Mean Potential Energy Research Articles

The Global Atmospheric Energy Cycle in TaiESM1: Present and Future

AbstractThe Lorenz Energy Cycle (LEC) in the Taiwan Earth System Model Version 1 (TaiESM1) historical simulation is calculated and compared with ERA5 to evaluate the model performance from the thermodynamic aspect. The future change of LEC is accessed by comparing the SSP5‐8.5 and historical simulations in TaiESM1. TaiESM1 reasonably simulates the global mean, seasonal cycle, and spatial patterns of the energy reservoirs with larger values in the mean energy components and smaller in the eddy energy components. The energy cycle in TaiESM1 is about 35%–45% stronger than ERA5, except from December to February. The impact of global warming on the LEC is different at the vertical levels. The influence of meridional temperature gradient change is the dominant factor in the intensity of the energy cycle, and the change in static stability only contributes to the lower troposphere. Lifting the tropopause in the tropics increases the meridional temperature gradient and produces more zonal mean potential energy (PM) in the upper troposphere. PM is the primary driver of the LEC and leads to a more active energy cycle in the upper troposphere. As the tropical tropospheric depth increases and the mid‐latitude eddy activities become more active, more (less) energy is stored in the upper (lower) troposphere, and the energy conversion processes tend to become stronger (weaker) in the upper (lower) troposphere.

Palmar Displacement in Distal Radius Fractures following Extension Injuries of the Wrist

Fractures of the distal radius have been traditionally classified based on the suspected mechanism of injury. Among clinicians, the terms "Colles" and "Smith" fractures are commonly used to refer to a distal radius fracture that is either displaced to the dorsal (Colles) or palmar (Smith) side of the radius. When analysing x-rays, it is not uncommon for a Smith fracture to be detected in cases where patients describe a fall on the wrist in an extended position. Thus, the question arises how a flexion-type fracture can occur after an extension injury. So far, only little research has been conducted into this subject. The aim of this study was to analyse the mechanisms of injury that lead to various types of distal radius fractures. Particular emphasis was placed on "Smith" fractures and on the biomechanical, physiological and anatomical characteristics that contribute to their occurrence. To assess these relationships, data of fractures were collected following a life-like fracture simulation using a "drop-bench" in non-formalin fixated human specimens. These fractures were produced between January 2016 and December 2021. Biographic data of all specimens used were available. Additionally, all biomechanical and physical characteristics of the fracture simulation were fully documented. Of the 122 specimens with a full data set, 17 (13.9%) fractures were determined to be Smith fractures based on their radiological appearance. In 10 of these flexion fractures, the wrist was set in dorsal extension. The mean angle of extension was 86.3 degrees for flexion fractures compared to 90.5 degrees for extension fractures. Six out of 10 Smith-type fractures that were set in dorsal extension were also exposed to pronation, whereas only one was exposed to supination. The mean potential energy for fracture creation was 168.0 joules for Smith fractures in dorsal extension, whereas all other fractures showed a mean of 185.2 joules. It can be concluded that a Smith fracture is not limited to being the result of a fall on the wrist in a flexed position. The same fracture may also be the result of a fall with the wrist in an extended position if certain physical factors are applicable.

Non-relativistic energy spectra of and diatomic molecules confined in a modified Scarf potential via supersymmetric WKB approach

In this research, the energy equation of the Schrodinger equation with the modified Scarf potential has been obtained using the supersymmetric WKB (SWKB) approach. The Pekeris approximation has been applied to enable the analytical solution. The energy equation was applied to determine the rovibrational states of two diatomic molecules such as O 2 + ( X 2 Π g ) and N 2 ( X 1 Σ g + ) . The average kinetic and potential energies were computed via the Hellman-Feynman theorem. The analytical result of the energy equation obtained coincides with the work reported in earlier literature where the authors had applied a different approach. The energy eigenvalues for the studied molecules were found to agree with the ones obtained using the Teitz-Hua molecular potential, the deformed modified Rosen-Morse (DMRM) potential, the Morse potential and the Rydberg-Klein-Rees data points. For the energy spectra, we found average absolute deviations of 0.129515% for O 2 + ( X 2 Π g ) and 1.834993% for N 2 ( X 1 Σ g + ) molecules respectively. The energy spectra increase as the quantum numbers increase up to the dissociation limit before decreasing. For the molecules, the atoms were found to possess an oscillatory-type motion where an increase in the mean kinetic energy resulted in a decrease in mean potential energy and vice-visa.

