Adiabatic Heating Research Articles

Impacts of the extratropical North Pacific on boreal summer Arctic circulation

A distinct characteristic of the Arctic summer atmospheric circulation is the anomalous anticyclonic circulation centered over the Arctic Ocean associated with significant Arctic warming. Previous studies have related the underlying mechanisms to the earlier spring Eurasian snowmelt and the tropical Pacific forcing. Here, the authors show that the Arctic summer anomalous anticyclonic circulation is significantly related to the extratropical North Pacific sea surface temperature anomalies (SSTAs) in spring, indicating a teleconnection from the extratropical North Pacific to the Arctic. The SSTA pattern is characterized by warm anomalies in the midlatitudes of the extratropical North Pacific surrounded by significant cold anomalies, resembling the negative phase of the Pacific Decadal Oscillation (PDO) but without significant signals in the tropics (referred to as the negative PDO-like pattern). This negative PDO-like pattern in May can stimulate a Rossby wave propagating from the Bering Sea to the Arctic and lead to an anomalous Arctic anticyclone which can be sustained during summer. Meanwhile, the negative PDO-like pattern can persist to summer and induce an anomalous surface low pressure over the Bering Sea in summer. This anomalous surface low causes anomalous rising motions and induces upper-level divergence anomalies which further intensify the summer Arctic anticyclone. The upper-level tropospheric Arctic anticyclone can force anomalous adiabatic descent over the Arctic and sub-Arctic, leading to significant adiabatic heating in the Arctic. As a result, a significant warming emerges over the Arctic with the center located in the middle troposphere. The connection between the negative PDO-like SSTAs and the summer Arctic anticyclone has been confirmed by numerical experiments.

Dynamics of Thermospheric Traveling Atmospheric Disturbance During a Geomagnetic Storm

AbstractTraveling atmospheric disturbance (TAD) plays an important role in the energy and momentum transfer from the lower atmosphere to the upper atmosphere, and from high‐ to low‐latitudes. It is common to observe TADs propagating toward low latitudes because of enhanced Joule heating and/or the Lorentz force at the high‐latitude ionosphere during storm time. However, energy or momentum variation associated with their equatorward propagation remains unclear. Two geomagnetic storms occurred on 7–8 September 2017 and upper atmospheric disturbances are observed by the Swarm satellites and the Global Navigation Satellite System Total Electron Content network. We conduct a model simulation and term analysis of the energy equation to investigate the dominant terms of TAD. Adiabatic heating, conduction heating, and advection heating dominate the energy budget of TAD. Adiabatic heating plays an important role in the energy budget by transferring the most energy of TAD. An anti‐phase relationship between adiabatic and conduction heating is found in the propagation of these TADs. An in‐phase relationship between adiabatic and advection heating is also found. Physical processes behind these anti‐phase and in‐phase relationships are illustrated with a schematic. Finally, based on the dominant terms and the relationships between them, the whole process of generation, propagation, and dissipation of TAD is given.

Observation of subcritical shocks in a collisional laboratory plasma: scale dependence near the resistive length

We present a study of subcritical shocks in a highly collisional laboratory plasma with a dynamically significant magnetic field. Shocks were produced by placing cylindrical obstacles into the supermagnetosonic ( $M_{{\rm MS}} \sim 1.9$ ) outflow from an inverse wire array z-pinch at the MAGPIE pulsed power facility ( $n_{e} \sim 8.5 \times 10^{17}\,{\rm cm}^{-3}$ , $v \sim 45\,{\rm km}\,{\rm s}^{-1}$ ). We demonstrate the existence of subcritical shocks in this regime and find that secondary stagnation shocks form in the downstream which we infer from interferometry and optical Thomson scattering measurements are hydrodynamic in nature. The subcritical shock width is found to be approximately equal to the resistive diffusion length and we demonstrate the absence of a jump in hydrodynamic parameters. Temperature measurements by collective optical Thomson scattering showed little temperature change across the subcritical shock ( ${<}10\,\%$ of the ion kinetic energy) which is consistent with a balance between adiabatic and Ohmic heating and radiative cooling. We demonstrate the absence of subcritical shocks when the obstacle diameter is less than the resistive diffusion length due to decoupling of the magnetic field from the plasma. These findings are supported by magnetohydrodynamic simulations using the Gorgon and AstroBEAR codes and discrepancies between the simulations and experiment are discussed.

