Amount Of Available Potential Energy Research Articles

Grain-resolving simulations of submerged cohesive granular collapse

We investigate the submerged collapse of weakly polydisperse, loosely packed cohesive granular columns, as a function of aspect ratio and cohesive force strength, via grain-resolving direct numerical simulations. The cohesive forces act to prevent the detachment of individual particles from the main body of the collapsing column, reduce its front velocity, and yield a shorter and thicker final deposit. All of these effects can be captured accurately across a broad range of parameters by piecewise power-law relationships. The cohesive forces reduce significantly the amount of available potential energy released by the particles. For shallow columns, the particle and fluid kinetic energy decreases for stronger cohesion. For tall columns, on the other hand, moderate cohesive forces increase the maximum particle kinetic energy, since they accelerate the initial free-fall of the upper column section. Only for larger cohesive forces does the peak kinetic energy of the particles decrease. Computational particle tracking indicates that the cohesive forces reduce the mixing of particles within the collapsing column, and it identifies the regions of origin of those particles that travel the farthest. The simulations demonstrate that cohesion promotes aggregation and the formation of aggregates. Furthermore, they provide complete information on the temporally and spatially evolving network of cohesive and direct contact force bonds. While the normal contact forces are aligned primarily in the vertical direction, the cohesive bonds adjust their preferred spatial orientation throughout the collapse. They result in a net macroscopic stress that counteracts deformation and slows the spreading of the advancing particle front.

Vertical mixing and coherent anticyclones in the ocean: the role of stratification

Abstract. The role played by wind-forced anticyclones in the vertical transport and mixing at the ocean mesoscale is investigated with a primitive-equation numerical model in an idealized configuration. The focus of this work is to determine how the stratification impacts such transport. The flows, forced only at the surface by an idealized wind forcing, are predominantly horizontal and, on average, quasigeostrophic. Inside vortex cores and intense filaments, however, the dynamics is strongly ageostrophic. Mesoscale anticyclones appear as "islands" of increased penetration of wind energy into the ocean interior and they represent the maxima of available potential energy. The amount of available potential energy is directly correlated with the degree of stratification. The wind energy injected at the surface is transferred at depth through the generation and subsequent straining effect of Vortex Rossby Waves (VRWs), and through near-inertial internal oscillations trapped inside anticyclonic vortices. Both these mechanisms are affected by stratification. Stronger transfer but larger confinement close to the surface is found when the stratification is stronger. For weaker stratification, vertical mixing close to the surface is less intense but below about 150 m attains substantially higher values due to an increased contribution of both VRWs, whose time scale is on the order of few days, and of near-inertial motions, with a time scale of few hours.

Vertical Velocities and Available Potential Energy Generated by Landscape Variability—Theory

Abstract It is shown that landscape variability decreases the temperature in the surface layer when, through mesoscale flow, cool air intrudes over warm patches, lifting warm air and weakening the static stability of the upper part of the planetary boundary layer. This mechanism generates regions of upward vertical motion and a sizable amount of available potential energy and can make the environment of the lower troposphere more favorable to cloud formation. This process is enhanced by light ambient wind through the generation of trapped propagating waves, which penetrate into the midtropospheric levels, transporting upward the thermal perturbations and weakening the static stability around the top of the boundary layer. At moderate ambient wind speeds, the presence of surface roughness changes strengthens the wave activity, further favoring the vertical transport of the thermal perturbations. When the intensity of the ambient wind is larger than 5 m s−1, the vertical velocities induced by the surface roughness changes prevail over those induced by the diabatic flux changes. The analysis is performed using a linear theory in which the mesoscale dynamics are forced by the diurnal diabatic sensible heat flux and by the surface stress. Results are shown as a function of ambient flow intensity and of the wavelength of a sinusoidal landscape variability.

