Abstract The formation of midlatitude heatwaves (HWs) is closely linked to quasi‐stationary anticyclonic flow anomalies, which are often associated with so‐called omega blocking. However, not all HWs require atmospheric blocking, especially over Southern and Central Europe, where they can also be enabled by poleward extensions of the subtropical high‐pressure belt. We propose that HWs forming under omega blocking may differ in Lagrangian characteristics from those related to subtropical ridges, in terms of both air‐mass origin and processes warming air parcels en route to Central Europe. With this aim, we select the 25 most archetypical cases of omega‐ and ridge‐type Central European HWs, respectively, during the period 1950–2023. Using ERA5‐based backward trajectories and a Lagrangian temperature decomposition, we assess both air‐mass origin and the relative importance of the heat‐generating processes: advection, adiabatic warming through subsidence, and diabatic heating. Our analysis shows that adiabatic warming and diabatic heating are the dominant near‐surface heat‐generating processes for both circulation types. Advection does not contribute to omega‐type HWs, while ridge‐type HWs show small but significant contributions by advection, as air masses originate from more southern, climatologically warmer regions. Adiabatic warming is more significant in ridge‐type HWs, while omega‐type HWs see a significantly stronger role of diabatic heating due to a combination of less diabatic cooling in the free troposphere and longer air‐mass residence in the boundary layer. At higher levels (800 hPa), high temperatures are only attributable to advection and adiabatic warming. Significant differences between both circulation types emerge only two days after HW onset, when advection becomes dominant and significantly more important in ridge‐type HWs than in omega‐type HWs. These results highlight the importance of the atmospheric circulation and thus the associated air masses to the development of HWs, with implications for both weather forecasting and climate‐change perspectives.

Abstract Biases in tropical cyclone model forecasts impact track, intensity, and structural predictions. Yet, not all of these biases can be assessed using traditional comparisons with observations. This paper fills this research gap by introducing a new model evaluation framework that compares single forecasts to aircraft data from individual flights. Measurements from the novel compact Raman lidar are supplemented by dropsonde and tail Doppler radar data to explore how low-level tropical cyclone kinematics and thermodynamics evolve, particularly in the atmospheric boundary layer. The compact Raman lidar is essential in this framework, as it provides extensive thermodynamic data coverage in the tropical cyclone eye and rainbands. As a demonstration, observations are compared to short lead time COAMPS-TC forecasts of Hurricane Sam (2021) over three sampling periods to diagnose model biases. Two important low-level biases consistently appear: the modeled rainband atmospheric boundary layer has a positive moisture bias, and the modeled low-level eye has a cold bias. Despite these consistent thermodynamic differences, Sam’s primary and secondary circulations vary between flights, suggesting that mean tropical cyclone kinematics alone do not drive these temperature and moisture biases. This unique analysis framework focuses on individual flight legs, hinges on the high spatial density of the compact Raman lidar thermodynamic data, and provides an avenue for future model improvement via atmospheric boundary layer scheme adjustments.

Abstract. There were PM2.5 heavy pollution events in the Bohai Rim regions in China over the past decade, which can significantly affect radiative forcing (RF). However, the characteristics and influencing factors of RF on heavy pollution days, and its relative importance to precipitation remain unclear. This work combined ground-based and satellite observations and reanalysis data to investigate the RF characteristics of regional PM2.5 heavy pollution in the Bohai Rim regions during the fall and winter of 2014–2023. Additionally, the impact of meteorological vertical profiles on surface PM2.5 and pollution RF, and the importance of various factors to pollution RF and precipitation, were explored based on machine learning algorithms. The results showed that the RF on PM2.5 regional heavy pollution days can be up to approximately −70 Wm−2 at the surface, ±8 Wm−2 at top of atmosphere (TOA), and +80 Wm−2 in the atmosphere in clear-sky, with lower absolute values in all-sky. Low- to medium-altitude inversions of temperature (T) profiles in the boundary layer favored higher surface PM2.5 concentration, whereas isothermal stratification and medium- to high-altitude inversions corresponded to higher surface RF. Lower horizontal speeds and upward motion at low levels can induce higher surface PM2.5 and surface RF. Surface PM2.5 was the most important factor to surface and atmosphere RF in clear-sky, but V wind in high level (500 hPa) in all-sky. Moreover, pollution RFs in all-sky were as important as vertical winds to the total precipitation. Notably, there was considerable regional heterogeneity in the important factors affecting the RF and precipitation in the Bohai Rim regions.

