Aerosol effects on deep convection: the propagation of aerosol perturbations through convective cloud microphysics

Abstract

Abstract. The impact of aerosols on ice- and mixed-phase processes in deep convective clouds remains highly uncertain, and the wide range of interacting microphysical processes is still poorly understood. To understand these processes, we analyse diagnostic output of all individual microphysical process rates for two bulk microphysics schemes in the Weather and Research Forecasting model (WRF). We investigate the response of individual processes to changes in aerosol conditions and the propagation of perturbations through the microphysics all the way to the macrophysical development of the convective clouds. We perform simulations for two different cases of idealised supercells using two double-moment bulk microphysics schemes and a bin microphysics scheme. The simulations cover a comprehensive range of values for cloud droplet number concentration (CDNC) and cloud condensation nuclei (CCN) concentration as a proxy for aerosol effects on convective clouds. We have developed a new cloud tracking algorithm to analyse the morphology and time evolution of individually tracked convective cells in the simulations and their response to the aerosol perturbations. This analysis confirms an expected decrease in warm rain formation processes due to autoconversion and accretion for more polluted conditions. There is no evidence of a significant increase in the total amount of latent heat, as changes to the individual components of the integrated latent heating in the cloud compensate each other. The latent heating from freezing and riming processes is shifted to a higher altitude in the cloud, but there is no significant change to the integrated latent heat from freezing. Different choices in the treatment of deposition and sublimation processes between the microphysics schemes lead to strong differences including feedbacks onto condensation and evaporation. These changes in the microphysical processes explain some of the response in cloud mass and the altitude of the cloud centre of gravity. However, there remain some contrasts in the development of the bulk cloud parameters between the microphysics schemes and the two simulated cases.

Sensitivity study of the planetary boundary layer and microphysical schemes to the initialization of convection over the Arabian Peninsula

“…(c) Zoominto the UAE with the surface stations from NCM (red dots) and GTS (white dots) used for validation. The black and blue dots denotes the locations for the time series shown in section rain due to nonlinear effects(Khain et al 2009;Heikenfeld et al 2019).…”

Explicit aerosol–cloud interactions in the Dutch Atmospheric Large-Eddy Simulation model DALES4.1-M7

“…The implementation of an explicit aerosol framework is a step forward in the simulation of aerosol-cloud interactions in the DALES model (Heus et al, 2010;Ouwersloot et al, 2017) as we can now quantify the feedback of the cloud microphysics on the aerosol population. Moreover, the aerosol module M7 (Vignati et al, 2004) represents an external mixture of multiple aerosol species.…”

“…For more information and details on the implementation of this scheme in DALES, see Sect. 2.8 of Heus et al (2010).…”

“…The model used in this study is the Dutch Atmospheric Large-Eddy Simulation (DALES) (Heus et al, 2010;Ouwersloot et al, 2017), version 4.1. DALES was initially designed to study the physics of the atmospheric boundary layer.…”

Near-global-scale high-resolution seasonal simulations with WRF-Noah-MP v.3.8.1

“…The reasons to choose this particular region are manifold: (1) the main focus of our work is on tropical convection, (2) applying the WRF model in polar regions requires a special set-up of the physical parameterizations (Bromwich et al, 2018;Hines and Bromwich, 2017), and (3) the applied regular latitude-longitude grid leads to very high mapscale factors beyond 65 • latitude, thus enforcing a very short model integration time step.…”