Variable Temperature Gradient Research Articles

Energy conversion performance in looped and stirling traveling-wave and standing-wave thermoacoustic engines

This present study conducts a comprehensive comparison of looped traveling-wave thermoacoustic engines (TWTAEs) and Stirling TWTAEs using two- and three-dimensional (2D and 3D) time-domain models. These models, validated through comparisons with existing experimental results, confirm the accuracy of our developed full-scale numerical TWTAE models. By evaluating the acoustic characteristics and comparing them with conventional standing-wave thermoacoustic engines, this work highlights the superior performance of the Stirling TWTAE. It achieves the highest heat-driven acoustic power and thermoacoustic energy conversion efficiency. This superior performance is attributed to its operation at a lower oscillation frequency (115 Hz) and an optimized phase between acoustic velocity and pressure oscillations (40 degrees). Additionally, our study explores rich nonlinear phenomena within the flow fields of the Stirling TWTAE. Notably, varying the temperature gradients between 410 K and 485 K introduces a bistable zone with distinct pressure amplitudes. Moreover, mass streaming under varying temperature gradients, and mode transitions due to external flow perturbations are observed inside the engine. These findings not only quantitatively confirm the high efficiency potential of the Stirling TWTAE but also demonstrate the effectiveness of CFD in the development of full-scale numerical models for predicting and optimizing the heat-driven acoustic characteristics and nonlinear phenomena of traveling-wave thermoacoustic systems.

Experimental analysis of the synergistic impact of fan and nocturnal thermal insulation on enhancing the thermal performance of latent-energy-storage solar air collectors

Solar air collectors equipped with energy storage functionality are widely utilized to address the mismatch between heat demand and supply periods during winter, effectively facilitating heating needs. However, phase change energy storage flat plate solar air collectors are hindered by inefficiencies, primarily due to the low rate of convective heat transfer and substantial nocturnal energy losses, which considerably undermine the overall energy efficiency of these collectors. In response to these challenges, a forced convection approach utilizing a fan was adopted to augment the convective heat transfer rate, and insulation was applied to glass panes overnight to curb energy wastage. Two solar air collector systems were constructed and examined: a natural convection-based energy storage solar air collector (NCSAC-PCM) and another solar air collector incorporating forced convection with nocturnal thermal insulation (FCSAC-PCM-NTI). Comparative experiments revealed that the combination of forced convection with nighttime insulation in the latter design led to an elevation in the mean indoor temperature by 1.4 °C, alongside a decrease in the temperature gradient variation within the space during the test period. Furthermore, this integration significantly enhanced the energy efficiency by 53.71 % and the exergy efficiency by 11.45 %.

Solar Heating Modulated by Evaporative Cooling Provides Intermittent Temperature Gradients for Ionic Thermoelectric Supercapacitors

AbstractSolar heating is important for many applications but less attractive for concepts requiring intermittent heating, such as ionic thermoelectric supercapacitors (ITESCs). However, the heating process even at constant solar illumination can be converted to temperature oscillations through water infiltration and evaporation. Here, this process is demonstrated for a carbon nanotube‐cellulose membrane and used to induce temporally varying temperature gradients across an ITESC, which enables continuous operation through repeated charge and discharge cycles. A temperature variation of 10 K can be generated on the top electrode, which leads to a variation in the temperature difference across the ITESC of 7.5 K. Precise control over charge and discharge durations can be achieved by adjusting the volume and interval of the added water. The concept of temporarily adjusting temperatures by evaporative cooling may be extended to create intermittent heating also for other heat sources that are typically constant.

Early Warning for Continuous Rigid Frame Bridges Based on Nonlinear Modeling for Temperature-Induced Deflection.

Bridge early warning based on structural health monitoring (SHM) system is of significant importance for ensuring bridge safe operation. The temperature-induced deflection (TID) is a sensitive indicator for performance degradation of continuous rigid frame bridges, but the time-lag effect makes it challenging to predict the TID accurately. A bridge early warning method based on nonlinear modeling for the TID is proposed in this article. Firstly, the SHM data of temperature and deflection of a continuous rigid frame bridge are analyzed to examine the temperature gradient variation patterns. Kernel principal component analysis (KPCA) is used to extract principal temperature components. Then, the TID is extracted through wavelet transform, and a nonlinear modeling method for the TID considering the temperature gradient is proposed using the support vector machine (SVM). Finally, the prediction errors of the KPCA-SVM algorithm are analyzed, and the early warning thresholds are determined based on the statistical patterns of the errors. The results show that the KPCA-SVM algorithm achieves high-precision nonlinear modeling for the TID while significantly reducing the computational load. The prediction results have coefficients of determination above 0.98 and fluctuate within a small range with clear statistical patterns. Setting the early warning thresholds based on the statistical patterns of errors enables dynamic and multi-level warnings for bridge structures.