Investigation of mechanical behavior of porous carbon-based matrix by molecular dynamics simulation: Effects of Si doping

Understanding the mechanical properties of porous carbon-based materials can lead to advancements in various applications, including energy storage, filtration, and lightweight structural components. Also, investigating how silicon doping affects these materials can help optimize their mechanical properties, potentially improving strength, durability, and other performance metrics. This research investigated the effects of atomic doping (Si particle up to 10 %) on the mechanical properties of the porous carbon matrix using molecular dynamics methods. Young's modulus, ultimate strength, radial distribution function, interaction energy, mean square displacement and potential energy of designed samples were reported. MD outputs predict the Si doping process improved the mechanical performance of porous structures. Numerically, Young's modulus of the C-based porous matrix increased from 234.33 GPa to 363.82 GPa by 5 % Si inserted into a pristine porous sample. Also, the ultimate strength increases from 48.54 to 115.93 GPa with increasing Si doping from 1 % to 5 %. Silicon doping enhances the bonding strength and reduces defects in the carbon matrix, leading to improved stiffness and load-bearing capacity. This results in significant increases in mechanical performance. However, excess Si may disrupt the optimal bonding network, leading to weaker connections within the matrix. Also, considering the negative value of potential energy in different doping percentages, it can be concluded that the amount of doping added up to 10 % does not disturb the initial structure and stability of the system, and the structure still has structural stability. So, we expected our introduced atomic samples to be used in actual applications.

Loose bonding induced ultralow lattice thermal conductivity of a metallic crystal KNaRb

In the domain of metallic systems, electronic thermal conductivity typically governs heat transfer, while lattice (phononic) thermal conductivity (LTC) remains non-negligible magnitude. This study introduces the exceptional metallic material, cubic half-Heusler-type KNaRb, via phonon Boltzmann transport equation (BTE) resolution and first-principles calculations. KNaRb exhibits an ultralow LTC of 0.114 W/mK at room temperature, comparable to the lowest reported for metallic materials, contributing merely 0.66 % to overall thermal transport. Analysis attributes KNaRb's low LTC to low group velocity and strong anharmonicity, originating from its loosely bonded electronic structure. Acoustic modes, primarily from Rb atoms, dominate thermal transport. Examination of mean square displacement and potential energy profiles reveals significant movement of loosely bonded Rb atoms within KNaRb, acting as intrinsic "rattlers," inducing pronounced phonon anharmonicity and ultrashort lifetimes. This study advances understanding of heat conduction in metals, offering insights into materials with extremely low lattice thermal conductivity for potential future applications.

MD Simulation of Water Using a Rigid Body Description Requires a Small Time Step to Ensure Equipartition.

In simulations of aqueous systems, it is common to freeze the bond vibration and angle bending modes in water to allow for a longer time step δt for integrating the equations of motion. Thus, δt = 2 fs is often used in simulating rigid models of water. We simulate the SPC/E model of water using δt from 0.5 to 3.0 fs and up to 4 fs using hydrogen mass repartitioning. In these simulations, we find that for all but δt = 0.5 fs, equipartition is not obtained between translational and rotational modes, with the rotational modes exhibiting a lower temperature than the translation modes. To probe the reasons for the lack of equipartition, we study the autocorrelation of the translational velocity of the center of mass and the angular velocity of the rigid water molecule, respectively. We find that the rotational relaxation occurs on a timescale comparable to vibrational periods, calling into question the original motivations for freezing the vibrations. Furthermore, a time step with δt ≥ 1 fs is not able to capture accurately the fast rotational relaxation, which reveals its impact as an effective slowing-down of rotational relaxation. The fluctuation-dissipation relation then leads to the conclusion that the rotational temperature should be cooler for δt greater than the reference value of 0.5 fs. Consideration of fluctuation-dissipation in equilibrium molecular dynamics simulations also emphasizes the need to capture the temporal evolution of fluctuations with fidelity and the role of δt in this regard. The time step also influences the solution thermodynamic properties: both the mean system potential energies and the excess entropy of hydration of a soft repulsive cavity are sensitive to δt.