Erratum: “Comprehensive characterization of the adiabatic temperature change and (convection) heat transfer coefficient of a NiTi tube elastocaloric refrigerant” [AIP Adv. 13, 065202 (2023)

Erratum: “Comprehensive characterization of the adiabatic temperature change and (convection) heat transfer coefficient of a NiTi tube elastocaloric refrigerant” [AIP Adv. 13, 065202 (2023)

On the use of an induced temperature gradient and full‐field measurements to investigate and model the thermomechanical behaviour of an austenitic stainless steel 316

AbstractA temperature gradient was induced in 316 stable austenitic stainless‐steel tension specimens, and the strain and temperature evolution during tensile deformation was monitored using optical and infrared cameras. The combination of global load with full‐field strain and temperature provided local information on the thermomechanical state of the investigated material. The deformation did not fully concentrate on the hotter portion of the specimen, but instead, the hottest portion strain hardened enough so that the colder portions of the specimen also experienced plastic deformation. Evidently, heat release occurred with plastic deformation and altered the initial temperature gradient as deformation progressed. The Taylor–Quinney coefficient was computed in integral and differential forms, and both are presented as a function of temperature and strain. The Johnson–Cook plasticity model was calibrated through an inverse method procedure in which only five tests were used, and the obtained temperature and strain rate dependencies of the model were comparable to those found in the literature for the same material. A local analysis was done to quantify the impact of adiabatic heating on the mechanical behaviour of the material.

Numerical analysis of transient heat and mass transfer for a water heat pipe under non-uniform heating conditions

Non-uniform loads are widely present in heat pipe applications and have significant effects on their performance. In this work, a transient 3D CFD model is developed to investigate the liquid–vapor flow and heat transfer for a water heat pipe under various non-uniform loads. The source terms are added to the governing equations using the User-Defined Function (UDF) to simulate the evaporation and condensation process. The model is verified using the experimental and simulated data under uniform and non-uniform loads in the literature. The effects of key parameters including adiabatic length, heating power, and heat distribution on the thermal performance of heat pipes are analyzed. The results show that the non-uniform conditions would shift the maximum axial velocity of vapor to the unheated side and induce a significant circumferential flow in the wick region, especially in the evaporator section. The short adiabatic length and high heating power could reduce the elapsed time of reaching the steady state. The heat distribution in the evaporator section exhibits little effect on the elapsed time reaching the steady-state and the average steady-state vapor temperature

Spherical cavity expansion method dependent on strain, strain rate, and temperature

This paper presents a spherical cavity expansion method based on the self-similar field considering dynamic hardening, which includes plastic strain, plastic strain rate, and temperature for an infinite compressible medium under J2 plasticity. This study proposes an approach based on the gradients of plastic strain and temperature under self-similarity transformation to deal with dynamic hardening models such as the Johnson-Cook (JC) and the modified Johnson-Cook (mJC) models. A theoretical model shows that the effective and radial stresses are reduced near the cavity surface and increased away from the cavity under the mutual influence of hardening and thermal softening. The JC hardening model is used to analyze the behavior of the cavity expansion for AISI 4340 steel. The proposed theoretical model was validated by comparing the result of the explicit finite element method (FEM). This study discusses the behavior of the expanding cavity problem for thermal softening and strain rate sensitivities. In addition, rigid penetration problems are simulated to analyze the application of the presented method. FEM and the proposed cavity expansion method were compared with the penetration depth of AA6061-T651 target using the mJC hardening model for a hemispherical-nosed penetrator. A comparison is made for the performance of the penetration depth with an ogive-nose projectile for AA7075-T651 and AA6061-T651 materials using the mJC hardening model. This study concludes that the proposed method can be applied without modifying the hardening models to spherical cavity expansion problems that involve dynamic hardening models dependent on strain, strain rate, and temperature under adiabatic heat.

