Thermobaric Effect Research Articles

A 70-year perspective on water-mass transformation in the Greenland Sea: From thermobaric to thermal convection

The hydrography of the central Greenland Sea was reconstructed from observations including bottle measurements, Conductivity/ Temperature/ Depth (CTD) measurements, and Argo floats for the period 1950 to 2020. Greenland Sea Deep Water was renewed during bottom-reaching convection prior to the mid-1980s, facilitated by the thermobaric effect. During a period of shallow convection in the late 1980s and early 1990s, a stratification maximum formed and isolated the deep from the intermediate Greenland Sea. As a consequence, convection was limited to depths shallower than 2000m during the past decades and a new class of intermediate water formed instead of deep water. The initial cause for the formation of the stratification maximum was a near-surface freshwater anomaly. A subsequent, rapid temperature and salinity increase in the upper 2000m resulted in an overall density reduction of the intermediate water which strengthened the stratification maximum. Along with the transition from formation of deep water to formation of intermediate water, the Greenland Sea became temperature-stratified at intermediate depths. This regime-shift in stratification can be traced to increased temperature and salinity in the inflowing Atlantic-origin Water. Below the stratification maximum, the Greenland Sea Deep Water became warmer and more saline, predominantly caused by lateral mixing with deep water masses from adjacent basins. The hydrographic changes in the Greenland Sea were investigated in the context of a reduction of the sea-ice extent and associated changes in winter heat loss. While interannual variability of convection depth may depend on atmospheric forcing, we found that the decadal variability of water-mass transformation in the Greenland Sea was largely determined by the hydrographic structure of the water column.

Annual patterns of stratification, mixing and ventilation in long, deep, seasonally ice-covered François lake, British Columbia, Canada

François Lake is a long, deep, seasonally ice-covered, dimictic lake set in an east-west orientation in mid-British Columbia. As a baseline we here present data from a full-depth temperature mooring deployed at the lake’s mid-point in 2004–2005 and one full-depth conductivity-temperature-depth cast. We use these temperature records to define lake stability, scales of motion and the annual cycle of thermal stratification, mixing and deep-water ventilation. Owing to its length (110 km) both the Wedderburn and Lake numbers—indices of thermocline tilt and mixing under wind forcing—transition through critical values during fall and spring seasons, suggesting thermocline outcropping and strong turbulent mixing within the thermocline at these times. Owing to its depth (240 m) the decreasing temperature of maximum density (TMD) with depth (thermobaric effect) adds complexity to overturn events. Owing to its seasonal ice cover (2–3 months per year) the critical period for effective fall ventilation occurs before ice formation and concurrent wind shielding, while that of spring ventilation lies between the dates that the ice cover melts and the lake surface water warms above 4°C. While the lake undergoes full depth ventilation in both fall and spring, we show that both progress in distinct dynamical stages. Fall ventilation is more efficient than that of spring, and the transition temperature and resulting bottom temperature from fall to winter stratification (positive to inverse) and winter to spring stratification (inverse to positive) lies close to the temperature of maximum density calculated for the maximum depth of free and forced convection (in this case, closer to 3.7°C).

ON THE ANALYSİS OF OPERATİNG PRACTİCES OF LİQUEFİED GAS PİPELİNES

ON THE ANALYSİS OF OPERATİNG PRACTİCES OF LİQUEFİED GAS PİPELİNES

Atomic insight into the thermobaric effect of aluminized explosives

The addition of active metallic particles to common explosives can greatly extend high-temperature and high-pressure time of explosion, as the so-called thermobaric effect. However, the atomic details for this effect remain unclear. This work presents an atomic insight into the thermobaric explosion including anaerobic and aerobic stages by molecular dynamics simulations with a thermobaric explosive (TBX) model consisting of Al@Al2O3 nanoparticle and RDX. It is found that the thermobaric effect is originated from the Al oxidation by the intermediates and products of the RDX decomposition in the first anaerobic stage with a lot of Al-O, Al-H, Al-C and Al-N bonds formed, and the further oxidation by O2 in the aerobic stage with many C, H and N atoms extruded from the Al clusters. Interestingly, in terms of the components and structures of the final products, as well as the total heat release, the whole thermobaric explosion of the RDX-Al system can be regarded as the sum of the RDX decomposition and the Al oxidation in O2. Thereby, the energy design of a TBX can be simplified by considering the sum of the decomposition heat of the energetic compound involved and the combustion heat of the active metal. Regarding RDX, it plays a role in forming a high temperature and high pressure environment to promote the dispersion and combustion of Al particles. This work presents the atomic details responsible for the thermobaric effect and it is expected to pave a way to understand this effect.

