Sensitivity of limited area atmospheric simulations to lateral boundary conditions in idealized experiments

  • The goal of limited area models (LAMs) is to downscale coarse-gridded general circulation model output to represent small-scale features of weather and climate. The LAM needs information from the driving coarse-gridded model passing through its lateral boundaries. The treatment of this information transfer causes inconsistencies between driving and nested models and, subsequently, issues in regional weather and climate simulations. This work examines errors arising from choices taken by the modeler (temporal update frequency of boundary data, spatial resolution jump, and numerical lateral boundary formulation) systematically in an idealized simulation environment. So-called Big-Brother Experiments were performed with the LAM COSMO-CLM (0.11° grid spacing). A baroclinic wave in a zonal channel was simulated over flat terrain with and without a Gaussian hill. The results reveal that the quality of the driving data, here represented by simulations only differing from the LAM simulations by reduced spatial resolution, dominates the performance of the nested model. Consequently, at the simulated mesoscale, the performance of the nested small-scale model simulations is weakly sensitive to the numerical lateral boundary formulation (Davies relaxation or the newly implemented, computationally less demanding Mesinger Eta-model formulation). The performance sensitivity to boundary update frequency and resolution jump is small when at least 6-hourly updates and a resolution jump factor of maximally six is used. Gaussian hill LAM simulations illustrated the strength of downscaling; they can represent small-scale features missing in the coarse-scale driving simulations. In the idealized simulation experiments, spectral nudging is not advisable as it imprints the driving models deficits on the nested simulation.
Author:Nora Leps, Jennifer Brauch, Bodo AhrensORCiDGND
Parent Title (English):Journal of advances in modeling earth systems
Place of publication:Fort Collins, Colo.
Document Type:Article
Date of Publication (online):2019/07/20
Date of first Publication:2019/07/20
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2022/03/22
Tag:COSMO-CLM; idealized big brother experiments; lateral boundary conditions
Page Number:14
First Page:2694
Last Page:2707
This work was carried out in the framework of the German research project MiKlip II: Regionalisation (FKZ 01LP1518C), funded by the German Federal Ministry of Education and Research (BMBF). COSMO-CLM is the community model of the German regional climate research, which is available for community members at the website ( Namelists for reproducing the simulations and the data used for evaluation is available online: (DOI 10.5281/zenodo.2671698).
Institutes:Geowissenschaften / Geographie
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 55 Geowissenschaften, Geologie / 550 Geowissenschaften
Licence (German):License LogoCreative Commons - Namensnennung-Nicht kommerziell - Keine Bearbeitung 4.0