Weibull-k Revisited: “Tall” Profiles and Height Variation of Wind Statistics

The Weibull distribution is commonly used to describe climatological wind-speed distributions in the atmospheric boundary layer. While vertical profiles of mean wind speed in the atmospheric boundary layer have received significant attention, the variation of the shape of the wind distribution with height is less understood. Previously we derived a probabilistic model based on similarity theory for calculating the effects of stability and planetary boundary-layer depth upon long-term mean wind profiles. However, some applications (e.g. wind energy estimation) require the Weibull shape parameter (k), as well as mean wind speed. Towards the aim of improving predictions of the Weibull- \(k\) profile, we develop expressions for the profile of long-term variance of wind speed, including a method extending our probabilistic wind-profile theory; together these two profiles lead to a profile of Weibull-shape parameter. Further, an alternate model for the vertical profile of Weibull shape parameter is made, improving upon a basis set forth by Wieringa (Boundary-Layer Meteorol, 1989, Vol. 47, 85–110), and connecting with a newly-corrected corollary of the perturbed geostrophic-drag theory of Troen and Petersen (European Wind Atlas, 1989, Risø National Laboratory, Roskilde). Comparing the models for Weibull-k profiles, a new interpretation and explanation is given for the vertical variation of the shape of wind-speed distributions. Results of the modelling are shown for a number of sites, with a discussion of the models’ efficacy and applicability. The latter includes a comparative evaluation of Wieringa-type empirical models and perturbed-geostrophic forms with regard to surface-layer behaviour, as well as for heights where climatological wind-speed variability is not dominated by surface effects.     

Innovating the IPCC review process—the potential of young talent

There is significant potential in young talent for enhancing the credibility of the scientific assessments such as the IPCC’s by contributing to quality assurance and quality control. In this essay, we reflect on an experiment that was done by the Dutch government as part of its government review of a contribution to the IPCC’s Fifth Assessment Report (AR5). In an effort to review the entire Working Group II contribution to the AR5 within the official review period for the Second Order Draft (SOD), the PBL Netherlands Environmental Assessment Agency turned to PhD students. This article shows that a systematic review focusing on transparency and errors of a large scientific assessment document using young talented scientists can be successful if certain conditions are met. The reviewers need to have intrinsic motivation to conduct the review. There needs to be a communication plan that fosters engagement and a clear methodology to guide the reviewers through their task. Based on this experiment in review, we reflect on the wider potential for openness and crowdsourcing in scientific assessment processes such as the IPCC’s.     

Early Last Interglacial Greenland Ice Sheet melting and a sustained period of meridional overturning weakening: a model analysis of the uncertainties

Proxy-data suggest that the Last Interglacial (LIG; ~130–116 ka BP) climate was characterized by higher temperatures, a partially melted Greenland Ice Sheet (GIS) and a changed Atlantic meridional overturning circulation (AMOC). Notwithstanding the uncertainties in LIG palaeoclimatic reconstructions, this setting potentially provides an opportunity to evaluate the relation between GIS melt and the AMOC as simulated by climate models. However, first we need to assess the extent to which a causal relation between early LIG GIS melt and the weakened AMOC is plausible. With a series of transient LIG climate simulations with the LOVECLIM earth system model, we quantify the importance of the major known uncertainties involved in early LIG GIS melt scenarios. Based on this we construct a specific scenario that is within the parameter space of uncertainties and show that it is physically consistent that early LIG GIS melting kept the AMOC weakened. Notwithstanding, this scenario is at the extreme end of the parameter space. Assuming that proxy-based reconstructions of early LIG AMOC weakening offer a realistic representation of its past state, this indicates that either (1) the AMOC weakening was caused by other forcings than early LIG GIS melt or (2) the early LIG AMOC was less stable than indicated by our simulations and a small amount of GIS melt was sufficient to keep the AMOC in the weak state of a bi-stable regime. We argue that more intensive research is required because of the high potential of the early LIG to evaluate model performance in relation to the AMOC response to GIS melt.     

A double slip non-coaxial flow rule for viscous-plastic Cosserat materials

We propose a double slip non-coaxial plastic model within the framework of a Cosserat continuum theory. In a Cosserat continuum, a material point possesses the degrees of freedom of an infinitesimal rigid body: two translations and one rotation in 2D. We formulate the plastic model into viscous-plastic constitutive relationships and illustrate the viscous-plastic behaviour of the model by means of numerical solution of a simple shear problem.     

Hydrologic Variability and Its Control of Phytoplankton Community Structure and Function in Two Shallow,Coastal, Lagoonal Ecosystems: The Neuse and New River Estuaries,North Carolina,USA

Hydrologic conditions, especially changes in freshwater input, play an important, and at times dominant, role in determining the structure and function of phytoplankton communities and resultant water quality of estuaries. This is particularly true for microtidal, shallow water, lagoonal estuaries, where water flushing and residence times show large variations in response to changes in freshwater inputs. In coastal North Carolina, there has been an increase in frequency and intensity of extreme climatic (hydrologic) events over the past 15 years, including eight hurricanes, six tropical storms, and several record droughts; these events are forecast to continue in the foreseeable future. Each of the past storms exhibited unique hydrologic and nutrient loading scenarios for two representative and proximate coastal plain lagoonal estuaries, the Neuse and New River estuaries. In this synthesis, we used a 13-year (1998–2011) data set from the Neuse River Estuary, and more recent 4-year (2007–2011) data set from the nearby New River Estuary to examine the effects of these hydrologic events on phytoplankton community biomass and composition. We focused on the ability of specific taxonomic groups to optimize growth under hydrologically variable conditions, including seasonal wet/dry periods, episodic storms, and droughts. Changes in phytoplankton community composition and biomass were strongly modulated by the amounts, duration, and seasonality of freshwater discharge. In both estuaries, phytoplankton total and specific taxonomic group biomass exhibited a distinctive unimodal response to varying flushing rates resulting from both event-scale (i.e., major storms, hurricanes) and more chronic seasonal changes in freshwater input. However, unlike the net negative growth seen at long flushing times for nano-/microphytoplankton, the pigments specific to picophytoplankton (zeaxanthin) still showed positive net growth due to their competitive advantage under nutrient-limited conditions. Along with considerations of seasonality (temperature regimes), these relationships can be used to predict relative changes in phytoplankton community composition in response to hydrologic events and changes therein. Freshwater inputs and droughts, while not manageable in the short term, must be incorporated in water quality management strategies for these and other estuarine and coastal ecosystems faced with increasing frequencies and intensities of tropical cyclones, flooding, and droughts.     

Zur experimentellen Tektonik

Ohne ZusammenfassungI. Cbl. f. Min. usw., Abt. B, 1928, 609; II. Natur und Museum, 1929, 225; III. Natur und Museum, 1930, 258; IV. Die Naturwissenschaften, 1930, 741.     

Tektonische Probleme am Nordrand des Harzes

Ohne ZusammenfassungVgl.Cloos, Eine neue Störungsform, (8).     

Der geologische Lehrstuhl an der Universität Neuenburg in der Schweiz

Ohne Zusammenfassung