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Thermally driven winds observed in complex terrain are characterized by a daily cycle dominated by two main phases: a diurnal phase in which winds blow upslope (anabatic), and a nocturnal one in which they revert their direction and blow downslope (katabatic). This alternating pattern also implies two transition phases, following sunrise and sunset respectively. Here we study the upslope component of the slope wind with a focus on the morning transition from the katabatic to the anabatic flow based on data from the MATERHORN experiment, performed in Salt Lake Desert (Utah) between Fall 2012 and Spring 2013 (Fernando et al, 2015). First of all, a criterion for the selection of purely thermally driven slope wind days is proposed and adopted to select five case studies, taken from both the spring and the autumn periods. Then, the analysis allowed the investigation of the driving mechanisms through the connection with the patterns of erosion of the nocturnal inversion in the valley bed at the foot of the slope under analysis. Three main patterns of erosion of the inversion in the particular topography of a gentle and isolated slope are identified: a) erosion due to upward growth of a convective boundary layer, b) erosion due to descent of the inversion top, and c) erosion due to a mix of the two previous mechanisms. The three patterns are then linked to the initiation of the transition by two different and competing mechanisms: mixing from above (top-down dilution) and surface heating from below. Finally, an analytical model for the description of slope circulation (Zardi and Serafin, 2015) has been used to diagnose the time of the transition.Zardi, D. and S. Serafin, 2015: An analytic solution for daily-periodic thermally-driven slope flow. Quart. J. Roy. Meteor. Soc., 141, 1968–1974. Fernando, H. J. S., Pardyjak, E. R., Di Sabatino, S., Chow, F. K., De Wekker, S. F. J., Hoch, S. W, Zsedrovits, T., 2015, The MATERHORN: Unraveling the intricacies of mountain weather. Bulletin Of The American Meteorological Society, 96, 1945-1967.

The presence of waves in the nocturnal boundary layer has proven to generate complex interaction with turbulence. On complex terrain environments, where turbulence is observed in a weak but continuous state of activity, waves can be a vehicle of additional production/loss of turbulence energy. The common approach based on the Reynolds decomposition is unable to disaggregate turbulence and wave motion, thus revealing impaired to explicit the terms of this additional interaction. In the current investigation, we adopt a triple-decomposition approach to separate mean, wave, and turbulence motions within near-surface boundary-layer flows, with the aim of unveiling the role of wave motion as source and/or sink of turbulence kinetic and potential energies in the respective explicit budgets. This investigation reveals that the waves contribute to the kinetic energy budget where the production is not shear-dominated and the budget equation does not reduce to a shear-dissipation balance (e.g., as it occurs close to a surface). Away from the surface, the buoyancy effects associated with the wave motion become a significant factor in generating a three-terms balance (shear-buoyancy-dissipation). Similar effects can be found in the potential energy budget, as the waves affect for instance the production associated with the vertical heat flux. On this basis, we develop a simple interpretation paradigm to distinguish two layers, namely near-ground and far-ground sublayer, estimating where the turbulence kinetic energy can significantly feed or be fed by the wave. To prove this paradigm and evaluate the explicit contributions of the wave motion on the turbulence kinetic and potential energies, we investigate a nocturnal valley flow observed under weak synoptic forcing in the Dugway Valley (Utah) during the MATERHORN Program. From this dataset, the explicit kinetic and potential energy budgets are calculated, relying on a variance-covariance analysis to further comprehend the balance of energy production/loss in each sublayer. With this investigation, we propose a simple interpretation scheme to capture and interpret the extent of the complex interaction between waves and turbulence in nocturnal stable boundary layers.