Abstract. We present a protocol for scenario simulations of marine cloud brightening (MCB) solar radiation modification (SRM), which we design for inclusion as a bridge simulation in the Geoengineering Model Intercomparison Project (GeoMIP). This protocol, named G6-1.5K-MCB, parallels the existing G6-1.5K-SAI, but it simulates injecting sea salt aerosol (iSSA) into the lower marine boundary layer to create a MCB scenario. Using information taken from recent modeling studies, we propose to apply MCB iSSA emissions in the midlatitudes, which can produce a surface temperature response that more closely resembles the opposite of the greenhouse gas (GHG) warming pattern without invoking the La Niña response that has been predicted in previous studies. In many ways, this approach is analogous to the choice of emissions at 30° N and 30° S for stratospheric aerosol injection (SAI) in G6-1.5K-SAI. Owing to substantial uncertainty in the aerosol-cloud forcing from MCB, we outline recommended benchmark simulations to facilitate similar simulations of cloud brightening across different models. We present simulations of the G6-1.5K-MCB protocol using three Earth System Models (ESMs). All three ESMs show that for an intermediate baseline GHG emission trajectory, midlatitude MCB can maintain 21st century global mean surface temperature (GMST) at 2020–2039 temperatures. The iSSA emission rates required to maintain this target vary by a factor of 20 across the ESMs due to differences in the size distribution of the emitted iSSA and in the representations of aerosol-cloud interactions, demonstrating the importance of benchmark simulations for both understanding uncertainties and setting up the scenario simulations. Temperature and precipitation anomalies are greatly reduced relative to the GHG warming background, with most regions experiencing no statistically significant changes relative to the reference period. In some regions, there is a notable seasonal cycle in the residual climate change, though the anomalies are still much smaller than the GHG warming impact. On the basis of the promising results from this three-model testbed, we propose that the G6-1.5K-MCB serve as a basis for future model intercomparison protocols. This will enable further estimation of the structural uncertainties of ESMs in the climate response to MCB and provide a valuable dataset for more detailed analysis of the potential impacts of MCB.

Street canyons, as a key component of the urban built environment, strongly influence the diffusion and retention of particulate pollutants due to their complex airflow structures. To investigate the diffusion mechanisms of particulate matter released from different locations within street canyons, a two-dimensional idealized canyon model without vegetation was employed. A steady-state flow field was simulated using computational fluid dynamics (CFD), and a Lagrangian particle-tracking approach was applied to analyze particle trajectories and transport behaviors at different spatial positions. Results indicate the formation of a stable primary vortex within the canyon. The central region, characterized by low wind speeds and recirculating streamlines, significantly inhibits particle dispersion, whereas the upper canyon and free-flow regions promote rapid particle removal due to higher wind velocities. Particle release location plays a critical role in diffusion efficiency: particles released near the upper region or close to the free-flow boundary disperse rapidly when their initial momentum aligns with the main flow direction; particles in the vortex core are prone to long-term trapping; and particles near the ground can gradually rise due to boundary layer disturbances but exhibit prolonged residence times. Additionally, the alignment between particle initial velocity and local flow structure significantly affects their ability to escape vortex constraints. These findings highlight the sensitivity of particulate dispersion to spatial location and flow structures within street canyons, providing a theoretical basis for optimizing urban ventilation and pollution control strategies.

