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Dynamics of Subsiding Shells in Actively Growing Clouds with Updrafts

Dynamics of Subsiding Shells in Actively Growing Clouds with Updrafts. Vishnu Nair 1 , Thijs Heus 2 and Maarten van Reeuwijk 1 1 Department of Civil and Environmental Engineering, Imperial College London, UK 2 Department of Physics, Cleveland State University, USA. Introduction.

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Dynamics of Subsiding Shells in Actively Growing Clouds with Updrafts

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  1. Dynamics of Subsiding Shells in Actively Growing Clouds with Updrafts Vishnu Nair1, Thijs Heus2 and Maarten van Reeuwijk1 1 Department of Civil and Environmental Engineering, Imperial College London, UK 2 Department of Physics, Cleveland State University, USA

  2. Introduction • Shallow cumulus convection is one of the most important unresolved processes in a Global Climate Model. • Lateral mixing and entrainment at cloud boundaries are dominant contributors towards cloud dilution and hence lifetime. • Mixing at cloud edges results in the formation of a descending shell (Heus and Jonker 2008) • Pre-conditions the properties of air entraining and detraining air • Downward flux compensates the majority of the upward flux in the cloud core Small et al 2009 2/15

  3. Aim • Ultimate aim of COMPLETE is to investigate the link between aerosols and droplets in clouds • Imperial is responsible for carrying out idealised direct simulations of cloud boundaries • Our final aim is to use a fully coupled droplet model • First objective : to develop a suitable simulation setup to study descending shells at cloud boundaries 3/15

  4. Numerical Simulations 4/15

  5. Governing equations • With the buoyancyb (~virtual potential temperature) defined as (Liquid water potential temperature) (Total water specific humidity) 5/15

  6. Simulation details • Grid: 3072 x 1536 x 1536 • Taylor Reynolds number, • Resolution, • Core updraft velocity, • Cloud buoyancy, 6/15

  7. Animation 7/15

  8. Mean buoyancy and mean vertical velocity 8/15

  9. Shell area 9/15

  10. Self-similarity of shell 10/15

  11. Characteristic flow scales 11/15

  12. Self-similarity of shell – TKE budget Not a classical self-similar flow! 12/15

  13. Universality of the shell 13/15

  14. Conclusions • Developed a case-setup to study descending shells at lateral cloud boundaries • Shell thickness increases linearly with time and accelerates ballistically • Non-classical self similar flow: • The appropriate characteristic scales are based on buoyancy • Shell velocity is dynamically unimportant • Shell thickness and minimum vertical velocity predictions give values comparable to observations 14/15 Nair et al. (2019), Dynamics of Subsiding Shells in Actively Growing Clouds with Vertical Updrafts, JAS (under review)

  15. Sneak preview – Lagrangian particles and droplets 15/15

  16. Acknowledgement • This project has received funding from the Marie-Sklodowska Curie Actions (MSCA) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no 675675).

  17. Questions?

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