EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Exploring a Stratocumulus-to-Cumulus Transition: A Perturbed Parameter Ensemble of Large-Eddy Simulations

Rachel Sansom1, Lindsay Lee2, Jill Johnson3, Leighton Regayre1, and Ken Carslaw1
Rachel Sansom et al.
  • 1School of Earth and Environment, University of Leeds, UK
  • 2Advanced Manufacturing Research Centre, University of Sheffield, UK
  • 3School of Mathematics and Statistics, University of Sheffield, UK

The transition from stratocumulus to cumulus clouds that takes place as air is advected from the subtropics towards the equator causes a decrease in cloud radiative effect, with cloud fraction halving from start to finish. The transition is initiated by increasing sea surface temperatures, and it is widely agreed that the lower tropospheric stability plays a key role in the timing of the transition. In this work, we study the relative importance of five atmospheric initial conditions: specific humidity in the boundary layer and free troposphere, free tropospheric potential temperature, inversion height and initial aerosol distribution. We simulate a Lagrangian trajectory of a stratocumulus-to-cumulus transition, using the Met Office/NERC cloud model coupled with a bulk microphysics scheme and a radiation scheme. From this base simulation we make 60 perturbations to simulate the transition under different combinations of the atmospheric initial conditions mentioned. Additionally, we include a model parameter from the Khairoutdinov and Kogan autoconversion parameterisation from 2000. We discuss here the relative importance of these so-called parameters, in particular the role of aerosol, and we explore whether a much faster transition by drizzle takes place in simulations with lower aerosol concentrations. 

How to cite: Sansom, R., Lee, L., Johnson, J., Regayre, L., and Carslaw, K.: Exploring a Stratocumulus-to-Cumulus Transition: A Perturbed Parameter Ensemble of Large-Eddy Simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12007,, 2022.