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


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Representation of transport and scavenging of trace particlesin the Emanuel moist convection scheme
Q.J.R. Meteorol. Soc.
Romain Pilon
Jean-Yves Grandpeix, Philippe Heinrich
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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 M´et´eorologie
Dynamique general circulation model (LMDz).Thismodel 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 7Be,which is producedmainly in the stratosphere
and upper troposphere and attaches to available aerosols. Single-column simulations
forced by data fromthe TropicalOcean–GlobalAtmosphere–CoupledOcean–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-dimensionalmodel 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 7Be 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 210Pb and cosmogenic 7Be radionuclides.
parametrization, deep convection, scavenging, transport, radionuclide, climate model
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25/04/2022 9:31
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