Effect of Microchannel on the Composite Cooling Performance of a Simulated Turbine Blade Leading Edge

Abstract As the turbine blade leading edge becomes one of the hottest regions in the engine, a microchannel structure was applied to further improve the cooling performance. Adiabatic and conjugate heat transfer analyses were conducted to compare the heat transfer and cooling performance of the leading edge with or without microchannels, while the influence of mass flowrate of coolant was also included. Based on the investigations on the effect of geometrical designs, the flow and composite cooling performance of the microchannels were further optimized. The results indicate that the internal heat transfer intensity was greatly enhanced with the arrangement of microchannels, while the adiabatic film coolant coverage was slightly deteriorated. On this basis, the composite cooling performance of the leading edge was effectively improved by at least 7.54%. However, the flow resistance of film cooling holes was obviously increased due to the obstruction of microchannels, and a larger thickness of microchannels would alleviate this feature. In addition, the composite cooling performance of the leading edge was further optimized by increasing the radius of microchannels, and the same effect was achieved by reducing the spanwise distance between the film cooling holes and the microjet holes. Compared with the leading edge model without microchannels, the former design increased the area-averaged overall cooling effectiveness of the leading edge by at least 11.17% under all the mass flow rates of coolant studied in this paper, while the latter design improved the composite cooling performance by at least 12.76%.

High-Pressure Processing of Human Milk: A Balance between Microbial Inactivation and Bioactive Protein Preservation

BackgroundDonor human milk banks use Holder pasteurization (HoP; 62.5°C, 30 min) to reduce pathogens in donor human milk, but this process damages some bioactive milk proteins. ObjectivesWe aimed to determine minimal parameters for high-pressure processing (HPP) to achieve >5-log reductions of relevant bacteria in human milk and how these parameters affect an array of bioactive proteins. MethodsPooled raw human milk inoculated with relevant pathogens (Enterococcus faecium, Staphylococcus aureus, Listeria monocytogenes, Cronobacter sakazakii) or microbial quality indicators (Bacillus subtilis and Paenibacillus spp. spores) at 7 log CFU/mL was processed at 300–500 MPa at 16–19°C (due to adiabatic heating) for 1–9 min. Surviving microbes were enumerated using standard plate counting methods. For raw milk, and HPP-treated and HoP-treated milk, the immunoreactivity of an array of bioactive proteins was assessed via ELISA and the activity of bile salt-stimulated lipase (BSSL) was determined via a colorimetric substrate assay. ResultsTreatment at 500 MPa for 9 min resulted in >5-log reductions of all vegetative bacteria, but <1-log reduction in B. subtilis and Paenibacillus spores. HoP decreased immunoglobulin A (IgA), immunoglobulin M (IgM), immunoglobulin G, lactoferrin, elastase and polymeric immunoglobulin receptor (PIGR) concentrations, and BSSL activity. The treatment at 500 MPa for 9 min preserved more IgA, IgM, elastase, lactoferrin, PIGR, and BSSL than HoP. HoP and HPP treatments up to 500 MPa for 9 min caused no losses in osteopontin, lysozyme, α-lactalbumin and vascular endothelial growth factor. ConclusionCompared with HoP, HPP at 500 MPa for 9 min provides >5-log reduction of tested vegetative neonatal pathogens with improved retention of IgA, IgM, lactoferrin, elastase, PIGR, and BSSL in human milk.

Prediction of ionic conductivity from adiabatic heating in non-equilibrium molecular dynamics on various test systems.