Abstract Observational and numerical studies of intense tropical cyclones (TCs) have occasionally noted the existence of small-scale vortical eddies along the inner edge of the eyewall in the lower and middle troposphere, which appear in plan view radar reflectivity as closely spaced filamentary, cellular, lobed, or scalloped echoes protruding inward from the primary eyewall convective ring. Using high-resolution NEXRAD data, this study examines qualitative characteristics of these wave-like coherent structures in case studies of three Atlantic hurricanes. Signatures of these coherent structures in radar base moment data, including their wave-like echo pattern, Doppler velocity perturbations, and elevated spectrum widths, are generally most pronounced at lower radar elevations and diminish with altitude. The wave-like echoes are associated with alternating positive-negative values of azimuthal Doppler velocity shear, with individual small-scale reflectivity structures approximately collocated with enhanced positive (cyclonic) azimuthal shear. These patterns, albeit sensitive to sampling factors, formed the basis from which similar wave-like structures were identified in eleven additional North Atlantic and Pacific TCs. These coherent structures were found predominantly to the left (for Northern Hemispheric storms) of the environmental vertical wind shear vector, forward and left of storm motion, and in offshore flow, implying a role of asymmetric boundary layer dynamics in their development. Our results indicate that these coherent structures are not unique to high-end TCs, and the wide range of storm structure and environments over which these structures appeared suggests that they are an intrinsic element of TC inner-core dynamics and may constitute a distinct class of TC features.

This investigation examines the momentum, thermal, and species transport characteristics of an ethylene glycol-based copper nanofluid over a rotating disk configuration, incorporating the combined influences of an aligned magnetic field and Arrhenius activation energy. The mathematical model, comprising nonlinear partial differential equations for momentum conservation, energy balance, and concentration distribution, is reduced to a system of ordinary differential equations through appropriate similarity transformations. Numerical solutions are obtained using the BVP5C algorithm, yielding detailed velocity, temperature, and concentration profiles across the boundary layer. The principal novelty of this work lies in the simultaneous consideration of activation energy effects and aligned magnetic field orientation on nanofluid behavior in rotating disk geometry, a combination not previously addressed in the literature. A systematic parametric study examines how key physical quantities like magnetic field intensity, nanoparticle volumetric concentration, activation energy parameter, and Schmidt number—influence the heat and mass transfer characteristics of the system. The results demonstrate that increasing magnetic field strength produces a retarding effect on fluid motion, with both radial and tangential velocity components diminishing as the Lorentz force intensifies. Furthermore, the activation energy parameter exhibits a pronounced influence on species transport, significantly modifying concentration distributions and mass transfer rates at the disk surface. These findings contribute to the fundamental understanding of nanofluid behavior under coupled magnetic and chemical reaction effects, with potential implications for thermal management systems and biomedical applications

Silicon-doped diamond-like carbon (Si-DLC) coatings against aluminum alloy (A5052) were investigated for reducing friction under humid conditions. The coatings were deposited on high-speed steel (SKH51) substrates using a bipolar-type plasma-based ion implantation and deposition (PBII&D) technique, with Si content controlled by varying the tetramethylsilane (TMS)-to-toluene precursor ratio. Structural characterization by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the progressive evolution of Si–C bonding with increasing TMS ratio. The Si-DLC coating with Si 5.0 at.% exhibited the lowest coefficient of friction (COF) of 0.033 and reduced wear volume under a high normal load of 150 N in humid conditions (relative humidity > 90%). However, Si-DLC coatings with higher Si contents (Si 7.7 and 14.3 at.%) led to deteriorated tribological performance, including coating delamination and severe wear. Surface analyses of the coatings revealed that the low-friction behavior was associated with the presence of oxidized Si species at the outermost surface, which undergo hydroxylation in humid environments to form Si–OH groups. These hydroxylated surfaces promote the formation of a hydrated boundary layer that provides a low-shear sliding interface.