Optimization of Longitudinal Motions of an Elastic Rod Using Periodically Distributed Piezoelectric Forces

The longitudinal vibrations of an elastic rod controlled by a distributed force, which is applied to individual sections of the rod, are studied. It is assumed that the force varies in space in a piecewise constant manner. Such a mechanical system can be implemented using piezoactuators attached along the rod. The dynamics of the system is determined from the solution of the variational problem following the method of integrodifferential relations. The variational problem is solved analytically. To do this, traveling waves of the d’Alembert type are introduced on the space-time mesh, which determine continuous displacements and a dynamic potential. The latter relates the momentum density and stresses. A control problem is posed under the condition of the weighted minimization of the vibrational energy stored by the rod at the terminal time instant, and the mean potential energy generated by the control actions. The extremal motion and the corresponding control law are found explicitly by solving the Euler–Lagrange equations. As an example, the control capabilities for certain configurations of piezoelectric elements are studied.

Structural morphology and surface recrystallization properties of GaN nanoparticles with different sizes during sintering

GaN is a promising third-generation semiconductor material for fabricating nanodevices with nanoscale dimensions. In particular, thick-film sensors fabricated with GaN nanoparticles (NPs) have good gas-sensing characteristics. This study used molecular dynamics simulation to investigate the effect of temperature and size on the structural morphology and surface recrystallization of GaN NPs during sintering. The diffusion behavior and changes in the structural morphology of atoms were analyzed based on the shrinkage ratio, mean square displacement, potential energy, and other methods. The results show that during sintering, the surface of two GaN NPs experienced recrystallization, which expanded with increasing temperature; however, the obvious sintering phenomenon occurred at 3000 K. Interestingly, the surface recrystallization of NPs exhibited a lamellar structure formed through a specific stacking method of the crystal structure. However, when the size of one of the two NPs was reduced, the small NP rapidly melted and was induced to crystallize into a complete NP (having the same crystal orientation as the large NP) by the large NP. Moreover, NPs underwent rigid-body rotation and relative rotation during sintering; however, plastic deformation and dislocations resulting from rotation were only found in the neck of NPs of the same size. The study results provide valuable insights at the atomic scale regarding the sintering of GaN NPs and a useful reference for preparing and processing nanodevices.

Lorenz Energy Cycle: Another Way to Understand the Atmospheric Circulation on Tidally Locked Terrestrial Planets

In this study, we employ and modify the Lorenz energy cycle (LEC) framework as another way to understand the atmospheric circulation on tidally locked terrestrial planets. It well describes the atmospheric general circulation in the perspective of energy transformation involved with several dynamical processes. We find that on rapidly rotating, tidally locked terrestrial planets, the mean potential energy (P M) and eddy potential energy (P E) are comparable to those on Earth, as they have similar steep meridional temperature gradients. The mean kinetic energy (K M) and eddy kinetic energy (K E) are larger than those on Earth, related to stronger winds. The two conversion paths, P M → P E → K E and P M → K M → K E, are both efficient. The former is associated with strong baroclinic instabilities, and the latter is associated with Hadley cells. On slowly rotating, tidally locked terrestrial planets, weak temperature gradients in the free atmosphere and strong nightside temperature inversion make P M and P E much smaller than on Earth. Meanwhile, a large day–night surface temperature contrast and small rotation rate make the overturning circulation extend to the globe, so that the main conversion path is P M → K M → K E. This study shows that the LEC analyses improve the understanding of the atmospheric circulation on tidally locked terrestrial planets.

