The 1-way on-line coupled atmospheric chemistry model system MECO(n) – Part 2: On-line coupling with the Multi-Model-Driver (MMD)

摘要

A new, highly flexible model system for the seamless dynamicaldown-scaling of meteorological and chemical processes from the globalto the meso-γ scale is presented. A global model and a cascadeof an arbitrary number of limited-area model instances runconcurrently in the same parallel environment, in which the coarsergrained instances provide the boundary data for the finer grainedinstances. Thus, disk-space intensive and time consuming intermediateand pre-processing steps are entirely avoided and the timeinterpolation errors of common off-line nesting approaches areminimised. More specifically, the regional model COSMO of the GermanWeather Service (DWD) is nested on-line into the atmosphericgeneral circulation model ECHAM5 within the Modular Earth SubmodelSystem (MESSy) framework. ECHAM5 and COSMO have previously beenequipped with the MESSy infrastructure, implying that the same processformulations (MESSy submodels) are available for both models. Thisguarantees the highest degree of achievable consistency, between both,the meteorological and chemical conditions at the domain boundaries ofthe nested limited-area model, and between the process formulations onall scales.The on-line nesting of the different models is established bya client-server approach with the newly developed Multi-Model-Driver(MMD), an additional component of the MESSy infrastructure. With MMDan arbitrary number of model instances can be run concurrently withinthe same message passing interface (MPI) environment, the respectivecoarser model (either global or regional) is the server for the nestedfiner (regional) client model, i.e. it provides the data required tocalculate the initial and boundary fields to the client model.On-line nesting means that the coupled (client-server) models exchangetheir data via the computer memory, in contrast to the data exchangevia files on disk in common off-line nesting approaches. MMD consistsof a library (Fortran95 and some parts in C) which is based on the MPIstandard and two new MESSy submodels, MMDSERV and MMDCLNT (bothFortran95) for the server and client models, respectively.MMDCLNT contains a further sub-submodel, INT2COSMO, for theinterpolation of the coarse grid data provided by the server models(either ECHAM5/MESSy or COSMO/MESSy) to the grid of the respectiveclient model (COSMO/MESSy). INT2COSMO is based on the off-linepre-processing tool INT2LM provided by the DWD.The new achievements allow the setup of model cascades for zooming(down-scaling) from the global scale to the lower edge of themeso-γ scale (≈1 km) with a very high degree ofconsistency between the different models and between the chemical andmeteorological boundary conditions.