An experimental study is conducted of the fluid-thermal-structural interaction of a clamped compliant panel exposed to the intense shock-wave/boundary-layer interaction (SWBLI) induced by a compression ramp at Mach 10. Initial measurements of the underlying flowfield with a rigid ramp showed the incoming boundary layer to be transitional, and the SWBLI was observed to vary from attached to fully separated as the ramp angle was increased from 10 to 30 . For the compliant panel, a sealed cavity behind the panel allowed the effects of pressure-differential induced strains to be studied in the context of characterizing surface response to the aero-thermal load. Full-field, time-resolved panel deformations were measured using high-speed photogrammetry enabled by a new high-fidelity marker-tracking routine, which was shown to outperform existing methods. Substantial static panel deformations (of the order of several times the panel thickness) were produced by the intense aero-thermal loading environment. These deformations, combined with induced thermal and pressure gradients across the panel, were found to significantly modify the nature of existing panel modes (both the frequency and the displacement distributions) and introduce new, irregular mode shapes not predicted by classical clamped-plate theory; SolidWorks® simulations were performed to demonstrate that these new mode shapes were a result of the underlying panel curvature. Increasing the ramp angle resulted in a wider variety of panel modes becoming excited, while increasing the pressure differential across the panel typically produced further increases in modal frequencies and decreases in vibrational amplitudes. The transient panel response was characterized and it was found that the lower frequency mode shapes tended to gradually increase in vibrational frequency as the panel heated up and further deformed; however, higher frequency modes ( ) generally showed the opposite behavior. Furthermore, as the panel deformed through the test time, the average vibrational spectra root-mean-square power was generally found to monotonically decrease.

The advancement in research, production, and use of nanofluids presents an opportunity for improving natural convective heat transfer in cavities. This study involves the numerical investigation of the natural convection in a two-dimensional hexagonal cavity fitted with a square obstacle and filled with a ternary hybrid MgO-ZnO-SiC/ethylene glycol nanofluid under steady state conditions. The research considered the effects of Rayleigh number, inclination angle, and aspect ratio on heat transfer and fluid flow in a bid to enhance thermal efficiency in the complex geometry. The governing Navier-Stokes equations were solved using the Finite Element Method in COMSOL Multiphysics. The model was first validated against benchmark results for natural convection in a differentially heated square cavity for reliability and accuracy. Additionally, the grid independence validation agrees with results literature which is an affirmation of the correctness of the numerical model. The results showed a strong transition from conduction to convection heat transfer as the Rayleigh number increased. Higher Rayleigh numbers produced stronger buoyancy-driven circulation, thinner thermal boundary layers, and appreciably high Nusselt numbers. . The average k, C_p, μ, ρ, α, and β were 0.2757449 W/m•K, 2146.9702 J/kg•K, 0.0169729 Pa•s, 137.60446 kg/m³, 1.41×〖10〗^(-05) m²/s, and 1.02×〖10〗^(-07) K-1, respectively. At Ra=〖10〗^4 and θ =0°,30°,45°,60°,and 90°, Nu values were 4.20, 4.12, 4.15, 4.22, and 4.25, respectively. At Ra=〖10〗^5 and θ =0°,30°,45°,60°,and 90°, Nu values were 5.48, 5.40, 5.42, 5.50, and 5.55, respectively. For Ra=〖10〗^2 and AR values of 0.25, 0.3, 0.35, and 0.40, Nu values were 3.50, 3.58, 3.65, and 3.75, respectively. At Ra=〖10〗^3, and AR values of 0.25, 0.3, 0.35, and 0.40, Nu values were 3.55, 3.62, 3.70, and 3.82, respectively. At Ra=〖10〗^4, and AR values of 0.25, 0.3, 0.35, and 0.40, Nu values were 4.05, 4.20, 4.40, and 4.65, respectively. At Ra=〖10〗^5, and AR values of 0.25, 0.3, 0.35, and 0.40, Nu values were 4.70, 5.10, 5.55, and 6.00, respectively. The results provide important new information for the design and optimization of passive cooling applications and natural convection-based thermal management systems using ternary hybrid nanofluids.