Aluminized Enhanced Blast Explosive Based on Polysiloxane Binder

AbstractDrastic measures are taken in order to improve the properties of enhanced blast explosives. First, a binder with high reactivity as reducing agent is selected. The binder, platinum cure silicone, generates pyrophoric decomposition products in situ during the detonation. Arising problems with curing inhibition of the polymer are solved, as nanosized SiO2 is employed as hardening catalyst carrier. Quantum calculations show specific interactions of the binder and aluminum, forming the backbone of the composition. Furthermore, particle size distribution of the main fuel, aluminum powder, is selected so the Al will have enough time to heat, ignite and burn in the atmosphere, creating the thermobaric effect. Potassium perchlorate is employed as an oxidizer, as it reacts with detonation products faster than the widely used ammonium perchlorate. The resulting enhanced blast explosive is denoted as H‐TBX. High speed camera results show similar shock wave velocity 2.5 m from 2.7 kg TNT charge (2 ms after initiation) and 3.5 m from 2.65 kg H‐TBX charge (3 ms after initiation). In the open field, the H‐TBX generates 1.83 times higher peak pressure and 2 times higher impulse than TNT. These findings are compared with data from the literature for Tritonal, PBXN‐109 and AFX‐757. H‐TBX has improved parameters over the former generations of enhanced blast explosives and is currently used in multiple weapons systems.

Влияние структурных изменений нанокристаллов на механические свойства HPHT спеченного детонационного наноалмаза

The paper presents the results of studies on mechanical and structural properties of detonation nanodiamonds obtained by HPHT (high-pressure high-temperature) annealing within a wide temperature range. The experiments were carried out using a high-pressure “split-sphere” type apparatus (BARS) under 5 GPa and at 1100 –1500°С. It is established that the thermobaric treatment allows the production of strong composites with the local hardness up to 15 GPa. It is shown that the average value of microhardness increases with the sintering temperature. The temperature increase from 1100 to 1500°С results in an enhancement of the average value of microhardness from 8.8 to 12.2 GPa. The obtained materials are structurally inhomogeneous, regions of higher hardness are located in the central part of the samples. However, when the sintering temperature increases, dispersion of the microhardness decreases from 6.4 to 1.4 GPa which is caused by an improvement of the structural homogeneity of the composite with an increase in temperature. The thermobaric effect results in the growth of cores of diamond nanocrystals from 4.2 to 6.9 nm in samples obtained at 1500°С. It is highly probable that this growth occurs as a result of embedding of non-diamond phase carbon into the diamond core lattice during thermobaric sintering. This conclusion is made on the basis of X-ray data analysis. The specific feature of transformation of detonation nanodiamond shells consists in a simultaneous occurrence of two processes — desorption of volatile impure compounds and formation of a newly-formed diamond phase or ordered graphite around diamond cores. This effect results in the formation of open fragments of diamond cores capable of contacting with neighboring nanodiamond crystals thus binding diamond grains into a composite. Sintering temperature is an essential factor that affects the nanocrystal size as well as the mechanical properties and homogeneity of the composite.