Annual and Interdecadal Variability of the Available Potential Energy in the Black Sea

On the basis of the climatic data array on temperature and salinity including the data of observations carried out at 102,000 oceanographic stations in 1910–1998, we estimate the amount of available potential energy of large-scale processes in the 0–300-m layer of the Black Sea and study its annual variability. The annual average amount of available potential energy in the active 0–300-m layer is equal to 13.5×1014 J, its maximum amount attained in March is 25×1014 J, and its minimum amount attained in August is 8×1014 J. In the autumn–winter period, the density of available potential energy in the 0–50-m layer increases and its maximum is attained in December–January (30 J/m3). Beginning with January, the density of available potential energy increases in the layer of the main pycnocline (50–150 m). Its maximum is attained in March (50 J/m3) and then this quantity decreases till August (down to 14 J/m3). In August, we study the interdecadal variability of the available potential energy in the 50–300-m layer by using the data accumulated for decadal periods with five-year shifts in 1956–1995. The maximum variability is observed at a depth of 100 m. The maximum average (over the sea) amounts of available potential energy were observed in 1961–1970 and 1986–1995. The minimum amounts were recorded in 1976–1985.

Some dynamical consequences of Greenhouse gas warming

Abstract The change in December‐February climate simulated by the CCC GCM for a doubling of CO2 is viewed from a Northern Hemisphere middle‐latitude persepctive. The simulated change in temperature is such as to reduce equator‐to‐pole and ocean‐to‐land temperature gradients in the body of the troposphere and this is expected to result in less baroclinicity and baroclinic instability, weaker eddies and transports and generally to a decrease in synoptic activity or, in other words, to more “summer‐like” conditions. The overall “rate of working” of the atmosphere, as measured by the generation of available potential energy, its conversion to kinetic energy and subsequent dissipation, decreases by some 12%. However, while the amount of available potential energy in the atmosphere decreases by about the same amount, the amount of kinetic energy is unchanged. Differences to the mean zonal, standing and transient eddy components of available potential and kinetic energies and to their rates of generation and conversion show that the energy cycle has changed in ways that might not be immediately expected. Despite the general decrease in activity, the net poleward transport of energy by the atmosphere is remarkably unchanged. This is accomplished with the expected decrease in the transport of dry static energy being off‐set by an increase in latent energy transport. This is true both for mean zonal and eddy transports. That the same amount of energy is transported by a generally less active atmosphere shows that, in a sense, the flow structures are more “efficient” in the warmer climate and calculations are made to quantify this. The transport of energy in latent form is much more efficient due to the strong increase in moisture content that accompanies the temperature increase.

Downwelling-Front Instability and Eddy Formation in the Eastern Mediterranean

Abstract The instability of the downwelling front along the southern coast of Asia Minor is studied with a multimode quasigeostrophic model. Linear analysis shows that the most unstable wave has a length of about 100 km, The wavelength depends only very weakly on the transversal scale of the front. The wave period is larger by an order of magnitude than the e-folding time; that is, rapid local growth occurs with little propagation. The growth rate is proportional to the maximum of the speed of the downwelling westward jet. The evolution of the frontal waves can be divided into three stages. At first, the evolution is mainly due to linear instability; the second stage is characterized by closed eddy formation; and finally, isolated eddies separate from the front and penetrate into the open sea. The largest amount of available potential energy is transferred to kinetic energy and into the barotropic mode during the second, eddy-forming stage, when several dipoles develop in this mode. The formation of antic...