The evaluation of ionic conductivity through atomistic modeling typically involves calculating diffusion coefficients, which often necessitates simulations spanning several hundreds of nanoseconds. This study introduces a less computationally demanding approach based on non-equilibrium molecular dynamics applicable to a wide range of systems. Ionic conductivity is determined by evaluating the Joule heating effect recorded during non-equilibrium molecular dynamics (NEMD) simulations. These simulations which involve applying a uniform electric field using classical force fields in LAMMPS are conducted within the MedeA software environment. The conductivity value for a specific temperature can thus be obtained from a single simulation together with an estimation of the associated uncertainty. Guidelines for selecting NEMD parameters such as electric field intensity and initial temperature are proposed to satisfy linear irreversible transport. The protocol presented in this study is applied to four different types of systems, namely, (i) molten NaCl, (ii) NaCl and LiCl aqueous solutions, (iii) solution of ionic liquid with two solvents, and (iv) NaX zeolites in the anhydrous and hydrated states. The main advantages of the proposed protocol are simplicity of implementation (eliminating the need to store individual ion trajectories), reliability (low electric field, linear response, no perturbation of the equations of motion by a thermostat), and a wide range of applications. The estimated contribution of field-induced drift motion of ions to kinetic energy appears very low, justifying the use of standard kinetic energy in the method. For each system, the reported influence of temperature, ion concentration, solvent nature, or hydration is correctly predicted.

Synoptic characteristics of heatwave events in Australia during austral summer of 1950/1951–2019/2020

AbstractAustralia has experienced increasing number of heatwave events (HWEs) in recent decades. This study aims to examine key synoptic features of austral summer HWEs over Australia during 1950/1951–2019/2020. Based on ERA5‐reanalysis and rotated empirical orthogonal functions, HWEs in Australia are categorized into four types according to where they often occur together: East Australia (EA), North Australia (NA), West Australia (WA) and Southeast Australia (SEA). Our results reveal that while anomalous anticyclones at 500 hPa level are the typical synoptic circulations responsible for HWEs of each subregion, their specific mechanisms differ between subregions. The atmospheric heat budget at 850 hPa level shows that anomalous diabatic heating promotes the onset of HWEs in each subregion. While anomalous vertical advection and adiabatic heating due to the anomalous subsidence play an important role in maintaining HWEs till their demise in NA, they only help trigger HWEs in EA, SEA and WA. Our results also suggest that anomalous advection of climatological mean temperature is important to both the onset and persistence of HWEs in EA and SEA, while it only helps sustain (trigger) HWEs in NA (WA). The advection of anomalous temperature also acts to trigger HWEs in EA, SEA and WA. On the surface, upward long‐wave radiation and sensible heat flux contribute to the development of HWEs, whereas both of them are reduced in SEA due to the enhanced anomalous cyclones near the surface and the decreased land–air temperature difference. These findings help improve understanding of the synoptic characteristics and distinctive mechanisms of HWEs in different subregions of Australia.

Dynamic and thermodynamic causes of summer extreme precipitation over South China

The summer days between 1961 and 2017 are divided into two categories: extreme precipitation days (EPDs) and general precipitation days (GPDs). Compared to GPDs, on EPDs, South China (SC) is affected by a local trough in the lower troposphere and the East Asian subtropical westerly jet (EAWJ) is strengthened in the upper troposphere. The anomalous extension of the western Pacific subtropical high (WPSH) in the South China Sea (SCS) is a key of EPDs. The reason for the extension of WPSH is due to a Kelvin wave-induced Ekman divergence (WIED) response to the SST anomaly zonal contrast between the tropical Indian Ocean (TIO) and tropical Pacific Ocean (TPO). The vertical velocity gradient ∂ω/∂p anomaly in accord with Sverdrup vorticity balance plays a secondary reinforcing role. Utilizing the quasi-geostrophic omega (QG ω) equation, the quantitative contributions of the dynamic term ωD and thermodynamic term ωQ are examined. On EPDs, the ωQ term over SC has the largest contribution to total ω, accounting for 46.2%, while the ωD term accounts for only 16.7%. The variation of ωQ is the main contributor to the variation of ω within different precipitation ranges, with time and with vertical levels. Water vapor plays a crucial role in adiabatic heating. The moisture budget analysis suggests that water vapor transport is significantly converted into precipitable water from 3 days before EPDs, increasing the humidity of the atmosphere and providing favorable conditions for adiabatic heating.