Severe PM2.5 pollution in basin-type cities arises from the combined effects of intensive emissions, complex terrain, and adverse meteorology. However, the accumulation mechanisms and associated health impacts in basin-type cities are still not fully characterized at high spatial resolution. This study integrates the WRF-CMAQ modeling system with the World Health Organization (WHO)-recommended Air Quality Plus (AirQ+) tool to investigate PM2.5 accumulation and related health risks in Linfen, a coal-based basin city in northern China. High-resolution simulations for January and July 2020, validated against ground observations, are used to explore the roles of valley-controlled winds, planetary boundary layer dynamics, and dry-wet deposition processes. The results show that wintertime PM2.5 levels are two to four times higher than those observed in summer, driven by shallow boundary layers (200-400m), frequent temperature inversions, and weak winds that trap pollutants along the central valley corridor, leading to persistent high-concentration zones. Diurnal analyses at valley, hilly, and mountainous sites reveal terrain-dependent accumulation patterns, with pronounced morning peaks under winter inversions in valley areas and weaker, circulation-driven variability in mountainous regions. Deposition diagnostics indicate that dry deposition dominates in winter, while strong convective mixing and precipitation enhance wet deposition in summer, promoting more efficient removal. Population-weighted exposure fields coupled with AirQ+ show that winter-related fractions for all-cause and cardiovascular mortality substantially exceed national averages, with the most-exposed 20% of residents bearing a disproportionately high health burden. This study clarifies how emissions, complex terrain, and boundary-layer processes jointly control PM2.5 accumulation in basin environments. It also provides an integrated framework for evaluating health risks and supporting equity-oriented air-quality management.

Abstract. We present a comprehensive balloon-borne measurement dataset collected during a dedicated Arctic observation campaign conducted from 19 March to 18 April 2024 in the transition from polar night to polar day at the Villum Research Station (VRS) at Station Nord in Greenland. The objective of the observations was to characterise the temporal evolution of the Arctic atmospheric boundary layer (ABL), focusing on key transition periods, including cloud development, low-level jet evolution, and day to night shifts. Data were collected by the Balloon-bornE moduLar Utility for profilinG the lower Atmosphere (BELUGA) tethered-balloon system performing in-situ measurements of temperature, relative humidity, wind speed, turbulence, and thermal infrared irradiance from the surface to several hundred meters altitude, with frequent profiling in high vertical resolution. Twenty-eight research flights delivered more than 300 profiles, with up to 8 profiles per hour, complemented by daily radiosonde launches. This paper specifies the BELUGA instrumentation at VRS, data processing procedures, and the publicly available Level-2 data (BELUGA and radiosonde), provided in instrument-separated data subsets listed in a data collection (https://doi.org/10.1594/PANGAEA.986431, Dorff et al., 2026c). One possible major application of the data is to evaluate different model types (such as numerical weather prediction, single-column, large-eddy simulations) in representing processes controlling the Arctic ABL. To prepare such evaluations, we give an overview of the observations, environmental conditions during the campaign, and highlight specific events that are valuable for model comparison. We introduce an event in which temporal temperature changes influence the ABL inversion, radiative heating-rate profiles associated with transitions between cloudy and cloud-free conditions, and an observed Arctic low-level jet compared with reanalysis, offering insights into the Arctic ABL evolution.

