Role of land surface processes and diffuse/direct radiation partitioning in simulating the European climate

[摘要] The influence of land processes and in particular of diffuse/direct radiationpartitioning on surface fluxes and associated regional-scale climate feedbacksis investigated using ERA-40 driven simulations over Europe performed with theCOSMO-CLM² Regional Climate Model (RCM). Two alternative Land SurfaceModels (LSMs), a 2nd generation LSM (TERRA_ML) and a more advanced3rd generation LSM (Community Land Model version 3.5), and two versionsof the atmospheric component are tested, as well as a revised couplingprocedure allowing for variations in diffuse/direct light partitioning at thesurface, and their accounting by the land surface component.

Overall, the RCM performance for various variables (e.g., surface fluxes,temperature and precipitation) is improved when using the more advanced3rd generation LSM. These improvements are of the same order of magnitudeas those arising from a new version of the atmospheric component,demonstrating the benefit of using a realistic representation of land surfaceprocesses for regional climate simulations. Taking into account the variability indiffuse/direct light partitioning at the surface further improves the modelperformance in terms of summer temperature variability at the monthly anddaily time scales. Comparisons with observations show that the RCMrealistically captures temporal variations in diffuse/direct lightpartitioning as well as the evapotranspiration sensitivity to thesevariations. Our results suggest that a modest but consistent fraction (up to3 %) of the overall variability in summer temperature can be explained byvariations in the diffuse to direct ratio.

[学科分类] 地球化学与岩石