local and galactic scales. In this paper we investigate the numerical resolution needed to inflate an energy-driven stellar wind bubble in an external medium. We find that the radius of the wind injection region, rinj, must be below a maximum value, rinj, max, in order for a bubble to be produced, but must be significantly below this value if the bubble properties are to closely agree with analytical predictions. The final bubble momentum is within 25 per cent of the value from a higher resolution reference model if χ = rinj/rinj, max = 0.1. Our work has significance for the amount of radial momentum that a wind-blown bubble can impart to the ambient medium in simulations, and thus on the relative importance of stellar wind feedback.

Using the adaptive mesh refinement code mg, we perform hydrodynamic simulations of the interaction of a shock with a molecular cloud evolving due to thermal instability (TI) and gravity. To explore the relative importance of these processes, three case studies are presented. The first follows the formation of a molecular cloud out of an initially quiescent atomic medium due to the effects of TI and gravity. The second case introduces a shock whilst the cloud is still in the warm atomic phase, and the third scenario introduces a shock once the molecular cloud has formed. The shocks accelerate the global collapse of the clouds with both experiencing local gravitational collapse prior to this. When the cloud is still atomic, the evolution is shock dominated and structures form due to dynamical instabilities within a radiatively cooled shell. While the transmitted shock can potentially trigger the TI, this is prevented as material is shocked multiple times 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 through low-density regions in the inter-clump medium. The clumps are accelerated and deformed as the flow induces clump–clump collisions and mergers that collapse under gravity. For a limited period, both shocked cases show a mixture of Kolmogorov and Burgers turbulence-like velocity and logarithmic density power spectra, and strongly varying density spectra. The clouds presented in this work provide realistic conditions that will be used in future feedback studies.

The gravity wave drag parametrization of the Whole Atmosphere Community Climate Model (WACCM) has been modified to include the wave-driven atmospheric vertical mixing caused by propagating, non-breaking, gravity waves. The strength of this atmospheric mixing is represented in the model via the ‘effective wave diffusivity’ coefficient (Kwave). Using Kwave, a new total dynamical diffusivity (KDyn) is defined. KDyn represents the vertical mixing of the atmosphere by both breaking (dissipating) and vertically propagating (non-dissipating) gravity waves. Here we show that, when the new diffusivity is used, the downward fluxes of Fe and Na between 80 and 100 km largely increase. Larger meteoric ablation injection rates of these metals (within a factor 2 of measurements) can now be used in WACCM, which produce Na and Fe layers in good agreement with lidar observations. Mesospheric CO2 is also significantly impacted by the additional source of vertical mixing, with the largest CO2 concentration increase occurring between 80-90 km, where model-observation agreement improves. However, in regions where the model overestimates CO2 concentration, the new parametrization exacerbates the model bias. The summer mesopause in both hemispheres cools significantly, by up to 35 K, and shifts upward, partially correcting the WACCM low summer mesopause. Our results highlight the far-reaching implications and the necessity of representing vertically propagating, non-breaking, gravity waves in climate models. This method way of modelling gravity waves contributes to growing evidence that it is time to move away from dissipative-only gravity wave parametrizations.

We investigate the resolution dependence of H ii regions expanding past their Strömgren spheres. We find that their structure and size, and the radial momentum that they attain at a given time, is in good agreement with analytical expectations if the Strömgren radius is resolved with dr ≤ 0.3 Rst. If this is not satisfied, the radial momentum may be over- or under-estimated by factors up to 10 or more. Our work has significance for the amount of radial momentum that a H ii region can impart to the ambient medium in numerical simulations, and thus on the relative importance of ionizing feedback from massive stars.