Performance of Magnesium, Mg‐Al Alloy and Silicon in Thermobaric Explosives – A Comparison to Aluminium

AbstractA direct comparison is made between the effectiveness of Al, Mg, their alloy (Al3Mg4), and Si powders as additional fuels in explosives using the thermobaric effect. The experiment produced calorimetric measurements of the detonation heat and a record of the overpressure histories which were used to determine the quasistatic pressure (QSP) in an explosion chamber after the detonation of charges from mixtures containing 30 % fuel and 70 % RDX passivated with wax. The measured heat values indicate that Al−Mg alloy is a more effective additional fuel during anaerobic post‐detonation reactions than Al and Mg separately. Silicon also exothermically reacts with the detonation products, but the released heat only compensates for the lower amount of RDX in the charge. Similar to the calorimetric measurements, the lowest value of QSP was obtained for the mixture with Si powder. In contrast to anaerobic conditions, silicon proved to be an equally effective thermobaric additive as Al, Mg, and Al−Mg powders in air explosions.

Interannual Variability of the Outflow of Weddell Sea Bottom Water

AbstractThe Weddell Sea Bottom Water (WSBW) export from 1999 to 2019 displays distinct seasonal and interannual variability. From 2014 into 2017 a marked salinity decrease was recorded, with the lowest salinity, 34.615, attained in early 2016. The reduced salinity is derived from the V‐shaped trough formed by a double front along the shelf break of the Weddell Gyre's western boundary, which is filled with a blend of surface water and modified Weddell Deep Water. We estimate that when the V‐shaped apex attains a depth of greater than ~700 m, the thermobaric effect promotes its descent into the WSBW. We propose that this occurred during anomalously strong cyclonic wind stress curl over the Weddell Gyre from 2014 into 2017, which increased the intensity of the gyre and its western boundary current, deepening the V‐shape trough. The WSBW salinity increased to its prior to 2014 values as the wind stress relaxed in 2018.

Impact of seawater equation of state on the simulation of Atlantic Meridional Overturning Circulation

The Atlantic Meridional Overturning Circulation (AMOC) plays a central role in the decadal variability of global and regional climate through changing poleward transport of heat. However, realistic simulation of the AMOC, i.e., its strength and spatial structure, remains a challenge for ocean general circulation models (OGCMs) and coupled climate models. Here, we investigate how the simulated AMOC could be affected by improved accuracy of the seawater equation of state (EOS) with an OGCM. Two EOSs used in this study: the UNESCO EOS80, and the “stiffened” EOS derived from the compressibility of sea water and the UNESCO EOS80. Compared to the model using the UNESCO EOS80, the model using the “stiffened” EOS yields stronger deep convection in the Labrador Sea, the Irminger-Iceland-Scotland Basin, and the Greenland-Iceland-Norwegian (GIN) seas, which leads to an improvement in the simulation of the AMOC: Along 26.5°N, the maximum transport is increased from 14.9 to 17.4 Sv and the interface between the upper clockwise cell and lower counterclockwise cell is deepened from 2.8 to 3.3 km, both matching the observations better. Taken the Labrador Sea as an example, the processes, including both direct and indirect causes, that in part responsible for the improved AMOC are as follows. The use of “stiffened” EOS increases the density throughout the water column and weakens the stability of sea water. Moreover, the enhanced cabbeling and thermobaric effect strengthen the vertical advection, intensifying the deep convection and increasing formation of deep water, which eventually improves the simulation of the AMOC. The intensified AMOC, in turn, speeds up the surface return flow, transporting more warm and saline water to the high latitudes in the North Atlantic, which contributes to the densification of surface water. Similar analyses can be applied to the Iceland-Scotland Basin and GIN seas. Thus, the enhanced deep convection and formation of deep water in the Labrador Sea, as well as in the Iceland–Scotland Basin and GIN seas, improve the simulated AMOC.

