Abstract
Abstract. A modified cumulus convection parametrisation scheme is presented. This scheme computes the mass of air transported upward in a cumulus cell using conservation of moisture and a detailed distribution of convective precipitation provided by a reanalysis dataset. The representation of vertical transport within the scheme includes entrainment and detrainment processes in convective updrafts and downdrafts. Output from the proposed parametrisation scheme is employed in the National Institute for Environmental Studies (NIES) global chemical transport model driven by JRA-25/JCDAS reanalysis. The simulated convective precipitation rate and mass fluxes are compared with observations and reanalysis data. A simulation of the short-lived tracer 222Rn is used to further evaluate the performance of the cumulus convection scheme. Simulated distributions of 222Rn are evaluated against observations at the surface and in the free troposphere, and compared with output from models that participated in the TransCom-CH4 Transport Model Intercomparison. From this comparison, we demonstrate that the proposed convective scheme in general is consistent with observed and modeled results.
Highlights
Deep cumulus convection (DCC) plays an important role in the hydrological cycle of the climate system, the dynamics of the atmospheric circulation and the transport of trace gases within the troposphere
All meteorological data used in the National Institute for Environmental Studies (NIES) TM simulations discussed in this paper are provided by a reanalysis dataset produced by the Japan Meteorological Agency (JMA) and the Central Research Institute of Electric Power Industry (CRIEPI)
The JRA-25/JMA Climate Data Assimilation System (JCDAS) convective precipitation data is evaluated by comparing it with monthly mean data from the global Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) and special product data from the Modern Era Retrospective-analysis for Research and Applications (MERRA)
Summary
Deep cumulus convection (DCC) plays an important role in the hydrological cycle of the climate system, the dynamics of the atmospheric circulation and the transport of trace gases within the troposphere. Deep convective updrafts extend from the surface to the upper troposphere, with typical vertical velocities of several meters per second. After rapid ascent from the surface layer in DCC, tracers can be advected over long distances by the strong zonal winds that prevail in the upper troposphere (Allen et al, 1996; Zaucker et al, 1996). This relationship illustrates the important role that convection plays in long-range tracer transport. Along with largescale advection and vertical diffusion, cumulus convection is one of the most important transport processes affecting atmospheric tracers
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