A highly modular and scale-consistent Terrestrial Systems Modeling Platform (TerrSysMP) is presented. The modeling platform consists of an atmospheric model (Consortium for Small-Scale Modeling; COSMO), a land surface model (the NCAR Community Land Model, version 3.5; CLM3.5), and a 3D variably saturated groundwater flow model (ParFlow). An external coupler (Ocean Atmosphere Sea Ice Soil, version 3.0; OASIS3) with multiple executable approaches is employed to couple the three independently developed component models, which intrinsically allows for a separation of temporal-spatial modeling scales and the coupling frequencies between the component models.Idealized TerrSysMP simulations are presented, which focus on the interaction of key hydrologic processes, like runoff production (excess rainfall and saturation) at different hydrological modeling scales and the drawdown of the water table through groundwater pumping, with processes in the atmospheric boundary layer. The results show a strong linkage between integrated surface-groundwater dynamics, biogeophysical processes, and boundary layer evolution. The use of the mosaic approach for the hydrological component model (to resolve subgrid-scale topography) impacts simulated runoff production, soil moisture redistribution, and boundary layer evolution, which demonstrates the importance of hydrological modeling scales and thus the advantages of the coupling approach used in this study.Real data simulations were carried out with TerrSysMP over the Rur catchment in Germany. The inclusion of the integrated surface-groundwater flow model results in systematic patterns in the root zone soil moisture, which influence exchange flux distributions and the ensuing atmospheric boundary layer development. In a first comparison to observations, the 3D model compared to the 1D model shows slightly improved predictions of surface fluxes and a strong sensitivity to the initial soil moisture content.

BACKGROUND. State predictions for terrestrial systems are usually performed by means of numerical process models, which consider all compartments. However, it is unclear to what extent system heterogeneity must be considered for a particular set of conditions and for different types of model predictions.Numerical process models of the terrestrial system usually consider three vertically stacked mediarepresenting the subsurface, including ground and surface water; vegetation; and atmosphere-that are typically coded in three separate compartment models. These compartment models interact at their

In 2011, the German Federal Ministry of Transport, Building and Urban Development laid the foundation of the Hans-Ertel Centre for Weather Research [Hans-Ertel-Zentrum für Wetterforschung (HErZ)] in order to better connect fundamental meteorological research and teaching at German universities and atmospheric research centers with the needs of the German national weather service Deutscher Wetterdienst (DWD). The concept for HErZ was developed by DWD and its scientific advisory board with input from the entire German meteorological community. It foresees core research funding of about €2,000,000 yr−1 over a 12-yr period, during which time permanent research groups must be established and DWD subjects strengthened in the university curriculum. Five priority research areas were identified: atmospheric dynamics and predictability, data assimilation, model development, climate monitoring and diagnostics, and the optimal use of information from weather forecasting and climate monitoring for the benefit of society. Following an open call, five groups were selected for funding for the first 4-yr phase by an international review panel. A dual project leadership with one leader employed by the academic institute and the other by DWD ensures that research and teaching in HErZ is attuned to DWD needs and priorities, fosters a close collaboration with DWD, and facilitates the transfer of fundamental research into operations. In this article, we describe the rationale behind HErZ and the road to its establishment, present some scientific highlights from the initial five research groups, and discuss the merits and future development of this new concept to better link academic research with the needs and challenges of a national weather service.

Fog in complex terrain shows large temporal and spatial variations that can only be simulated with a three-dimensional model, but more modifications than simply increasing the resolution are needed. For a better representation of fog, we present a second-moment cloud water scheme with a parametrization of the Köhler theory which is combined with the mixed-phase Ferrier microphysics scheme. The more detailed PAFOG microphysics produce many differences to the first-moment Ferrier scheme and are responsible for the typically low liquid water content of fog. The inclusion of droplet sedimentation in the Ferrier scheme cannot reproduce the results obtained with PAFOG, as there is a large sensitivity to the sedimentation velocity. With explicitly predicted droplet number concentrations, sedimentation of cloud water can be modelled with variable fall speeds, which mainly affects the vertical distribution of cloud water and the end of the fog's life cycle. The complex topography of the Swiss Alps and their surroundings are used for model testing. As the focus is on the model's ability to forecast the spatial distribution of fog, cloud patterns derived from high-resolution MSG satellite data, rather than few point observations from ground stations, are used. In a five-day period of anticyclonic conditions, the satellite-observed fog patterns showed large day-to-day variations from almost no fog to large areas of fog. This variability was very well predicted in the three-dimensional fog forecast. Furthermore, the second-moment cloud water scheme shows a better agreement with the satellite observations than its firstmoment counterpart. For model initialization, the complex topography is actually a simplifying factor, as cold air flow and pooling dominate the more uncertain processes of evapotranspiration or errors in the soil moisture field.

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