Heat balance of Lake Baikal and the relationship of its ice-thermal and water regime with global atmospheric circulation in the Northern Hemisphere during the modern period

The article presents a summary of the most important results obtained during the studies of the heat balance at Lake Baikal since the 1930s. The systematic regime measurements of water temperature initiated in Limnological Institute since 1970 indicated the features of the spatial structure and temporal changes in the elements of the Baikal heat balance. We have determined the magnitude of the annual evaporation from the surface of Lake Baikal by the independent method considering the data on temperature of the water column. We have investigated one of the main renewal processes of deep and near-bottom Baikal waters associated with thermobaric effect. As a result of this effect, the water renewal and aeration in the near-bottom layer annually occurs under certain hydrological conditions. We have determined the vertical flows of mass, heat and gas exchange of the upper and deep layers in Lake Baikal. We have studied the effect of changes in the characteristics (indices) of the atmospheric circulation in the Northern Hemisphere on the variability of the characteristics of climate and ice-thermal regime at Baikal, i.e. air temperature and water surface temperature, ice thickness, as well as dates of ice phenomena during the modern period. Anomalies of the atmospheric circulation are most obvious in the ice processes. We have found the relationship between the water temperature of the warm (May-September) period and the indicators of the zonal circulation (positive relationship), as well as indices of the formations blocking the western transfer (negative relationship). There is an obvious effect on the water surface temperature of the winter circulation indices. We have shown that these changes are associated with the fluctuations in the intensity of the zonal circulation and the baric formations blocking them. There is the effect of circulation on the moisture characteristics (precipitation and runoff), but it is complicated by large differences in climate within the Baikal catchment area.

Thermobaric Effects of Cast Composite Explosives of Different Charge Masses and Dimensions

The aim of this research was to determine the thermobaric effect of cast composite explosives, with different masses and dimensions of the chosen explosive charges. This was done by measuring the shock wave parameters in air (maximum overpressure and pressure impulse) and quantifying the thermal effect (temperature-time dependence), at different distances from the centre of the detonation. The chosen thermobaric explosive composition, TBE-3, was characterized. Its density, detonation velocity and viscosity-time dependence were determined. Experimental samples of different masses and calibres were prepared. The shock wave parameters in air were determined in field tests, by measuring the overpressure by piezo-electric pressure transducers. The detonation and the expansion of the explosion products were filmed by a TV high-speed camera, Phantom V9. An infrared (IR) camera FLIR SC7200 was used for recording the IR scene of the explosions and for tracking the thermal effects by a thermographic technique, i.e. thermal imaging. This work is an initial step towards establishing a method for the quantification of the thermal effects of a thermobaric detonation.

Energetics of lateral eddy diffusion/advection: Part II. Numerical diffusion/diffusivity and gravitational potential energy change due to isopycnal diffusion

Study of oceanic circulation and climate requires models which can simulate tracer eddy diffusion and advection accurately. It is shown that the traditional Eulerian coordinates can introduce large artificial horizontal diffusivity/viscosity due to the incorrect alignment of the axis. Therefore, such models can smear sharp fronts and introduce other numerical artifacts. For simulation with relatively low resolution, large lateral diffusion was explicitly used in models; therefore, such numerical diffusion may not be a problem. However, with the increase of horizontal resolution, the artificial diffusivity/viscosity associated with horizontal advection in the commonly used Eulerian coordinates may become one of the most challenging obstacles for modeling the ocean circulation accurately. Isopycnal eddy diffusion (mixing) has been widely used in numerical models. The common wisdom is that mixing along isopycnal is energy free. However, a careful examination reveals that this is not the case. In fact, eddy diffusion can be conceptually separated into two steps: stirring and subscale diffusion. Due to the thermobaric effect, stirring, or exchanging water masses, along isopycnal surface is associated with the change of GPE in the mean state. This is a new type of instability, called the thermobaric instability. In addition, due to cabbeling subscale diffusion of water parcels always leads to the release of GPE. The release of GPE due to isopycnal stirring and subscale diffusion may lead to the thermobaric instability.