Enhancing cold energy harvest with daytime passive radiative cooling and phase change materials integration: A numerical exploration

Daytime passive radiative cooling (DPRC) is an emerging technology to dissipate heat to the ultimate cold sink, the universe, with zero energy input. However, the achieved cold surface temperature of an object by DPRC can readily increase close to the ambient temperature. Sensible heat readily induces changes in the temperature of objects, but it generates a heat leakage path to surroundings with the largely varying temperature gradients. To address the challenge, we designed a DPRC coating integrated with phase change materials (PCM) so as to harvest and store the cold energy, respectively from the universe. To evaluate the feasibility of this concept, a numerical model, which integrates a self-programmed MATLAB code to calculate the net cooling power and a FLUENT-assisted enthalpy-porosity method to simulate the phase change process, was developed and validated. Also, the cold energy harvesting performance of the proposed device was explored under different climate types and conditions. We found that the surface temperature of the PCM with a DPRC coating can be reduced to −15.9 °C and −4.5 °C in a day in the temperate continental climate and the subtropical desert climate, respectively, when the non-radiative heat transfer is completely avoided. The temperature difference in the PCM is less than 1.0 °C when aluminum fins are added to enhance the heat transfer performance of the PCM. This study provides new insights into the continuous steady cooling of DPRC using PCMs, and the harvested cold energy can be used to cool water for the condenser of an air conditioner to save energy consumption.

Temperature-driven coupled transport of pollutants and suspended particles established by granular thermodynamics

The temperature-driven effects on pollutant transport are significant, including thermal diffusion of pollutants, thermal osmosis of solutions, thermal motion of suspended particles, and other deformation and transformation processes. The pollutant seepage field equation was derived based on granular thermodynamics, and the motion equation of suspended particles was derived from Newton's second law. A comprehensive coupled transport model for the two-phase flow of pollutants and suspended particles in saturated porous media was established, which can effectively consider the impact of temperature driving. The model accurately described the coupled transport process of pollutants and suspended particles under different temperatures and particle sizes during single-pulse injection. Furthermore, the application of this model in natural clay layers under varying temperature gradients was discussed. The results indicated that, for the same time, an increase in temperature at the high-temperature end led to a 36.5 % decrease in the peak concentration of pollutant transport. When the temperature difference was significant, thermal osmosis and thermal motion were the main mechanisms for the coupled transport of pollutants and suspended particles, with the diffusion mechanism induced by concentration and temperature gradients not dominating. Thermal diffusion positively drove the transport of pollutants, while thermal osmosis and thermal motion under temperature gradients had a reverse inhibitory effect on pollutant transport.

Optical Signal Investigation of Monolayer MoS2 Grown Via Glass-Assisted CVD On Patterned Surfaces

Enhancing photoluminescence (PL) in single-layer transition metal dichalcogenides has garnered significant interest, particularly for advancing high-performance 2D electronics and optoelectronics. The combination of surface engineering and contemporary growth methods has provided a platform for investigating optical signals. In this study, we present variations in PL and Raman signals of single-layer MoS2 flakes grown conformally using the glass-assisted CVD method on square-patterned surfaces with varying well depths. PL spectroscopy revealed a systematic and pronounced enhancement in intensities as the valley thickness decreased from 285 nm to 225 nm. Conversely, for the hill regions of the samples, the PL intensity initially increased with decreasing valley thickness and then decreased, despite the hill regions having a constant thickness of 300 nm. On the other hand, PL maps did not exhibit a systematic dependence of intensities on the hill-valley thickness distinction, contrary to expected results based on literature data for similar materials on flat surfaces. The origin of the intensity oscillations was attributed to possible mechanisms, including thickness-dependent interference and strain-related exciton funneling effects. Additionally, Raman measurements revealed irregular variations in intensity in hill regions, dependent on the thicknesses of the underlying SiO2 layers. Furthermore, we observed that the sizes of the flakes increased as the well depths of the underlying patterned surface decreased. This phenomenon might be attributed to alterations in the carrier gas flow pattern and varying temperature gradients between the hills and valleys. These results hold substantial potential to open new avenues for the integration of 2D transition metal dichalcogenides into on-chip electronic and optoelectronic devices.

