The Physics of Heat Waves: What Causes Extremely High Summertime Temperatures?

We analyze observations and develop a hierarchy of models to understand heat waves – long-lived, high temperature anomalies – and extremely high daily temperatures during summertime in the continental extratropics. Throughout the extratropics, the number of extremely hot days found in the three hottest months is much greater than expected from a random, single-process model. Furthermore, in many locations the temperature skewness switches from negative on daily timescales to positive on monthly timescales (or shifts from positive on daily timescales to higher positive values on monthly timescales) in ways that cannot be explained by averaging alone. These observations motivate a hierarchy of models of the surface energy and moisture budgets that we use to illuminate the physics responsible for daily and monthly averaged temperature variability. Shortwave radiation fluctuations drive much of the variance and the negative skewness found in daily temperature observations. On longer timescales, precipitation-induced soil moisture anomalies are important for temperature variability and account for the shift toward positive skewness in monthly averaged temperature. Our results demonstrate that long-lived heat waves are due to (i) the residence time of soil moisture anomalies and (ii) a nonlinear feedback between temperature and evapotranspiration via the impact of temperature on vapor pressure deficit. For most climates, these two processes give rise to infrequent, long-lived heat waves in response to randomly distributed precipitation forcing. Combined with our results concerning high-frequency variability, extremely hot days are seen to be state-independent filigree driven by shortwave variability acting on top of longer-lived, moisture driven heat waves.

On the Hierarchy of Models for Pipe Transients: From Quasi-2D Water Hammer Models to Full 3D CFD Models

A hierarchy of models exists in the literature for the simulation of pipe transients. One-dimensional water hammer models are readily available and provide a cost-effective tool for the analysis of such transients. The main shortcoming of 1D models is the quasi-steady approximation of the frictional term, which results in poor modelling of the attenuation of the transient. To overcome this drawback, quasi-2D water hammer models were introduced, which allow the computation of the unsteady velocity profile and hence provide improved modelling of the attenuation phenomenon. Recently, interest has developed in the use of CFD models based on the Navier-Stokes equations in the simulation of fluid transients. Both axisymmetric CFD models and full 3D CFD models are used in this regard. The aim of the current paper is to carry out a comparative study between the performance of quasi-2D water hammer models, axisymmetric CFD models and full 3D CFD models. Numerical computations using the three models are performed for both laminar and turbulent flow cases. Present results show that the quasi-2D water hammer model and the axisymmetric CFD model provide near identical results in terms of computing the magnitude, phase and attenuation of the transient. Reported results also demonstrate the computational efficiency of the quasi-2D model, which provides results that agree reasonably well with the full 3D CFD model results while using a grid density which is an order of magnitude lower than the grid requirements for the full 3D CFD model.

Economic modeling of innovation ecosystems

Within the framework of traditional economic approaches that incline the researcher's attention to the ordering of systems, it is difficult to track and adequately assess the turbulent changes in the environment in the conditions of transformation of almost all spheres of the economy. The way out of this cognitive trap is possible in applying the tools of the ecosystem approach, which considers economic relations within a set of ecosystems as extra-organizational, self-organized forms of conducting commercial and social (non-commercial) entrepreneurship. A hierarchy of models of innovative ecosystems is proposed for scientific and practical analysis of the phenomenon under consideration and for developing recommendations for the formation of necessary conditions for the development of ecosystem relations. The combinatorics of environmental factors and internal structure allows us to construct a significant set of ecosystem models.

Predicting dielectric constants of pure liquids: fragment-based Kirkwood–Fröhlich model applicable over a wide range of polarity

A hierarchy of models yields reliable predictions for dielectric constants of liquids.