Energy Conversion, Mixing Energy, and Neutral Surfaces with a Nonlinear Equation of State

Abstract A local neutral plane is defined so that a water parcel that is displaced adiabatically a small distance along the plane continues to have the same density as the surrounding water. Since such a displacement does not change the density field or the gravitational potential energy, it is generally assumed that it does not produce a restoring buoyancy force. However, it is here shown that because of the nonlinear character of the equation of state (in particular the thermobaric effect) such a neutral displacement is accompanied by a conversion between internal energy E and gravitational potential energy U, and an equal conversion between U and kinetic energy K. While there is thus no net change of U, K does change. This implies that a force is in fact required for the displacement. It is further shown that displacements that are orthogonal to a vector P do not induce conversion between U and K, and therefore do not require a force. Analogously to neutral surfaces, which are defined to be approximately orthogonal to the dianeutral vector N, one may define “P surfaces” to be approximately orthogonal to P. These P surfaces are intermediate between neutral surfaces and surfaces of constant σ0 (potential density reference to the surface). If the equation of state is linear, there exists a well-known expression for the mixing energy in terms of the diapycnal flow. This expression is here generalized for a general nonlinear equation of state. The generalized expression involves the velocity component along P. Since P is not orthogonal to neutral surfaces, this means that stationary flow along neutral surfaces in general requires mixing energy.

Thermobaric effect on slantwise convection in cold seawater

Thermobaric effect on slantwise convection in cold seawater

Thermobaric effect on slantwise convection in cold seawater

A theoretical investigation shows that the pressure dependence of the thermal expansion coefficient (the thermobaric effect) acts to destabilize stratified geostrophic flows when both temperature and salinity contribute positively to the vertical stability. For vertical stability where the salinity contributes negatively, the thermobaric effect may act to stabilize the flow. The considered disturbances are small-amplitude two-dimensional rolls with axes aligned along the basic geostrophic current, and the growth mechanism is symmetric baroclinic instability. The boundaries of the marginally stable convection cells are essentially parallel to the slanting isopycnals of the basic state; therefore, the term slantwise convection is used to describe this phenomenon. Furthermore, the thermobaric effect induces a shift of the centres of the convection cells towards the lower part of the fluid layer, as previously demonstrated for buoyancy-driven convection. The width of the marginally stable cells is small and determined by turbulent diffusion processes in the fluid.

Rapid climate change and conditional instability of the glacial deep ocean from the thermobaric effect and geothermal heating

Previous results from deep-sea pore fluid data demonstrate that the glacial deep ocean was filled with salty, cold water from the South. This salinity stratification of the ocean allows for the possible accumulation of geothermal heat in the deep-sea and could result in a water column with cold fresh water on top of warm salty water and with a corresponding increase in potential energy. For an idealized 4000 dbar two-layer water column, we calculate that there are ∼10 6 J/m 2 (∼0.2 J/kg) of potential energy available when a 0.4 psu salinity contrast is balanced by a ∼2 °C temperature difference. This salt-based storage of heat at depth is analogous to Convectively Available Potential Energy (CAPE) in the atmosphere. The “thermobaric effect” in the seawater equation of state can cause this potential energy to be released catastrophically. Because deep ocean stratification was dominated by salinity at the Last Glacial Maximum (LGM), the glacial climate is more sensitive to charging this “thermobaric capacitor” and can plausibly explain many aspects of the record of rapid climate change. Our mechanism could account for the grouping of Dansgaard/Oeschger events into Bond Cycles and for the different patterns of warming observed in ice cores from separate hemispheres.

Equations of Motion Using Thermodynamic Coordinates

The forms of the primitive equations of motion and continuity are obtained when an arbitrary thermodynamic state variable=mrestricted only to be vertically monotonic=mis used as the vertical coordinate. Natural generalizations of the Montgomery and Exner functions suggest themselves. For a multicomponent fluid like seawater the dependence of the coordinate on salinity, coupled with the thermobaric effect, generates contributions to the momentum balance from the salinity gradient, multiplied by a thermodynamic coefficient that can be completely described given the coordinate variable and the equation of state. In the vorticity balance this term produces a contribution identified with the baroclinicity vector. Only when the coordinate variable is a function only of pressure and in situ specific volume does the coefficient of salinity gradient vanish and the baroclinicity vector disappear. This coefficient is explicitly calculated and displayed for potential specific volume as thermodynamic coordinate, and for patched potential specific volume, where different reference pressures are used in various pressure subranges. Except within a few hundred decibars of the reference pressures, the salinity-gradient coefficient is not negligible and ought to be taken into account in ocean circulation models.