A molecular dynamics approach to investigate effect of pressure on asphaltene self-aggregation

Asphaltene aggregation is a serious issue in the oil industry that negatively affects the production, transportation, and exploitation of oil, causing considerable costs. In the past few years, the experimental analysis of asphaltene aggregation has been a fascinating topic; however, a laboratory study that can assess the asphaltene aggregation behaviors at high pressures will be a costly and high-risk project. In this paper, molecular dynamics (MD) simulations are used to investigate the influence of pressure on the asphaltene aggregation phenomenon. The employed asphaltene in this research is Gachsaran asphaltene (obtained from an Iranian oilfield) with archipelago geometry. The aggregation number, radial distribution function (RDF), potential of mean force (PMF), cohesive energy, solubility parameter, mean square displacement (MSD), diffusion coefficient, relative concentration, potential energy, and radius of gyration are analyzed based on the data and results obtained from the output trajectory files. It is concluded that the number and the average size of asphaltene aggregates significantly decrease with increasing pressure because the pressure delays the growth of asphaltene aggregates by enhancing the asphaltene solubility parameter. The associated energies of asphaltene molecules at 35, 90, and 135 bar are calculated to be −15.7834, −15.7571, and −15.7249 kJ / mol, respectively. It is found that the tendency of asphaltene molecules to aggregate reduces upon an increase in pressure. Face-to-face interactions are more likely than T-shaped and offset stacking for this asphaltene sample because of the more aromatic nuclei in the asphaltene structure than the aliphatic chains, which increase the strength of the π-π interactions. It is also observed that by increasing pressure, the movement and vibration of asphaltene increase and then decrease by further increase in pressure. According to the asphaltene onset envelope diagram, the asphaltene molecules at 35 bar are located in the solid–liquid region. As the pressure increases to 90 bar, the asphaltene passes the upper asphaltene onset point zone. It can be concluded that when asphaltene is in the solid–liquid region, the mobility and displacement of molecules increase with increasing pressure. In the upper asphaltene onset point zone, the tendency of molecules to move is reduced. The MD results are consistent with the laboratory data.

Tropical instability waves in a high-resolution oceanic and coupled GCM

Tropical instability waves (TIWs) are the dominant mesoscale variability in the eastern equatorial Pacific Ocean. TIWs have direct impacts on the local hydrology, biochemistry and atmospheric boundary layer, and feedback on ocean circulations and climate variability. In this study, the basic characteristics of Pacific Ocean TIWs simulated by an eddy-resolving ocean model and a coupled general circulation model are evaluated. The simulated TIW biases mainly result from the mean climatology state, as TIWs extract eddy energy from the mean potential and kinetic energy. Both the oceanic and coupled models reproduce the observed westward propagating large-scale Rossby waves between approximately 2°–8°N, but the simulated TIWs have shorter wavelengths than the observed waves due to the shallower thermocline. Meanwhile, the weak meridional shears of background zonal currents and the less-tilted pycnocline in these two models compared to the observations causes weak barotropic and baroclinic instability, which decreases the intensity of the simulated TIWs. We then contrast the TIWs from these two models and identify the roles of atmospheric feedback in modulating TIWs. The latent heat flux feedback is similar to observation in the coupled model but absent in the ocean model, contributing to the stronger standard deviation (STD) of the TIW SST in the ocean model. The ocean model is not able to capture realistic air–sea interaction processes when forced with prescribed atmospheric forcing. However, the misrepresented atmospheric feedback in the ocean model tends to decrease the sea surface height (SSH) variability, and the current feedback damping effect is stronger in the ocean model than in the coupled model. Combined with weaker barotropic conversion rate and baroclinic conversion rate in the ocean model than in the coupled model, the STD of the TIW SSH in the ocean model is weaker.

Variance of fluctuations from Noether invariance

The strength of fluctuations, as measured by their variance, is paramount in the quantitative description of a large class of physical systems, ranging from simple and complex liquids to active fluids and solids. Fluctuations originate from the irregular motion of thermal degrees of freedom and statistical mechanics facilitates their description. Here we demonstrate that fluctuations are constrained by the inherent symmetries of the given system. For particle-based classical many-body systems, Noether invariance at second order in the symmetry parameter leads to exact sum rules. These identities interrelate the global force variance with the mean potential energy curvature. Noether invariance is restored by an exact balance between these distinct mechanisms. The sum rules provide a practical guide for assessing and constructing theories, for ensuring self-consistency in simulation work, and for providing a systematic pathway to the theoretical quantification of fluctuations.

