Comparison of Measured and Numerically Simulated Turbulence Statistics in a Convective Boundary Layer Over Complex Terrain     

Raj K. Rai  Larry K. Berg  Branko Kosović  Jeffrey D. Mirocha  Mikhail S. Pekour  William J. Shaw 《Boundary-Layer Meteorology》2017,163(1):69-89

The Weather Research and Forecasting (WRF) model can be used to simulate atmospheric processes ranging from quasi-global to tens of m in scale. Here we employ large-eddy simulation (LES) using the WRF model, with the LES-domain nested within a mesoscale WRF model domain with grid spacing decreasing from 12.15 km (mesoscale) to 0.03 km (LES). We simulate real-world conditions in the convective planetary boundary layer over an area of complex terrain. The WRF-LES model results are evaluated against observations collected during the US Department of Energy-supported Columbia Basin Wind Energy Study. Comparison of the first- and second-order moments, turbulence spectrum, and probability density function of wind speed shows good agreement between the simulations and observations. One key result is to demonstrate that a systematic methodology needs to be applied to select the grid spacing and refinement ratio used between domains, to avoid having a grid resolution that falls in the grey zone and to minimize artefacts in the WRF-LES model solutions. Furthermore, the WRF-LES model variables show large variability in space and time caused by the complex topography in the LES domain. Analyses of WRF-LES model results show that the flow structures, such as roll vortices and convective cells, vary depending on both the location and time of day as well as the distance from the inflow boundaries.  相似文献   

Heinrich-type glacial surges in a low-order dynamical climate model     

Mikhail Verbitsky  Barry Saltzman 《Climate Dynamics》1994,10(1-2):39-48

Recent studies suggest the occurrence of sporadic episodes during which the ice streams that discharge ice sheets become enormously active, producing large numbers of icebergs (reflected in North Atlantic sea cores as Heinrich events) and possibly causing the partial collapse of the ice sheets. To simulate the mechanism of internal thermo-hydrodynamical instability implied by such behavior in the context of a more general paleoclimate dynamics model (PDM), we introduce a new sliding-catastrophe function that can account for ice-sheet surges. In particular, using simple scaling estimates derived from the equations of motion and thermo-conductivity for ice flow, we express this function in terms of the thickness, density, viscosity, heat-capacity, and heat-conductivity of ice. Analysis of the properties of this function suggests that these Heinrich-type instability events might be of three possible kinds: the first type of event occurs in periods of glacial maximum when temperature conditions on the ice surface are extremely cold, but internal friction within bottom boundary layer is also at its maximum and is strong enough to melt ice and cause its surge. The second type of event may happen during an interglacial, when the ice thickness is small but relatively warm climatic conditions on the upper surface of ice can be easily advected with the flow of ice to the bottom where even a small additional heating due to friction may cause melting. The third and, perhaps, most interesting type of event is one that may occur during ice sheet growth; in this period particles of ice reaching the bottom still remember the warm temperature conditions of the previous interglacial and additional heating due to increasing friction associated with the growing ice sheet may again cause melting. To the extent that the upper glacier surface temperature depends on atmospheric carbon dioxide concentration, this third case introduces the interesting possibility that earlier CO₂ concentrations may be as important for the present-day climate as its current value. We present results of numerical experiments demonstrating how these three kinds of instability can originate and interact with other components of the global climate system to produce variations of the Heinrich-event type. In particular, according to our model the climate system seems more vulnerable to surges during the penultimate interglacial period than in the present one, which may contribute to an explanation of the recent results of the Greenland Ice Core Project.  相似文献   

Effective two-phase flow through highly heterogeneous porous media: Capillary nonequilibrium effects   总被引：1，自引：0，他引：1  