A two-dimensional model of mesoscale frontogenesis in the ocean

A two-dimensional primitive equation model conserving potential vorticity is used to simulate the effect of a horizontal barotropic deformation field on a pre-existing isopycnic potential vorticity gradient. The novel feature of the prognostic model is that it accurately describes the development of the density and velocity distributions up to local Rossby number 0.5 and beyond. The model coordinates are based in the vertical on quasi-isopycnic vertical coordinates and in the horizontal on geostrophic coordinates. The model is integrated forward in time for three days creating a density front and a jet of 0.4 m s−1 in the surface layers. Cross-jet velocities are one order of magnitude smaller. Conservation of potential vorticity leads to a modulation of spacing between isopycnals as both the cyclonic and anticyclonic vorticity associated with the horizontal shear of the accelerating jet increase. Vortex stretching and compression sustain a strong vertical circulation. The paper shows how the jet kinetic energy is limited by the amount of available potential energy in a catchment area defined by the extent of the region of confluence. The jet becomes shallower as frontogenesis approaches this limit. The model is also applicable to the development of permanent streams in the large-scale circulation of the upper ocean, by slow (order one month) frontogenesis due to gyre-scale deformation acting on an isopycnic potential vorticity gradient in the seasonal thermocline. The vigorous upwelling on the anticyclonic side of the jet raises nutrients through the euphotic zone, increasing primary productivity. This explains observed meoscale modulations of biomass.

A two‐dimensional model of mesoscale frontogenesis in the ocean

AbstractA two‐dimensional primitive equation model conserving potential vorticity is used to simulate the effect of a horizontal barotropic deformation field on a pre‐existing isopycnic potential vorticity gradient. The novel feature of the prognostic model is that it accurately describes the development of the density and velocity distributions up to local Rossby number 0.5 and beyond. The model coordinates are based in the vertical on quasi‐isopycnic vertical coordinates and in the horizontal on geostrophic coordinates. The model is integrated forward in time for three days creating a density front and a jet of 0.4 m s−1 in the surface layers. Cross‐jet velocities are one order of magnitude smaller. Conservation of potential vorticity leads to a modulation of spacing between isopycnals as both the cyclonic and anticyclonic vorticity associated with the horizontal shear of the accelerating jet increase. Vortex stretching and compression sustain a strong vertical circulation. The paper shows how the jet kinetic energy is limited by the amount of available potential energy in a catchment area defined by the extent of the region of confluence. The jet becomes shallower as frontogenesis approaches this limit.The model is also applicable to the development of permanent streams in the large‐scale circulation of the upper ocean, by slow (order one month) frontogenesis due to gyre‐scale deformation acting on an isopycnic potential vorticity gradient in the seasonal thermocline.The vigorous upwelling on the anticyclonic side of the jet raises nutrients through the euphotic zone, increasing primary productivity. This explains observed meoscale modulations of biomass.

Heat, Water, and Vorticity Balance in Frontal Zones

The data source for this study is a collection of five years of serial upper-air soundings taken during storms at five stations in the Southern California coastal and offshore region, along with supporting aerial, radar, and surface precipitation observations. Detailed analyses of frontal systems revealed mesoscale motions and processes which are an important and integral part of the frontal structure. In particular, the flow pattern within the prefrontal precipitation region is found to be characterized by waves aloft and a matching cell structure below, with wavelength of 200 to 300 km and with crusts oriented parallel to the front. Within these cells are found small convection bands with which are associated sharp peaks in the precipitation distribution. The overall pattern slopes aloft over the front, and this slope, along with horizontal and vertical mixing, is an essential element in the dynamic balance within the frontal zone. The intensity of the mesoscale vertical motion responsible for clouds and precipitation in the frontal zone appears to have some association with the degree of convective activity. In the stronger fronts, vertical velocity peaks of 20 cm sec−1 or more are found to be the rule. The thermal balance is dominated largely by vertical differences in horizontal advection which are balanced by convective heat exchange. A strong, low-level current of warm air from the south overridden by cold air from the west determines to varying degrees the convective instability and results in a considerable amount of available potential energy being converted directly into convection-scale kinetic energy, thus by-passing its conversion to the cyclone-scale kinetic energy. In fronts possessing greater stability, vertical velocities are less and the eastward movement of the front is greater, suggesting that in these cases the broad-scale deformation of the cyclone-scale thermal pattern, which controls the deepening and the occlusion processes, is accelerated.