Abstract This paper presents an experimental investigation of the properties of long electrical arcs immersed in a crossflow. The insights gained from these experiments can be applied in numerous fields: one of which is lightning protection of aircraft. Upon initial attachment to the airplane, the lightning arc column can sweep along the plane's surface due to the relative motion between the two in a process known as the swept-stroke. The first set of experiments corresponds to meter-scale low-current D.C. arcs (3 A) attaching to an aeronautic airfoil in low speed flow (1-4 m/s), extending prior work that considered an anodic airfoil to the negative polarity case. The dynamic and electrical properties of the arc channel, as well as the dynamic motion of the cathodic arc root, are investigated through high-speed imaging, particle image velocimetry (PIV), and electrical measurements. The influences of wind speed, airfoil angle of attack (AoA), and counter-electrode configuration are explored. The second set of results applies the same data processing to high-speed videos from a previous experimental campaign conducted at ONERA on meter-long high-current D.C. arcs (200-600 A) subject to high-speed flow (40-60 m/s). Unlike the anodic arc root, the cathodic arc root is observed to either stall or sweep along the airfoil surface. In general, the root trails the leading edge of the arc column, which is advected by the flow, with the degree of lag depending on the experimental conditions. These findings enable analysis of how flow separation, boundary layer dynamics, arc regimes, and cathode emission processes influence the physical behavior of the arc column and root over two orders of magnitude in current and one order of magnitude in wind speed, providing insight into the coupled phenomena governing the swept-stroke.

The variance and spectra of wall-normal velocities are investigated for direct numerical simulations of turbulent flow in a channel, pipe and zero-pressure-gradient boundary layer across a decade of friction Reynolds numbers. Spectra along the spanwise wavenumber have a pronounced peak well described by the turbulent dissipation rate and the local shear stress throughout the bottom half of the boundary layer. Deviations in the local stress from the surface shear velocity $U_\tau$ account for almost all of the differences in wall-normal velocity variance observed across different canonical flows, including for plane Couette flow. The dependence on the local stress is attributed to the fact that wall-normal motions are predominately ‘active’ per Townsend’s attached eddy hypothesis and directly contribute to the local shear stress, noting this hypothesis assumes simplified ideal conditions with constant turbulent shear stress. A semi-empirical fit applied to the Reynolds-number dependence of the variance matches the simulations across the lower half of the boundary layer and aligns with observed values in the literature. The fit extrapolates to a value between 1.45 and 1.65 times the local shear stress in the high-Reynolds-number limit, consistent with previous predictions relative to $U_\tau$ including for the vertical velocity in the near-neutral atmospheric boundary layer. However, universality in the exact proportional constant is precluded by small discrepancies in the variances corresponding to dissimilarity in the low-wavenumber contributions across different flow configurations and wall-normal positions. We speculate the dissimilarity is due to relatively weak ‘inactive’ wall-normal motions that are excluded from Townsend’s original hypothesis.

The rotational evolution of pulsars is governed by torque mechanisms whose mathematical structure encodes fundamental symmetries of the underlying physics. We demonstrate that the standard spin-down equation f˙=−sf−rf3−gf5 derives from a discrete antisymmetry requirement, namely invariance of the torque under reversal of rotation sense, which restricts the frequency dependence to odd integer powers. We show that physically motivated plasma processes systematically break this symmetry, introducing fractional frequency exponents: viscous Ekman pumping at the crust–superfluid boundary layer (f3/2), magnetohydrodynamic turbulent dissipation via Kolmogorov and Sweet–Parker cascades (f10/3, f11/3), non-linear superfluid vortex dynamics (f5/2), and saturated r-mode oscillations (f7−2β). The central result is an exact analytical resolution of the long-standing Crab pulsar braking index puzzle: the observed n=2.51±0.01, which has defied explanation for nearly four decades, emerges naturally from the superposition of magnetic dipole radiation (f˙∝f3) and boundary layer Ekman pumping (f˙∝f3/2), with analytically derived coefficients yielding a dipole-component surface field Bp=6.2×1012 G—higher than the standard PP˙ estimate of 3.8×1012 G, because that formula conflates dipole and non-dipole torques, but lower than applying the Larmor formula to the full spin-down rate (7.6×1012 G), since 32.7% of the total torque is non-radiative boundary-layer dissipation. We develop the Riemann–Liouville fractional calculus formalism for these equations, showing that fractional derivatives break time-translation symmetry through intrinsic memory effects, with solutions expressed in terms of Mittag-Leffler and Fox H-functions that interpolate continuously between exponential (fully symmetric) and power-law (scale-free symmetric) relaxation. Lambert–Tsallis Wq functions with non-extensive parameter q encoding broken statistical symmetry enable equation-of-state-independent inference of neutron star compactness and tidal deformability. Our framework establishes a unified symmetry-based classification of pulsar spin-down mechanisms and predicts frequency-dependent braking indices evolving at rate dn/dt∼2×10−4 yr−1, yielding Δn≈0.01 over 50 years—testable with current pulsar timing programmes. The formalism provides a coherent theoretical foundation connecting plasma microphysics at the neutron star interior to macroscopic observables in electromagnetic and gravitational wave channels.