Investigation on the suppression effect of high momentum C6F12O (Novec-1230) flow on hydrogen jet flame

This work investigates the suppression effect of Novec-1230 on H2 jet flame. The suppressants are motivated by N2 flow to get higher momentum and approach the reaction kernel at flame base. The flame area with Novec-1230 is always smaller than that with water mist at the same condition. Novec-1230 exhibits better suppression effect on reaction kernel. The higher-momentum jet flame is more difficult to be suppressed. This is because that the higher-momentum flame makes the suppressant approach the reaction kernel more difficult. In addition, the high N2 flow rate containing suppressant could destroy flame temperature structure and decrease it. Results inferred that the temperature of flame with Novec-1230 is higher than that with water mist. Moreover, the lower minimum extinguishing time indicates that the suppression efficiency of Novec-1230 is better than that of water mist. The jet flame is extinguished only when H2 flow rate is low and N2 flow rate is high. There are two reasons: one is that the higher-momentum jet flame prevents suppressants to enter flame core. The other one is that the burner nozzle is heated to as igniting source during suppression progress. Furthermore, the burning velocity, adiabatic flame temperature, heat production and free radicals are investigated theoretically at Φ = 1.6, 1.0, 0.8 and 0.6. Results indicate that the burning velocity with Novec-1230 is much lower than that with water mist. The adiabatic flame temperature, heat production and free radicals increase firstly and then decrease with Novec-1230 addition at lean flame.

Significance of adiabatic heating on phase transformation in titanium-based alloys during severe plastic deformation

Experiments were conducted on Ti-based alloys including a commercially pure titanium (α phase), Ti-6Al-4 V (α + β phase) and TiNi (B19’-martensitic phase) alloys in order to investigate the phase transformation during high-pressure torsion (HPT) at room temperature. An allotropic α to ω phase transformation in the commercially pure titanium occurred during HPT processing but increasing the rotation speed led to a decrease in the volume fraction of the ω-phase. This procedure facilitates the loss of the β phase in the Ti-6Al-4 V alloy and promotes a B19’ to B2 (austenite) phase transformation in the TiNi alloy. The results show that the bulk temperature increment in the processed specimens was not sufficiently high to affect phase transformations. However, the calculations by assuming adiabatic conditions revealed that the local temperature increment is responsible to encourage or suppress the phase transformation in the Ti-based alloys. This fundamental understanding of phase transformations during severe plastic deformation is useful for conducting microstructure engineering of Ti-based alloys by tailoring the microstructures containing different phases and thereby producing different mechanical and functional behaviors.

Dynamic recrystallization during hot compression of Ni-based superalloy Haynes 282

Understanding the microstructural behaviour of materials during thermomechanical processing is a vital step towards optimizing the mechanical properties. One important aspect during forming processes, such as forging, is dynamic recrystallization (DRX), which sets the starting microstructure for the subsequent manufacturing steps. Here we investigated the DRX behaviour of Ni-base superalloy Haynes 282 during hot compression with a strain rate of 0.05 s−1 at 1080 °C, with care taken to minimize the effects of meta-dynamic recrystallization (mDRX) and adiabatic heating. Small DRX grains could be observed already at ε = 0.1, i.e. before the peak strain εp = 0.15. The DRX process accelerated significantly above ε = 0.2, and the material was fully recrystallized at ε = 1.5. Up to ε = 0.8 DRX occurred through continuous nucleation of new grains, whereas above ε = 0.8 the number density of DRX grains decreased and the increase in recrystallized fraction was due to growth of existing grains. Contrary to common assumptions of DRX nuclei being essentially dislocation free, many of the DRX grains contained pronounced dislocation substructures, even at small strains where they are not expected to have undergone deformation.