Molecular Simulation of the Effects of Cyclic Organic Compounds on the Stability of Lccbm Hydrates.

CH4 can be separated from low-concentration coal bed methane (LCCBM) by using the hydrate-based gas separation (HBGS) method. To study the contribution of different cyclic organic compounds to the separation of CH4 in LCCBM, an LCCBM hydrate model was constructed. Based on the Monte Carlo and molecular dynamics theory, we simulated the effect of three cyclic organic compounds—cyclopentane (CP), cyclopentanone (CP-one), and cyclopentanol (CP-ol)—on the stability of the LCCBM hydrate at P = 2 MPa, various temperatures, and discussed the structural stability of the hydrate in depth in terms of final snapshots, radial distribution function, mean square displacement, diffusion coefficient, and potential energy change. The results showed that for the CH4-N2 LCCMM gas mixture, CP showed the best facilitation effect compared to the other two cyclic compounds by maintaining the stability of the LCCBM hydrate well at T = 293 K. The promotion effect of CP-one is between CP and CP-ol, and when the temperature increases to T = 293 K, the oxygen atoms in the water molecule can maintain the essential stability of the hydrate structure, although the orderliness decreases significantly. Moreover, the structure of the hydrate model containing CP-ol is destroyed at T = 293 K, and the eventual escape of CH4 and N2 molecules in solution occurs as bubbles. The research results are important for further exploration of the mechanism of action of cyclic promoter molecules with LCCBM hydrate molecules and promoter preferences.

Seasonal Variation of Stratospheric Gravity Waves in the Asian Monsoon Region Derived from COSMIC-2 Data

COSMIC-2 (Constellation Observing System for Meteorology, Ionosphere and Climate- 2) dry temperature profile data from December 2019 to November 2021 are used to study stratospheric gravity waves (GWs) in the Asian monsoon region. The stratosphere between 20 and 50 km is divided into the lower, middle, and high layers based on the vertical distribution of the mean potential energy (Ep) and the horizontal distribution of GW Ep in these three layers, and their seasonal changes are analyzed. The source and propagating mechanism of GWs in middle latitudes in winter are revealed. The results show that GWs in the stratosphere have distinct distribution features during different seasons. The significant Ep in winter appears mainly in middle latitudes north of 30°N, whereas in summer, it appears in the low latitudes south of 30°N. There are significant areas of GW activity in both low and middle latitudes in spring and autumn, but their intensity is significantly weaker than in winter and summer. Areas with significant GWs and the seasonal variation of their intensity are accompanied by the Asian monsoon activity. In winter, there is a northward and upward propagating column for GWs above the Sichuan Basin, and in summer, there is an eastward and upward propagating column for GWs in the zonal band 15–25°N. The occurrence of GWs in northwestern China in winter is the result of the subtropical jet stream and topography. Once GWs enter the stratosphere, they are regulated by the winter stratospheric environment, and the GWs acquire a northerly component by the wind shear. The meridional wind shear in the background field is an important factor affecting the development and propagation of GWs.

Surface Divergent Eddy Heat Fluxes and Their Impacts on Mixed Layer Eddy‐Mean Flow Interactions

AbstractIn this study, the global surface divergent eddy heat flux (EHF) is estimated using remote sensing observations of sea surface height (SSH) and sea surface temperature (SST) over two decades (1993–2017). These results are used as a metric to assess model fidelity in a mesoscale eddy‐resolving version of the Community Earth System Model. The estimated EHFs show that the midlatitudes significantly contribute to the poleward transport of heat because of strong regional variability in SSH and SST. A Helmholtz decomposition is performed on the global EHFs to remove prominent nondynamic rotational wave‐like structures that appear in these fluxes. The dynamic divergent EHFs are responsible for driving cross‐frontal exchange and positive Baroclinic Conversion (BC) rates, suggesting a conversion of mean potential energy to eddy potential energy within the mixed layer. The results show that the model captures the same spatial patterns of EHFs and BC rates, but with relatively higher values in the midlatitudes than observations. The mixed layer geostrophic meridional eddy heat transport reaches maximums of 0.07 PW and 0.1 PW in the midlatitudes in the observations and climate model, respectively. The global integrated BC rate is 0.11 TW in the observations, which is ∼30% weaker than the climate model (0.16 TW). A cross‐spectral analysis further shows that the model has higher energy in low‐frequency bands for periods greater than 10 months in the northern hemisphere western boundary currents, but can capture the major spectral peaks in EHFs that are seen in observations.