Numerical simulation study on growth rate and gas reaction path of InN-MOCVD with Close-Coupled showerhead reactor

Numerical study on the influence of the carrier gas (H2 and N2), V/III ratio, inlet temperature, and pressure on gas reaction path and growth rate of indium nitride (InN) thin film in metal–organic chemical vapor deposition (MOCVD) with close-coupled showerhead (CCS) reactor was conducted. It was found that the concentrations of precursor for InN film and nanoparticle determine the growth rate and gas reaction path. InN exhibits greater difficulty in undergoing pyrolysis reactions compared to AlN and GaN. Under the conditions of this study, the gas reaction path of InN-MOCVD be dominated by adduct/amide formation path. When H2 is used as the carrier gas, the effect of H radicals on gas reactions is relatively minor, while the effect of NH2 radicals generates more nanoparticles, and significant changes in flow fields are observed compared to using N2 as the carrier gas. Under the conditions of low V/III ratio, low inlet temperature, high pressure, and low gas flow rate, the growth rate is relatively high, but the growth uniformity is decreased. There are different reasons for the effects of the above parameters, such as, altering TMIn flow to change V/III ratio and precursor concentration, varying temperature gradient due to changes in inlet temperature, and increased the particle collision frequency and residence time due to high pressure and low gas flow rate.

Digital twins to quantify the impact of growing variability on the harvest quality of orange

The quality of citrus fruit is influenced by various growing conditions, including weather. However, the impact of weather differences between growing regions on citrus quality at harvest is not well understood. This study employs a mechanistic-driven digital replica of the growth process of a Valencia orange from fruit set until harvest to quantify this impact. Measured daily temperature, humidity, rainfall, solar radiation, and wind speed data from various orange growing regions of South Africa, including Citrusdal, Nelspruit, Letsitele, and Sundays River Valley (SRV), inform and drive this digital model. The results suggest that the differences in weather conditions between growing regions significantly affect fruit diameter (FD), fruit weight (FW), rind thickness (RT), rind weight (RW), total soluble solids (TSS), titratable acidity (TA), and °Brix/acid ratio of oranges at harvest. The differences between growing regions led to variations of up to threefold for FD, twofold for FW, RT, RW, TSS, °Brix/acid ratio and up to fourfold for TA upon harvest. Particularly, oranges produced from warmer Letsitele and Nelspruit regions are found to be larger, sweeter and less acidic compared to those from coastal SRV upon harvest. The study also reveals the impact of the fruit growth process on the temperature gradient within the fruit, which varies across growing regions. The maximal temperature difference between the fruit core and surface during the growth process ranges from 4 °C to ∼7 °C. These variations in fruit temperature gradient could lead to variations in temperature-driven quality decay of fruit from different climatic regions at the start of their postharvest journey. These findings provide valuable insights for the citrus industry, aiding to optimize practices, harvest planning, and postharvest logistics. The output of this digital twin will help identify areas needing extra precooling to extend postharvest shelf life and minimize quality decay. Real-world use allows growers to schedule harvests based on regional weather conditions.

Nonsignificant elevational trends of soil microbial respiration and temperature sensitivity in a subtropical forest

AbstractSoil carbon (C) cycling plays a critical role in regulating global C budget and atmospheric CO2 concentrations. The ongoing global warming potentially accelerates soil C loss induced by microbial respiration (MR) and makes soil a large C source to the atmosphere. Quantifying the drivers of MR and its response to rising temperature (also called temperature sensitivity, Q10) should be a high priority to improve the modeling and prediction of terrestrial C cycle under global warming. In this study, we applied a standardized soil sampling along nine gradients from 410 to 1080 m in a subtropical forest in southern China. All soil samples were incubated at varying temperature gradients (10–15–20–25–20–15°C) to measure MR and Q10 every day for three weeks. Then all the measured MR was adjusted by the field temperature of each elevation gradient. Our objectives were to examine the response of MR and Q10 to the environmental change induced by elevational gradients in the subtropical forest and then quantify their main drivers. We totally collected 54 abiotic and biotic factors relative to the MR and Q10. Our results showed that the incubated MR increased from low to high elevation. However, a significant elevation trend of the adjusted MR was not examined after adjusting the field temperature of sampling sites, due to the trade‐off between increasing soil C concentration and declining temperature as elevation increased. We further found that the elevational gradients did not cause significant change in Q10. The variation in Q10 was negatively dominated by soil C quality, which declined nonlinearly along the elevation gradients. This study highlights the trade‐off between environment and biotic factors in determining soil C decomposition along elevational gradients. The uncertainty of MR measurements caused by unifying incubated temperature should not be ignored in future model development.