Numerical Simulation of the Effect of Heat Conductivity on Proton Exchange Membrane Fuel Cell Performance in Different Axis Directions

In this paper, the effect of changes in the thermal conductivity of porous electrodes in three coordinate directions on the capability of proton exchange membrane fuel cells is investigated on the basis of current density versus voltammetry curves, and the temperature distribution and water-carrying capacity distribution of the membrane. The results show that when the cell discharge voltage of the PEMFC is 0.3 V, the thermal conductivity in the Z-direction of the porous electrode has a greater effect on the performance of the PEMFC than in the other directions, with the thermal conductivity in the X- and Y-directions of the porous electrode having less than a 5% effect on the performance of the PEMFC, which can therefore be neglected. When the thermal conductivity of the porous electrode in the Z-direction of the PEMFC is 500 W/(m·K) and 1000 W/(m·K), the performance of the PEMFC is improved by 5.78% and 5.87%, respectively, and when the thermal conductivity of the porous electrode in the X-direction of the PEMFC is 500 W/(m·K) and 1000 W/(m·K), the performance of the PEMFC is improved by 2.09% and 2.89%, and the PEMFC performance is improved by 1.51% and 2.00% when the Y-direction thermal conductivity of the porous electrode of the PEMFC is 500 W/(m·K) and 1000 W/(m·K), respectively. The improvement in performance decreases with increasing thermal conductivity, because the thickness of the porous electrode is too thin. Since the side of the model is set to adiabatic heat exchange conditions, while the top and bottom surfaces are set to natural convection heat exchange conditions, the Z-direction thermal conductivity of the porous electrode plays the most important role in the temperature distribution of the PEMFC. The Z-direction thermal conductivity of the porous electrode causes the temperature distribution of the PEMFC assembly to be more uniform, and the Z-direction thermal conductivity of the porous electrode also causes the area of the high-water-content region on the proton exchange membrane to significantly increase.

Comprehensive characterization of the adiabatic temperature change and (convection) heat transfer coefficient of a NiTi tube elastocaloric refrigerant

Elastocaloric cooling without global warming substance emission is a promising alternative to the vapor-compression technology. Comprehensive and precise characterization of the adiabatic temperature change of the elastocaloric refrigerant and the heat transfer coefficient between the elastocaloric refrigerant and the surrounding heat transfer fluid/solid is significant for the structural design of elastocaloric coolers. In this article, an analytical solution of the volume-averaged temperature variation in a tubular shape memory alloy elastocaloric refrigerant under cyclic compression was derived using lumped analysis, and a method of comprehensive characterization of the adiabatic temperature change (∆Tad) and (convection) heat transfer coefficient h for the elastocaloric refrigerant based on the analytical solution was proposed. A dimensionless number Ch was defined as the ratio of the latent heat release/absorption rate to the (convection) heat transfer rate, with which the characterization procedure including a series of nonlinear least-square regression tests and data selection criteria were established. The method proposed is applicable to any cross section geometry under both tension and compression, and it was validated using experimental data on a NiTi tube under sinusoidal force-controlled and reverse Brayton cyclic compressions and using existing experimental data of NiTi-based films, strips, and pillars under tension and compression in the literature. The ∆Tad characterized using the proposed method agreed with that using the reverse Brayton cyclic loading method within 5% (absolute value of 1 K). The effect of data selection sequence on the characterization of ∆Tad and h was investigated, and the results showed that proper starting points were significant for the convergence of ∆Tad and h.