Modeling of deep-water renewal through cold convective plumes

In only a few regions in the world ocean, surface water is transformed into deep water by open ocean convection. In this paper, small areas of vertical flow, or plumes, are studied using a steady-state model, integrated in streamline coordinates. We use an entrainment hypothesis based on knowledge about in-mixing of water across the shear zone from an area of low turbulence into an area of high turbulence. This results in a model using conservation equations for momentum, heat and salt, and a nonlinear equation of state. Effects of earth rotation are included. The depth reached by surface water when moving through stationary plumes is predicted, and found strongly dependent on the properties in the surface layer. This layer has to be colder but only slightly denser than the water just below it to be a source for steady-state plumes. The thermobaric effect, the dependency of compressibility on the temperature, plays a major role for the plume penetration depth. In weakly stratified cold water, like in the Greenland Sea, deep convection is found to be possible and efficient through steady-state plumes. Initial excess density of less than 5×10 −3 kg m −3 , caused by low temperature, can give convection deeper than 1500 m through plumes with horizontal scales of a few hundred meters and vertical velocities of order a few tens of centimeters per second.

On thermobaric production of potential vorticity in the ocean

Because of the two-constituent nature of seawater, there is no conservative potential vorticityfor the ocean, even when viscous and diffusive effects are ignored. Specifically, nonconservationarises in association with the thermobaric effect, which is related to nonlinearities in the equationof state. While this is well-known, it is generally supposed that this forcing is far too small tobe of importance for most problems of interest. A careful scale analysis is presented to suggestthat thermobaric forcing is larger than is generally supposed, particularly at the high wavenumberend of the spectrum. The spatial structure of the thermobaric potential vorticity sourceis dependent on an arbitrary choice, such as the choice of a reference pressure in the definitionof potential vorticity. To address the effect of thermobaricity on the dynamics, which must beindependent of arbitrarily chosen parameters, it therefore seems desirable to consider howbalanced dynamical systems are affected. In this spirit, an analog to quasigeostrophy that isapplicable to thermobaric fluids is derived and its conservation properties are discussed. It isargued that thermobaricity can lead to O(1) changes in the vorticity distribution at the highwavenumber end of the spectrum. Additionally, integral constraints that can influence basinscale circulation are affected. For example, isopycnal mixing affects the (QG) energetics andpotential enstrophy is lost as a conserved quantity. The size of the enstrophy source (or sink)and the wave number at which thermobaric effects produce an O(1) effect both depend on thesize of a nondimensional parameter that is introduced. This parameter, although typically small,can be large with respect to the Rossby number appropriate to the mid-latitude eddy field.That is, it is suggested that thermobaric effects may be larger than finite Rossby number effectson the dynamics of the mid-latitude eddy field, particularly below the thermocline.

Thermobaric effect on buoyancy‐driven convection in cold seawater

The equations governing buoyancy‐driven convection in a rotating horizontal fluid layer, where the thermal expansion coefficient is a function of pressure (here, depth), have been derived. The results confirm the validity of the Boussinesq approximation. Furthermore, the adiabatic lapse rate for cold seawater is shown to be so small that it can usually be neglected in comparison to the in situ temperature gradient. For purely thermal convection a linear perturbation analysis shows that a weak thermobaric effect acts as a destabilizing influence on the Rayleigh‐Bénard problem. This is also the case when Earth's rotation is taken into account. In particular, for marginal stability in the absence of rotation, it is shown that two‐dimensional convection cells are asymmetric with respect to the midlayer plane, with stronger circulation in the deeper part of the layer. This effect is also revealed by two‐dimensional, nonlinear numerical computations, when the layer is stratified by opposing gradients of heat (acting destabilizing) and salt (acting stabilizing). For thermobaric convection, i.e., in cases where the layer would have been stable in the absence of the thermobaric effect, the computed cell pattern is seen to be displaced toward the deeper part of the layer. Furthermore, the cell width increases with increasing thermobaric strength. It is suggested that thermobaric convection may act in conjunction with haline convection due to freezing in the process of vertical mixing and deep water formation in polar areas.