Convective Cloud Dynamics and Turbulence Interactions with Microphysical Processes and the Atmospheric Environment (CLOUDY TIME)

This project, studying Convective Cloud Dynamics and Turbulence Interactions with Microphysical Processes and the Atmospheric Environment (CLOUDY TIME) will: (i) improve understanding of microphysics-turbulence interactions using a hierarchy of sub-km models and large-eddy simulations; (ii) evaluate the 3D representation of moist convective turbulence in sub-km and km-scale models, testing turbulence parametrization schemes including coupling with microphysics; (iii) improve understanding of model uncertainty due to representation of vertical profiles; and (iv) evaluate mesoscale processes that lead to cloud organisation to inform scale-aware convection parametrization schemes. The improved understanding and evaluation in CLOUDY TIME will be informed by novel measurements and observations planned for the UK summertime convection field campaign WesCon, which aims to observe many of the relevant turbulent processes, and their relation to the environment, for the first time.

Convection leads to hazardous weather and is fundamental to the global atmospheric circulation. Modelling of convective storms is challenging due to the interaction of many processes which interact over a wide range of scales, from turbulence and microphysics, including precipitation formation, to the release of convective instability and evaporatively driven downdraughts and cold pools. The next generation of global weather and climate models will be run at km-scale grid lengths and will explicitly represent convective storms, but these models are highly sensitive to the sub-grid turbulence parametrization, even when run at finer resolutions with grid lengths less than 1 km. This sensitivity leads to biases in storm number, intensity and lifetime, and hence to errors in severe weather warnings and in the large-scale circulation. Conversely, errors on the large scale affect the timing and nature of convection, creating a complex web of interactions across scales. CLOUDY TIME aims to disentangle the controls on convection from the microscale, governed by parametrization, to the synoptic scale, governed by data assimilation and downscaling.