Quantum counterpart of energy equipartition theorem for a dissipative charged magneto-oscillator: Effect of dissipation, memory, and magnetic field.

In this paper, we formulate and study the quantum counterpart of the energy equipartition theorem for a charged quantum particle moving in a harmonic potential in the presence of a uniform external magnetic field and linearly coupled to a passive quantum heat bath through coordinate variables. The bath is modeled as a collection of independent quantum harmonic oscillators. We derive closed form expressions for the mean kinetic and potential energies of the charged dissipative magneto-oscillator in the forms E_{k}=〈E_{k}〉 and E_{p}=〈E_{p}〉, respectively, where E_{k} and E_{p} denote the average kinetic and potential energies of individual thermostat oscillators. The net averaging is twofold; the first one is over the Gibbs canonical state for the thermostat, giving E_{k} and E_{p}, and the second one, denoted by 〈·〉, is over the frequencies ω of the bath oscillators which contribute to E_{k} and E_{p} according to probability distributions P_{k}(ω) and P_{p}(ω), respectively. The relationship of the present quantum version of the equipartition theorem with that of the fluctuation-dissipation theorem (within the linear-response theory framework) is also explored. Further, we investigate the influence of the external magnetic field and the effect of different dissipation processes through Gaussian decay and Drude and radiation bath spectral density functions on the typical properties of P_{k}(ω) and P_{p}(ω). Finally, the role of system-bath coupling strength and the memory effect is analyzed in the context of average kinetic and potential energies of the dissipative charged magneto-oscillator.

Atomistic simulation of the diffusion behavior in Al-Fe

• As Al block was attached to Fe block, Al atoms penetrated Fe block and vice versa on simulation. • Al atoms diffused massively into the Fe lattice, whereas Fe atoms moved deeper inside Al block. • The diffusion coefficient of Al was 2 times the diffusion coefficient of Fe. • Activation energy is 0.83 and 0.72 eV for Al and Fe, respectively. • Pre-exponentials is 1.03 × 10 −6 m 2 /s for Al and 5.83 × 10 −8 m 2 /s for Fe. The diffusion behavior of the Al-Fe system was investigated by a classical molecular dynamics simulation for simulating the Al coating process on Fe. Two bulks were built as the model: one bulk contained Al atoms and the other was made from Fe atoms. The diffusion was studied at four different temperatures for 6 ns by utilizing a MEAM potential. The mean square displacement (MSD) and potential energy of Al and Fe atoms were recorded during the simulation. Fe atoms penetrated inside the Al lattice in low quantities and at a slower rate compared with the fast and large number of diffusing Al atoms that did not penetrate inside the Fe lattice. The diffusion coefficient was estimated by the fitting of the linear region from the MSD and time curves. The Arrhenius equation was used to find the activation energy and the frequency of attempts. The activation energy of Al was 0.83 eV, whereas that of Fe was 0.72 eV. The frequency of attempts for the Al and Fe atoms were 1.03 × 10 - 6 and 5.83 × 10 - 8 m 2 /s, respectively. The diffusing mechanisms were studied, and it was found that the Fe atoms diffused into the Al lattice by the first-neighbor hopping mechanism. The potential energy of the Fe atoms increased as the Fe atoms penetrated the Al lattice.

