Modelling tracer transport by a cumulus ensemble: lateral boundary conditions and large-scale ascent

[摘要] The vertical transport of tracers by a cumulus ensemble at the TOGA-COAREsite is modelled during a 7 day episode using 2-D and 3-D cloud-resolvingsetups of the Weather Research and Forecast (WRF) model. Lateral boundaryconditions (LBC) for tracers, water vapour, and wind are specified and thehorizontal advection of trace gases across the lateral domain boundaries isconsidered.Furthermore, the vertical advection oftrace gases by the large-scale motion (short: vertical large-scale advectionof tracers, VLSAT) is considered. It is shown that including VLSAT partiallycompensates the calculated net downward transport from the middle and uppertroposphere (UT) due to the mass balancing mesoscale subsidence induced bydeep convection. Depending on whether the VLSAT term is added or not,modelled domain averaged vertical tracer profiles can differ significantly.Differences between a 2-D and a 3-D model run weremainly attributed to an increase in horizontal advection across the lateraldomain boundaries due to the meridional wind component not considered in the2-D setup.

[学科分类] 大气科学