Cumulus clouds and the coherent structures that trigger them

Dr Steven Boeing and Dr Leif Denby, University of Leeds. Part of the Applied Mathematics seminar series.

In the below-cloud boundary layer of the Earth's atmosphere, coherent structures of air are formed through interaction with the Earth's surface. These structures trigger the formation of convective clouds. Due to their small size relative to the current achievable computational resolution these drivers of convection must be parameterised in contemporary weather and climate models (which have
horizontal grid spacings on the order of 1-4km and 10-100km respectively). However, the growth, organisation and physical properties of these structures is currently poorly understood, making the parameterisations inaccurate. This is thought to be one of the main causes of poor weather forecasts and uncertainty in climate predictions.

Using techniques developed in mathematics (cumulants and Minkowski functionals), analysis tools have been developed during the GENESIS project to identify and quantify the properties of these coherent boundary layer structures. In this talk, we will show results of these techniques applied to archetypal simulations of shallow convection with and without ambient wind shear, delineating a path to a more physically-based representation of the formation of convective clouds.

We will also discuss ongoing efforts to model the clouds as rising thermals. Again, it appears that capturing the behaviour of the thermals near cloud base is key to understanding their behaviour. A Lagrangian method for simulating moist convection may help us generate new insights into the behaviour of the clouds as they start to form. Finally, we will show a new and exciting way of visualising cloud formation which uses a pyramid-shaped projector located at the School of Earth and Environment.