EGU22-4978, updated on 27 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Modeling the transition from the aerosol- to the updraft-limited cloud droplet susceptibility regime in large-eddy simulations with bulk microphysics

Matthias Schwarz1,99, Julien Savre2, Dipu Sudhakar3, Johannes Quaas3, and Annica M. L. Ekman1
Matthias Schwarz et al.
  • 1Stockholm University, Department of Meteorology, Stockholm, Sweden (
  • 2Meteorological institute, Fakultät für Physik, Ludwig-Maximilians-Universität, Munich, German
  • 3University of Leipzig, Institute for Meteorology, Leipzig, Germany
  • 99now at: Central Institute for Meteorology and Geodynamics (ZAMG), Climate Research, Vienna, Austria

As large-eddy simulations (LES), which explicitly simulate aerosol-cloud interactions, are often considered as benchmark simulations in climate science, it is necessary to critically evaluate if these high-resolution models can skillfully represent expected physical phenomena.

Here, we focus on the first aerosol indirect aerosol effect in a warm stratocumulus cloud. We investigate if the MIMICA LES (Savre et al., 2014) with a widely used bulk two-moment microphysical scheme (Seifert and Beheng, 2006) can reproduce the susceptibility regimes identified by Reutter et al., (2009). Using a parcel model, Reutter et al. (2009) showed that the cloud droplet number (Nd) responds differently to an increase in aerosol number (Na) depending on ambient updraft strength (w). In the aerosol-limited regime, enough supersaturation can be generated by the updraft motions in the atmosphere so that increasing Na leads to an increase in Nd. Conversely, in the updraft-limited regime, adding aerosol will not increase as activation is limited by the updraft strength and only increasing w will lead to an increase in Na.

In the standard setup, the LES cannot simulate the transition from the aerosol- to the updraft-limited regime. Only when implementing a renormalization procedure following Reisin et al., (1996) and, at the same time, increasing the initial droplet radius of newly activated droplets (rdi) to values large than rdi>1µm, a regime transition emerges. However, a clear recommendation for the choice of rdi cannot be made upon physical arguments at this point. Interestingly, the “arbitrarily chosen” droplet mass by Seifert and Beheng (2006) of 1*10-12kg, which corresponds to rdi≈6µm, seems to agree quite well with the expectations from parcel model simulations. The choice is, however, still arbitrary and therefore physically questionable.

A potential way to avoid this problem, which mainly occurs at high aerosol concentrations, would be to run the LES with a small enough temporal resolution (Δt≈0.1s) to explicitly resolve all relevant microphysical processes.



Reisin, T., Levin, Z., Tzivion, S., 1996. Rain Production in Convective Clouds As Simulated in an Axisymmetric Model with Detailed Microphysics. Part I: Description of the Model. Journal of Atmospheric Sciences 53, 497–520.

Reutter, P., Su, H., Trentmann, J., Simmel, M., Rose, D., Gunthe, S.S., Wernli, H., Andreae, M.O., Pöschl, U., 2009. Aerosol- and updraft-limited regimes of cloud droplet formation: influence of particle number, size and hygroscopicity on the activation of cloud condensation nuclei (CCN). Atmospheric Chemistry and Physics 9, 7067–7080.

Savre, J., Ekman, A.M.L., Svensson, G., 2014. Technical note: Introduction to MIMICA, a large-eddy simulation solver for cloudy planetary boundary layers. Journal of Advances in Modeling Earth Systems 6, 630–649.

Seifert, A., Beheng, K.D., 2006. A two-moment cloud microphysics parameterization for mixed-phase clouds. Part 1: Model description. Meteorol. Atmos. Phys. 92, 45–66.

How to cite: Schwarz, M., Savre, J., Sudhakar, D., Quaas, J., and Ekman, A. M. L.: Modeling the transition from the aerosol- to the updraft-limited cloud droplet susceptibility regime in large-eddy simulations with bulk microphysics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4978,, 2022.