On two approaches to the third-order solution of surface gravity waves

A third-order approximate solution for surface gravity waves in the finite water depth is studied in the context of potential flow theory. This solution corresponds to the steady-state part of a multidirectional irregular wave field and provides explicit expressions for the surface elevation, free-surface velocity potential, and velocity potential. The amplitude dispersion relation is also provided. Two approaches are used to derive the third-order analytical solution, resulting in two types of approximate solutions: the perturbation solution and the Hamiltonian solution. The perturbation solution is obtained by a classical perturbation technique in which the time variable is expanded in multiscale to eliminate secular terms. The Hamiltonian solution is derived from the canonical transformation in the Hamiltonian theory of water waves. By comparing the two types of solutions, it is found that they are completely equivalent for the first- and second-order solutions and the nonlinear dispersion, but for the third-order part only the sum–sum terms are the same. Due to the canonical transformation that could completely separate the dynamic and bound harmonics, the Hamiltonian solutions break through the difficulty that the perturbation theory breaks down due to singularities in the transfer functions when the quartet resonance criterion is satisfied. Furthermore, it is also found that some time-averaged quantities based on the Hamiltonian solution, such as mean potential energy and mean kinetic energy, are equal to those in the initial state in which the sea surface is assumed to be a Gaussian random process. This is because there are associated conserved quantities in the Hamiltonian form. All of these show that the Hamiltonian solution is more reasonable and accurate to describe the third-order steady-state wave field. Finally, based on the Hamiltonian solution, some statistics are given such as the volume flux, skewness, excess kurtosis, and non-uniqueness of the induced mean flow and mean surface.

The Role of Tropical, Midlatitude, and Polar Cloud-Radiative Changes for the Midlatitude Circulation Response to Global Warming

AbstractPrevious studies showed that global cloud-radiative changes contribute half or more to the midlatitude atmospheric circulation response to global warming. Here, we investigate the relative importance of tropical, midlatitude, and polar cloud-radiative changes for the annual-mean, wintertime, and summertime circulation response across regions in AMIP-like simulations. To this end, we study global warming simulations from the ICON model run with the cloud-locking method and prescribed sea surface temperatures, which isolate the impact of changes in atmospheric cloud-radiative heating. Tropical cloud changes dominate the global cloud impact on the 850 hPa zonal wind, jet strength, and storm track responses across most seasons and regions. For the jet shift, a more diverse picture is found. In the annual mean and DJF, tropical and midlatitude cloud changes contribute substantially to the poleward jet shift in all regions. The poleward jet shift is further supported by polar cloud changes across the Northern Hemisphere but not in the Southern Hemisphere. In JJA, the impact of regional cloud changes on the jet position is small, consistent with an overall small jet shift during this season. The jet shift can be largely understood via the anomalous atmospheric cloud-radiative heating in the tropical and midlatitude upper troposphere. The circulation changes are broadly consistent with the influence of cloud-radiative changes on upper-tropospheric baroclinicity and thus the mean potential energy available for conversion into eddy kinetic energy. Our results help to explain the jet response to global warming and highlight the importance of tropical and midlatitude cloud-radiative changes for this response.

Norwegian Atlantic Slope Current along the Lofoten Escarpment

Abstract. Observations from moored instruments are analyzed to describe the Norwegian Atlantic Slope Current at the Lofoten Escarpment (13∘ E, 69∘ N). The data set covers a 14-month period from June 2016 to September 2017 and resolves the core of the current from 200 to 650 m depth between the 650 and 1500 m isobaths. The along-isobath current, vertically averaged between 200 and 600 m depth, has an annual cycle amplitude of 0.1 m s−1, with the strongest currents in winter, and a temporal average of 0.15 m s−1. Higher-frequency variability is characterized by fluctuations that reach 0.8 m s−1, lasting for 1 to 2 weeks, and extend as deep as 600 m. In contrast to observations in Svinøy (2∘ E, 63∘ N), the slope current is not barotropic and varies strongly with depth (a shear of 0.05 to 0.1 m s−1 per 100 m in all seasons). Within the limitations of the data, the average volume transport of Atlantic Water is estimated at 2.0±0.8 Sv (1 Sv =106 m3 s−1), with summer and winter averages of 1.6 and 2.9 Sv, respectively. The largest transport is associated with the high temperature classes (>7 ∘C) in all seasons, with the largest values of both transport and temperature in winter. Calculations of the barotropic and baroclinic conversion rates using the moorings are supplemented by results from a high-resolution numerical model. While the conversion from mean to eddy kinetic energy (e.g., barotropic instability) is likely negligible over the Lofoten Escarpment, the baroclinic conversion from mean potential energy into eddy kinetic energy (e.g., baroclinic instability) can be substantial, with volume-averaged values of (1–2)×10-4 W m−3.