Representation of transport and scavenging of trace particlesin the Emanuel moist convection scheme

Abstract

In the Tropics, cumulus convection has a major influence on precipitation and vertical transport of atmospheric particles, which are subject to scavenging by precipitation. A new parametrization of transport and scavenging of trace particles by convective clouds and precipitation has been developed and introduced in the Laboratoire de Météorologie Dynamique general circulation model (LMDz). This model uses the deep convection scheme of Emanuel, which is particularly suited for the Tropics. Our parametrization of transport and scavenging is closely linked to this scheme and our developments follow step-by-step the building of this convection representation. The purpose of this study is to understand better the influence of convection on the tracer vertical distribution and to assess the role of the convection parametrization.Short-term and long-term simulations have been performed focusing on the concentrations of the natural radionuclide 7 Be, which is produced mainly in the stratosphere and upper troposphere and attaches to available aerosols. Single-column simulations forced by data from the Tropical Ocean-Global Atmosphere-Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE) show the high efficiency of in-cloud scavenging by convective and large-scale processes in the removal of the tracer. These simulations show that, in the LMDz model, convection does not affect radionuclide concentrations as much as stratiform clouds and associated precipitation. In the free troposphere and in the boundary layer, below-cloud evaporation of rain has a major effect on tracer distribution, unlike impaction, which has a negligible effect. Three-dimensional model simulation results are compared with surface data of a station belonging to the worldwide network of the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO). We show that this new parametrization is able to reproduce the observed yearly averaged concentrations of 7 Be at the surface and decrease by a third the overestimation of radionuclides formerly simulated without convective scavenging. LMDz simulations have been also performed over the year 2007 on a global scale using the terragenic 210 Pb and cosmogenic 7 Be radionuclides.

Subregional inversion of North African dust sources

“…After emission, fine mode dust is included in the fine mode aerosols tracer (which also includes black carbon, particulate organic matter, and sulfate aerosols), so in practice the SPLA model has only five tracers now. Additional work has been done to update the SPLA model according to the latest developments of the LMDz model, including the parameterization of thermals in the boundary layer [ Hourdin et al , ] and the convective transport and scavenging scheme [ Pilon et al , ].…”

Toward High‐Resolution Global Atmospheric Inverse Modeling Using Graphics Accelerators

“…It is completed by a thermal model, formulated in terms of mass fluxes, for the case of convective boundary layers (Rio & Hourdin, 2008). Transport by deep convection is derived from the Emanuel (1991) scheme (see, e.g., Pilon et al., 2015, and references therein), which, in practice, links all vertical levels between the cloud base and the level of neutral buoyancy together in a convective system. This link makes the data volume of convective mass fluxes quadratically dependent on the number of vertical levels of the model.…”

Seasonal Behavior of Aerosol Vertical Concentration in Dakar and Role Played by the Sea-Breeze

“…In addition to these latter thermodynamical features, the rainfall can play an important role in the vertical distribution of aerosols over West Africa. The aerosols suspended can be scavenging by convective and stratiform precipitation [41].…”