Alain Bourgeat  Mikhail Panfilov 《Computational Geosciences》1998,2(3):191-215

We consider the two-phase flow through a dual-porosity medium, characterized by a period of heterogeneity ω, a ratio of global permeabilities ∈_K, and a ratio of the order of capillary forces ∈_c. The limit when ω tends to zero at different values of ∈_K and ∈_c gives four classes of global behavior, differing by the type of elementary flows at the one-cell level. We propose a diagram of their predominance. A macro-scale model is constructed by formal homogenization techniques for one of these classes; it shows a nonlinear kinetic relationship for the averaged capillary pressure functions, and leads to a decomposition for the effective phase permeability tensors. A capillary relaxation time is explicitly determined. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Vertical Distribution of Gelatinous Macroplankton in the North Pacific Observed by Manned Submersibles Mir-1 and Mir-2     

Mikhail E. Vinogradov  Elvira A. Shushkina 《Journal of Oceanography》2002,58(2):295-303

The vertical distribution of several medusa species in the Kurile-Kamtchatka region of the Pacific Ocean is described. Animals were observed in the light cone from deep-sea submersibles Mir-1 and Mir-2 throughout the water column, from the surface to 5000–6000 m at four different sites. Bathy- and abyssopelagic species are noted along with the species living in an extremely wide depth range. A faunistic border is revealed at a depth of 3000 m. The contribution of gelatinous animals (medusae, siphonophores, salps) to the total deep-sea plankton biomass was estimated using a wire reference cube during nine dives in the highly productive areas of the northwest Pacific, eastern Pacific (California, Costa-Rica Dome), and subtropical oligotrophic areas. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

The role of the Kazakhstan orocline in the late Paleozoic amalgamation of Eurasia   总被引：3，自引：0，他引：3  

Alexandra Abrajevitch  Rob Van der Voo  Mikhail L. Bazhenov  Natalia M. Levashova  Phil J.A. McCausland   《Tectonophysics》2008,455(1-4):61-76

After the 2005 Kashmir earthquake, we mapped surface ground fractures in Tangdhar, Uri, Rajouri and Punch sectors and liquefaction features in Jammu area lying close to the eastern side of the Line of Control (LOC) in Kashmir, India. The NW trending ground fractures occurred largely in the hanging wall zone of the southeastern extension of the causative fault in Tangdhar and Uri sectors. The principal compressive stress deduced from the earthquake induced ground fractures is oriented at N10°, whereas the causative Balakot–Bagh fault strikes 330°. The fault-plane solution indicates primarily SW thrusting of the causative fault with a component of strike–slip motion. The ground fractures reflect pronounced strike–slip together with some tensile component. The Tangdhar area showing left-lateral strike–slip motion lies on the hanging wall, and the Uri region showing right-lateral strike–slip movement is located towards the southeastern extension of the causative fault zone. The shear fractures are related to static stress that was responsible for the failure of causative fault. The tensile fractures with offsets are attributed to combination of both static and dynamic stresses, and the fractures and openings without offsets owe their origin due to dynamic stress. In Punch–Rajouri and Jammu area, which lies on the footwall, the fractures and liquefactions were generated by dynamic stress. The occurrence of liquefaction features in the out board part of the Himalayan range front near Jammu is suggestive of stress transfer  230 km southeast of the epicenter. The Balakot–Bagh Fault (BBF), the Muzaffarabad anticline, the rupture zone of causative fault and the zone of aftershocks — all are aligned in a  25 km wide belt along the NW–SE trending regional Himalayan strike of Kashmir region and lying between the MBT and the Riasi Thrust (Murree Thrust), suggesting a seismogenic zone that may propagate towards the southeast to trigger an earthquake in the eastern part of the Kashmir region.  相似文献   

The CO2-induced thickening/thinning of the Greenland and Antarctic ice sheets as simulated by a GCM (CCMI) and an ice-sheet model     