Constitutive modeling for elevated temperature flow behavior of a novel Cr-Si alloyed hot stamping steel

The flow behavior of a novel Cr-Si alloyed hot stamping steel (Cr-Si steel) at elevated temperature was investigated via isothermal compression tests on a Gleeble-3500 thermomechanical simulator with a temperature range of 600 ∼ 900 °C and a strain rate range of 0.1 ∼ 10 s−1. Subsequently, the Arrhenius-type constitutive model, comprising strain compensation, was established in accordance with the friction and adiabatic heating corrected stress-strain curves. Furthermore, the predictability and prediction accuracy of the constitutive model were verified. The results reveal that at a constant strain rate, the flow stress of the Cr-Si steel initially increases as the strain increases before tending to stabilize, owning to the combined effects of work hardening and dynamic recovery. The peak flow stresses decrease as the temperatures increase and the strain rates decrease. The constitutive model can accurately predict the elevated temperature constitutive relationship of the Cr-Si steel during the hot stamping process.

State and evolution of the geodynamo from numerical models reaching the physical conditions of Earth’s core

SUMMARY Our understanding of the geodynamo has recently progressed thanks to geomagnetic data of improved quality, and analyses resting on numerical simulations of increasing realism. Here, these two advances are combined in order to diagnose the state and present dynamics of Earth’s core in physically realistic conditions. A sequential, ensemble-based framework assimilates the output of geomagnetic field models covering the past 180 yr into a numerical geodynamo simulation, the physical realism of which is also advanced as data is assimilated. The internal dynamical structure estimated for the geodynamo at present reproduces previously widely documented features such as a planetary-scale, eccentric westwards gyre and localization of buoyancy release beneath the Eastern (0°E−180°E) hemisphere. Relating the typical magnetic variation timescale of the assimilated states to the power at which they operate, the present convective power of the geodynamo is estimated at 2.95 ± 0.2 TW, corresponding to an adiabatic heat flow out of the core of 14.8 ± 1 TW if the top of the core is convectively neutrally stratified at present. For the first time, morphologically and dynamically relevant trajectories are obtained by integrating the estimated states forward for a few decades of physical time using a model reaching the physical conditions of Earth’s core. Such simulations accurately account for the spatio-temporal content of high-resolution satellite geomagnetic field models and confirm earlier interpretations in terms of rapid core dynamics. The enforcement of a realistic force balance approaching a Taylor state allows for propagation of weak (velocity perturbation of about 0.6 $\mathrm{km\,yr^{-1}}$) axisymmetric torsional waves with period about 5 yr, supported by a magnetic field of root-mean-squared amplitude of 5.6 mT inside the core. Quasi-geostrophic magneto-Coriolis waves of interannual periods and significantly stronger velocity perturbation (about $7 \mathrm{km\,yr^{-1}}$) are also reproduced, with properties that converge towards those recently retrieved from the analysis of geomagnetic variations before fully achieving Earth’s core conditions. The power spectral density of magnetic variations falls off rapidly at frequencies exceeding the inverse Alfvén time (about $0.6\mathrm{yr^{-1}}$), which indicates that the excitation of hydromagnetic waves occurs preferentially at large spatial scales. The possibility to account for geomagnetic variations from years to centuries in physically realistic models opens the perspective of better constraining properties of the deep Earth through geomagnetic data assimilation.

The onset of stratospheric final warming and record–breaking April surface warming over Central Asia in 2022

In the spring of 2022, a stratospheric final warming (SFW) event occurred on March 19 at 10 hPa in the Northern Hemisphere, ranking the third earliest SFW event during 1979–2022. Meanwhile, Central Asia recorded the highest surface air temperature (SAT) in the ensuing April in recent 44 years. Based on the fifth generation reanalysis data from European Centre for Medium-Range Weather Forecasts, this study reports an intimate linkage between the SFW onset and the extremely high SAT in Central Asia in April 2022. Specifically, after the SFW onset, positive geopotential height anomalies in the stratospheric polar region persist for more than a month, which propagate downward to the troposphere in about one week, resulting in a negative phase of the Northern Annular Mode (NAM) in the upper troposphere during the period from late March to mid-April. Such a negative NAM tends to excite an anomalous Rossby wave train propagating southeastward from the North Atlantic to Central Asia, causing an anomalous high over Central Asia in the middle and upper troposphere. As a result, the associated anomalies in descending motion and adiabatic heating would lead to the in situ unprecedented high SAT in April.