Low-level jets (LLJs) are a peculiar feature of the nocturnal Planetary Boundary Layer (PBL) and they have been extensively observed both in flat and complex terrain configurations. On the contrary, double-nosed LLJs have been rarely investigated. They essentially consist in the simultaneous occurrence of two noses (i.e. two wind-speed maxima) within the PBL vertical profile of wind speed, but their origin and mechanisms remain rather unclear.Data collected in an open valley during the MATERHORN field experiment are used here first to demonstrate that double-nosed LLJs are frequently observed at the site during stable nocturnal conditions, and second to describe the mechanisms that drive their formation. Structural characteristics of these double-nosed LLJs are originally described using refined criteria proposed in the literature.Two driving mechanisms for double-nosed LLJs are newly proposed in the current study. The first mechanism is wind-driven, in which the two noses are associated with different air masses flowing one on top of the other. The second mechanism is wave-driven, in which a flow perturbation generates an inertial-gravity wave. This wave vertically transports momentum causing the occurrence of a secondary nose, leading to the formation of a double-nosed LLJ. Careful examination of the temporal evolution of these events also revealed the short-lived and transitional nature of the secondary nose in both the mechanisms, as opposite to the primary nose whose evolution appeared instead driven by inertial oscillations. Application of two analytical inertial-oscillation models retrieved from the literature confirms this hypothesis. Indeed, both models satisfactorily reproduce the observed single-nosed LLJs but fail to capture the temporary formation of the secondary nose.

As part of H2020 OPERANDUM project, a multi-dimensional, open and user-friendly platform is being developed, named OPERANDUM Geospatial Information Knowledge Platform (GeoIKP), which enables stakeholders and end-users to improve their knowledge of nature-based solutions (NBS) as a long-term and sustainable measure for mitigation and reduction of flooding, coastal erosion, landslide and other hydro-meteorological hazards. This contribution offers an overview of GeoIKP and discusses in detail some of the innovative aspects of the platform, such as a the integration of a NBS data management portal with a web application offering advanced webGIS tools, a comprehensive catalogue of NBS, as well as analytical algorithms to demonstrate the effectiveness of NBS in reducing hydro-meteorological risks.The platform design is being based on intuitive techniques, ease of access, dynamic navigability, interactive knowledge management, and multiple format compatibility. It empowers the multiple and diverse actors involved in the NBS co-design/co-development process (policymakers, citizens, enterprises, scientists, etc.) to visualize and query geo-referenced data for the specific area of interest.In its first - yet preliminary - release, GeoIKP already offers a variety of functionalities and geo-referenced data of relevance for NBS, while at the same time it provides more standardized ways for NBS data (and metadata) management and cataloging. We conclude by reflecting on some of the current challenges associated with NBS data, such as adequacy and discoverability.

During the past decades, risk assessment experienced increasing interest in social science but also natural science and other disciplines. At the same time, risk reduction and mitigation gained in interest from local to global level due to the shift from reactive to proactive management. Hazard and risk assessment have been approached on different levels, nonetheless, they are lacking elements such as cross-border assessment or the integration of an ecological risk assessment. One of the objectives of the H2020 Operandum project is to provide an automated science-based assessment of risk for the social-ecological system and further of the applicability and performance of Nature-based Solutions (NBS) for risk mitigation of hydro-meteorological hazards.Within this project, an interactive webGIS analytical engine and an NBS catalogue are being developed as part of the Geospatial Information Knowledge Platform (GeoIKP). The analytical engine will encompass open Europe-wide hazard maps and link them with local high-resolution information from public and innovative data sources (e.g. Facebook). These two geo-tools are combined into a recommendation engine - NBS toolkit - trained on existing NBS. Using a holistic approach, the NBS toolkit aims at providing risk assessment and advanced recommendations on NBS usage for mitigation. For this approach, the NBS toolkit incorporates hazard and risk assessment in space and time, cost-benefit analysis, and additionally main drivers and constraints for NBS implementations as well as their geographical transferability, replicability and performance/effectiveness. This contribution will offer an insight into the concept and development of the NBS toolkit. Primarily, it will focus on the added value of the NBS toolkit for future nature-based implementation, risk mitigation management and decision-making at all levels. Challenges and current limitations of real-time risk assessment will also be discussed, with a focus on their implications on NBS monitoring and effectiveness.