The present work explores the intricate thermo-fluid dynamics of Newtonian and non-Newtonian nanofluids flowing over a porous, deformable stretching surface. The analysis incorporates the combined influences of thermal radiation, thermophoretic force, Brownian motion, and dual-phase-lag models of heat and mass diffusion. Darcy–Forchheimer drag and slip boundary effects are also considered to represent realistic flow resistance within porous media. Through similarity transformations, the governing nonlinear partial differential equations are reduced to ordinary differential form and numerically solved using MATLAB’s bvp4c algorithm. The study reveals that enhanced permeability and slip parameters attenuate fluid motion, whereas intensified Brownian motion and porous resistance elevate the thermal boundary layer. The findings confirm that nanofluids offer superior heat transport capabilities, making them promising candidates for applications in thermal regulation and biomedical heat exchange systems. Model validation against previously published results demonstrates strong agreement, reinforcing the reliability of the numerical approach.

Microstructures of amphibole clusters in mafic magmatic enclaves of the Early Cretaceous Sanguliu granitic pluton in East China: insights for chaotic magma mixing processes in a hybrid boundary layer

ABSTRACT The land surface‐air temperature difference ( T s − T a ) is a key parameter in land‐atmosphere energy exchange. As the core driver of sensible heat flux, it regulates turbulent motion and vertical thermal structure, directly impacting near‐surface stability, boundary layer development, and extreme climate events. This study evaluates the performance of reanalysis products in simulating T s − T a over the Contiguous United States (CONUS), using observations from more than 100 U.S. Climate Reference Network (USCRN) stations during 2002–2024. Results show that ERA5 and ERA5‐Land reproduce the spatial pattern of T s − T a reasonably well, but exhibit systematic biases: both reanalyses datasets significantly underestimate the daily maximum T s − T a (occurring during daytime), with mean biases of −3.1°C and −3.4°C averaged over CONUS, and the largest underestimation found in the arid southwestern United States during summer. Terrain analysis further reveals that these biases are topography‐dependent: models consistently underestimate nocturnal T s − T a in valleys, where cold‐air pooling occurs, while ERA5‐Land overestimates nighttime T s − T a over flat and elevated terrain in summer and autumn. Benefiting from its higher‐resolution land surface model, ERA5‐Land shows some improvement over ERA5, reducing the daily mean bias from −0.9°C to −0.6°C and the daily minimum bias from −0.8°C to +0.4°C. However, both reanalysis products fail to capture the observed significant decreasing trend in minimum T s − T a (−0.52°C ± 0.005°C/decade in observations versus +0.02°C/decade in ERA5 and +0.01°C/decade in ERA5‐Land). This discrepancy is attributed to the assumption of synchronous trends in surface temperature and air temperature within the reanalysis systems, revealing limitations of current reanalysis products in representing the long‐term dynamics of land‐atmosphere interaction. This study provides a scientific basis for optimising climate models and informing reanalysis data applications.