Dynamical Importance of the Trade Wind Inversion in Suppressing the Southeast Pacific ITCZ

AbstractSea surface temperature (SST) gradients are a primary driver of low‐level wind convergence in the east Pacific Inter‐Tropical Convergence Zone (ITCZ) through their hydrostatic relationship to the surface pressure gradient force (PGF). However, the surface PGF may not always align with SST gradients due to variations in boundary layer temperature gradients with height, that is, the boundary layer contribution to the surface PGF. In this study, we investigate the observed northern hemisphere position of the east Pacific ITCZ using a slab boundary layer model (SBLM) driven by different approximations of the boundary layer virtual temperature field. SBLM simulations using the entire boundary layer virtual temperature profile produce a realistic northern hemisphere ITCZ. However, SST‐only simulations produce excessive equatorial divergence and southern hemisphere convergence, resulting in a latitudinally confined double ITCZ‐like structure. Observed virtual temperature gradients highlight the importance of northward temperature gradients strengthening with height from the equator to 15°S below the trade wind inversion (TWI). Our interpretation is that the equatorial cold tongue induces relatively weak high surface pressure and double ITCZ‐like convergence because the resulting layer of cold air is shallow. Concurrently, relatively strong high surface pressure spreads out in the southern hemisphere due to interactions between stratocumulus clouds and the ocean surface. Together, the equatorial cold tongue and the TWI/stratocumulus clouds enable a more northern hemisphere dominant ITCZ. Thus, we provide evidence of a dynamical link between the equatorial cold tongue, low clouds, and double ITCZs, which continue to be problematic in Earth system models.

Magnetic nanofluid [formula omitted] in passive cooling system based on thermo-osmotic effect

Due to the dependence of the magnetic susceptibility of nanofluid on temperature, magnetic nanofluid is able to move in a nonuniform temperature field and an external magnetic field. In a passive cooling system based on the thermomagnetic effect, the coolant can move without the use of a pump. Here we demonstrate the principle of operation of a brand-new passive cooling system, where the convective flow of a magnetic nanofluid is driven by the combined action of thermo-osmosis and magnetic force. Therein lies the fundamental difference between the passive cooling system proposed here and the previously known systems, where the movement of ferrofluid is due to the action of the thermomagnetic effect. Based on nonequilibrium thermodynamics, a phenomenological model is proposed to describe the motion of a magnetic nanofluid in a channel in nonuniform temperature and magnetic fields. In the experimental study, the motion of ferrofluid Fe3O4 in the micro-channel is analyzed with variations in temperature, temperature gradient, channel thickness, and nanoparticle concentration. It is shown that in a non-uniform temperature field water-based ferrofluid moves in the direction of increasing temperature, while tridecane-based ferrofluid moves in the direction of decreasing it. If the thickness of the micro-channel exceeds a certain critical value, then the movement of ferrofluid under the influence of thermo-osmosis degenerates. It has been established that with an increase in concentration of nanoparticles the velocity of ferrofluid motion decreases due to the opposite direction of nanoparticle motion under the action of thermophoresis and the motion of liquid under the action of thermo-osmosis.

Investigating the Impact of Substrate Preheating on the Thermal Flow and Microstructure of Laser Cladding of Nickel-Based Superalloy.

The preheating of the substrate in laser additive superalloys can reduce residual stress and minimize cracking. However, this preheating process can lead to changes in the heat transfer conditions, ultimately affecting the resulting microstructure and mechanical properties. In order to explore the influence of substrate preheating on the formation of laser cladding, this research focuses on investigating the characteristics of Inconel 718, a nickel-based superalloy, as the subject of study. To simulate the temperature and flow field of laser cladding, a 3D computational fluid dynamics (CFD) model is employed. By varying the initial preheating conditions, an investigation is conducted into the distribution of the temperature field under different parameters. This leads to the acquisition of varying temperature gradients, G, and solidification speeds, R. Subsequently, an analysis is carried out on both the flow field and solidification microstructure in the melt pool. The results demonstrate that the preheating of the substrate results in a slower cooling rate, ultimately leading to the formation of a coarser microstructure.