Mikhail Y Verbitsky  Robert J Oglesby 《Climate Dynamics》1995,11(4):247-253

Scaling analysis shows that the mean thickness of an ice sheet depends on the product of two poorly known quantities, the ice viscosity and the net snow accumulation rate. We adjust the viscosity of an ice sheet in order to get a consistent value of this product for the present-day ice sheet volume and area given the net snow accumulation rate calculated by an atmospheric general circulation model (GCM). We then hold this artificial rheology constant in further numerical experiments. We hope that in doing so we can partially compensate for systematic GCM errors in simulating the snow accumulation rate, and, therefore, thickening/thinning of ice sheets will depend mostly on the tendency in the net accumulation change rather than on its absolute value. Using this approach, the response of the Greenland and Antarctic ice sheets to doubling CO₂ concentration is simulated and the horizontal distribution of possible thickening/thinning of polar ice obtained. We find that, initially, the region of thickening ice is close to the area of increased snowfall rate, but later it significantly changes under the influence of internal ice flow dynamics. The sea-level changes predicted by our experiments agree with some empirical estimates. The sensitivity experiment with assigned basal sliding does not show significant changes in the large-scale ice topography, meaning, for example, that there is no indication of a possible disintegration of the West Antarctic ice sheet. At the same time, the regional thickening/thinning of ice (and consequently the sea-level change) depends strongly on processes at the ice sheet bottom.  相似文献   

Equilibrium ice sheet scaling in climate modeling     

Mikhail Ya Verbitsky 《Climate Dynamics》1992,7(2):105-110

A set of simple scaling formulas related to ice sheet evolution is derived from the dynamic and thermodynamic equations for ice and is used to consider two common situations: (a) when we wish to estimate potential ice sheet characteristics given the prescribed net snow accumulation over an area; and (b) when we wish to reconstruct net snow accumulation and vertical temperature difference within the ice sheet given empirical data only concerning ice sheet area and volume. The scaling formulas are applied to the present day Antarctic and Greenland ice sheets, as well as to some ancient ice sheets, and are used to estimate the potential global sea level change due to greenhouse warming.  相似文献   

Modeling the dynamics of the land-sea breeze circulation for air quality modeling   总被引：1，自引：0，他引：1  

Mikhail Novitsky  Danny D. Reible  Bernardo M. Corripio 《Boundary-Layer Meteorology》1992,59(1-2):163-175

Conventional atmospheric dispersion and air quality models require that the wind field be known with a higher resolution than is currently available from field monitoring stations in most coastal areas. In this paper, a numerical model is developed to predict the wind flow field during the land-sea breeze. The form and assumptions and method of solution of the model are described. The model output is compared to atmospheric data taken from a field study conducted in the Santa Barbara Channel and Ventura-Oxnard plain in southern California.  相似文献   

Asthenospheric ice-load effects in a global dynamical-system model of the Pleistocene climate     

Barry Saltzman  Mikhail Ya Verbitsky 《Climate Dynamics》1992,8(1):1-11

In a previous dynamical model the late Cenozoic climate variations were simulated, taking into account free and forced variations of atmospheric carbon dioxide acting in concert with changes in global ice mass and the deep ocean thermal state, all under the influence of the known earth-orbital radiative changes. This model is now extended by adding another relevant variable, bedrock/asthenosphere depression, including its associated ice-calving effects. Within the context of this extended model we (1) demonstrate the main results of previous bedrock/ice sheet models in what we believe is the simplest possible manner, (2) show how these previous models can exhibit the mid-Pleistocene transition with the inclusion of CO₂ effects, (3) discuss the limitations of these previous bedrock models, and (4) illustrate the possibility of removing some of these limitations and accounting for further aspects of the paleoclimate record by using the full dynamical system that includes forced and free effects of CO₂, as well as effects of bedrock depression and Milankovitch forcing. As one example of a new possibility, with bedrock effects included in the full system we can obtain a solution characterized by irregularly spaced, intermittent episodes in which the behavior is dominated either by near-40 kyr period oscillations or by near-100 kyr periods (such as prevailed over the Pleistocene).  相似文献   

Academician A. P. Vinogradov 1895–1975     

Mikhail Ya. Marov 《Icarus》1977,30(1):239-241

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