Spanwise wall oscillation (SWO) of turbulent boundary layers (TBLs) is investigated via direct numerical simulations (DNS) over an extended actuation region (momentum Reynolds number $344\lt Re_\theta \lt 2340$ ) with oscillation periods up to $T_{\textit{sc}}^+=600$ , scaled by the uncontrolled friction velocity $u_{\tau 0}$ at the onset of SWO (i.e. $ \textit{Re}_\theta =344$ ). For low periods ( $T_{\textit{sc}}^+\lt 200$ ), drag reduction ( $ \textit{DR} $ ) decreases with increasing $ \textit{Re}_\theta$ , consistent with conventional inner-scaled control strategies targeting near-wall turbulence. In sharp contrast, for large periods ( $T_{\textit{sc}}^+\gt 200$ ), $ \textit{DR} $ increases with $ \textit{Re}_\theta$ . For example, at $T_{\textit{sc}}^+=600$ , $ \textit{DR} $ rises from 1.3 % at $ \textit{Re}_\theta =713$ to 7.0 % at $ \textit{Re}_\theta =2340$ . This unexpected growth is partly explained by the streamwise evolution of the effective oscillation parameter: as a TBL develops, $u_{\tau 0}$ decreases downstream, reducing the local-scaled period $T^+$ and thereby enhancing suppression of near-wall turbulence. Interestingly, if the results are compared at approximately fixed $T^+$ , then $ \textit{DR} $ for $T^+\gt 350$ still exhibits a weak positive dependence on $ \textit{Re}_\theta$ , consistent with recent experiments by Marusic et al. (2021, Nat. Commun. , vol. 12, 5805). We further develop a new analytical relationship that links $ \textit{DR} $ to the upward shift of mean velocity in the wake region. Unlike previous formulations, the relationship avoids logarithmic-region fitting and does not rely on an invariant Kármán constant under SWO, while maintaining good agreement with DNS data. Flow diagnostics – including Reynolds stresses, skin-friction decomposition, and energy spectra – demonstrate that the observed variation of $ \textit{DR} $ with Reynolds number ( $ \textit{Re}$ ) arises from period-dependent modulation of near-wall turbulence. Overall, these findings challenge the conventional view that $ \textit{DR} $ inevitably deteriorates with $ \textit{Re}$ , and demonstrate that out-scaled actuation can instead enhance $ \textit{DR} $ performance – offering new physical insights for high- $ \textit{Re}$ control strategies.

Minor differences in airflow are often assumed to have negligible physiological effects, yet they directly modify heat- and gas exchange by altering the leaf boundary layer. We investigated how sustained low airflow impacts mechanisms regulating leaf-microclimate exchange, and how these responses shape acclimation in Lactuca sativa and Solanum lycopersicum. Lettuce was grown under two low-velocity airflow regimes (0.22 and 0.65 m s-1), and changes in the leaf surface microclimate, plant transpiration, stomatal regulation, leaf photosynthesis, and growth were quantified. Increased airflow elevated transpirational demand, to which stomata responded dynamically by closing, increasing intrinsic water-use efficiency. This closure did not fully offset enhanced water loss and was constrained by the need to maintain CO2 assimilation, which revealed that airflow alters a functional trade-off between carbon gain and water loss. This trade-off varied spatially, as photosynthetic limitation emerged specifically on the adaxial leaf side, indicating humidity-driven, side-specific diffusion limitations. At the whole-plant scale, increased airflow reduced fresh weight and leaf length by ca. 13%, associated with hydraulic constraints and thermal regulation. We propose a unifying theory in which physiological regulation to airflow constrains structural and leaf-level acclimation, setting limits for plant growth. This framework provides a mechanistic understanding on how airflow affects short-term feedback and acclimation, with important consequences for experimental interpretation and reproducibility.