Electric Field Regulation of DC-GIS Spacer by Surface Conductivity Gradient Coatings under Variable Temperature Gradients

Electric Field Regulation of DC-GIS Spacer by Surface Conductivity Gradient Coatings under Variable Temperature Gradients

Asymptotic Stability of Equilibrium States with Variable Temperature Gradient to the Boussinesq System Without Thermal Conduction

Asymptotic Stability of Equilibrium States with Variable Temperature Gradient to the Boussinesq System Without Thermal Conduction

Temperature compensation in high accuracy accelerometers using multi-sensor and machine learning methods

Temperature is a major source of inaccuracy in high-sensitivity accelerometers and gravimeters. Active thermal control systems require power and may not be ideal in some contexts such as airborne or spaceborne applications.We propose a solution that relies on multiple thermometers placed within the accelerometer to measure temperature and thermal gradient variations. Machine Learning algorithms are used to relate the temperatures to their effect on the accelerometer readings. However, obtaining labeled data for training these algorithms can be difficult. Therefore, we also developed a training platform capable of replicating temperature variations in a laboratory setting.Our experiments revealed that thermal gradients had a significant effect on accelerometer readings, emphasizing the importance of multiple thermometers.The proposed method was experimentally tested and revealed a great potential to be extended to other sources of inaccuracy as well as to other types of measuring systems, such as magnetometers or gyroscopes.

Design and analysis of thermoelectric energy harvester with 85.6% peak end-to-end efficiency and 38 mV self-startup using 4.13 mΩ/°C indirect temperature dependent MPPT

We present an efficient power management system (PMS) to harvest energy from thermoelectric energy generators (TEGs) via indirect temperature tracking. The PMS includes a power converter with an indirect temperature-dependent (ITD) maximum power point tracking (MPPT) controller and two complementary self-startups. The ITD-MPPT controller consists of an ITD input sampling circuit (ITD-ISC) and an ITD impedance matching circuit (ITD-IMC). The ITD-ISC detects and samples the TEG voltage (VTEG) under dynamically varying temperature gradients. The ITD-ISC removes unnecessary detachments of the converter from multi-mode reconfigurable TEGs to recover the otherwise wasted power using an adaptive input sampling (AIS) technique. The ITD-IMC adjusts the on-time of the power switch to control the input impedance (RIN) of the converter with a relatively high resolution of 4.13 mΩ/°C. This approach provides an ultrawide range source tracking from 2 Ω to 200 Ω. We also present a precision zero current switching (ZCS) controller to manage the on-time of the two power switches simultaneously. Two complementary self-startup components are realized using transformer-based (TSC) and charge-pump-based startup circuits (CSC). Integrated circuits for the PMS are fabricated using 180 nm and 28 nm CMOS processes for high efficiency and low voltage, respectively. The measurements indicate that the proposed PMS achieves an end-to-end efficiency (ηEE) above 80% over a wide source VTEG range (100 mV – 450 mV). The peak ηEE of 85.6% is achieved for VTEG = 200 mV, demonstrating the high-performance MPPT using indirect temperature tracking. TSC and CSC demonstrate successful self-startups at input voltages of 38 mV and 200 mV, respectively, thus providing reliable startup methods for various renewable energy sources.

Data-driven model based adaptive feedback-feed forward control schemes for open cycle - OTEC process

Open Cycle - Ocean Thermal Energy Conversion (OC-OTEC) is one of the most important renewable energy sources that generate electricity and fresh water from seawater utilizing the temperature gradient between the warm surface seawater and the cold deep seawater. This paper aims to develop non-linear data-driven model-based adaptive Feedback Control (FBC) schemes for the OC-OTEC process to track the output power and a dynamic Feed-Forward Control (FFC) scheme to reject the effects of temperature disturbance on power caused by climate variations in OC-OTEC. The experiments are conducted on a laboratory-scale OC-OTEC experimental setup at the National Institute of Ocean Technology, Chennai. Firstly, linear data-driven models are developed using system identification techniques. Based on the developed models, gain scheduling-based adaptive control schemes are developed: Proportional Integral (PI) control and Model Predictive Control (MPC). Secondly, the closed-loop performances of the developed FBC schemes are analysed under servo and regulatory operations. Furthermore, it is observed from the sensitivity analysis results that the temperature disturbance highly influences output over the manipulated variable. Hence, a dynamic FFC scheme is implemented to reject known disturbance of 1 °C variation in temperature gradient from 18 °C to 19 °C due to Sea Surface Temperature (SST) changes in temperature gradient. The results show that the proposed MPC-based FBC-FF scheme effectively enhances the tracking and disturbance rejection performance compared to the PI-based FBC-FF control scheme with a minimum Integral Square Error (ISE) of 3.055 and Control Effort (CE) of 7.505. This experimental data-based, data-driven modelling and adaptive control research provides a new direction for automating OC-OTEC. Further, these studies will help to develop a rugged and automated upscaling OC-OTEC plant control system with proposed feasible control schemes.

Technique and results of determination of vertical variations in rock thermal properties, temperature gradient and heat flow

The paper describes the results of experimental geothermal studies of the formation surrounding Savitskaya-300 well (depth 3555 m) drilled in the Volga-Ural oil and gas basin (Orenburg region, Russia). The work was aimed, firstly, at obtaining geothermal data for basin modeling and, secondly, at improving the instrumental and methodological foundations of experimental studies. Continuous core profiling of the rock thermal conductivity, volumetric heat capacity, and thermal anisotropy was performed on all 2886 recovered core samples with the total length of 329.1 m. Additional measurements were conducted at fluid saturation and elevated temperatures. For non-cored intervals, the rock thermal properties were determined from well-logging data and via measurements on rock cuttings. The studied formation is characterized by high thermal heterogeneity at both the level of strata (horizons) and individual samples. Significant thermal anisotropy up to 1.50–1.66 in the lower part of the well has been observed. To obtain data on vertical variations of equilibrium temperature and its gradient, temperature logging was performed 7 times within the 2 to 186 days of well shut-in. New data on the recovery of temperature and its gradient after drilling are important for the practice of applied and fundamental geothermal surveys. A significant increase in heat flow with depth was established based on the results of temperature gradient and rock thermal conductivity determination for 34 depth intervals. The observed general vertical variation in the whole depth range of the well up to ∼3.3 km depth can be attributed to paleoclimatic effect in the Late Pleistocene-Holocene, while the sharp increase in heat flow at ∼3.3 km within Fransian sediments is possibly due to advective heat transfer by fluid filtration. The apparent heat flow was established to be 84.3 mW⋅m−2 in the lower section of the well, below 3.3 km. The value may be close to the steady-state heat flow value, which is 84% higher than the previous published average data for the studied area.

Orbitally-forced meridional shifts of the westerlies modulated the hydroclimate of northeast China during the late Eocene

The mid-latitude westerlies are a fundamental component of the global climate system. There has been extensive research about how meridional shifts of the westerlies influenced the wet-dry paleoclimate regimes of mid-latitude Asia during the Quaternary. However, how the westerlies operated in much older geological times, such as the late Eocene, particularly on an orbital time scale, is not fully understood. Here, we conducted detailed cyclostratigraphic and palynological analyses on a late Eocene (41.2–37.8 Ma) mudstone-shale sedimentary sequence from the Fushun Basin in northeast China, which uniquely records orbitally-forced meridional shifts of the westerlies. Cyclostratigraphic analyses reveal that the mudstone-shale rhythms exhibit a prominent short eccentricity cycle, with a modest expression of obliquity cycles and a weak expression of precession cycles. The palynological results show that the vegetation experienced frequent alternations between semi-desert and swamp forest, and the climate exhibited periodic oscillations between warm-dry and cold-wet climates. We propose that a combination of eccentricity-modulated low-latitude summer insolation and obliquity-forced high-latitude incipient ice sheet and meridional temperature gradient variations drove cyclical vegetation and hydroclimate fluctuations in northeast China during the late Eocene by regulating the intensity and displacement of the westerlies and the subtropical high. Our results imply that continued poleward movement of the westerlies and the subtropical high will lead to increased aridification along the southern margin of the westerlies under a continuous global warming scenario.