Search Results (556)

The thermosphere serves as a pivotal region for Sun–Earth interactions, and thermospheric winds are of great scientific importance for deepening insights into atmospheric dynamics, climate formation mechanisms, and space environment evolution. This study designed and developed a Ground-based Doppler Asymmetric Spatial Heterodyne Interferometer (GDASHI). Targeting the nightglow of the oxygen atomic red line (OI 630.0 nm), this instrument enables high-precision observation of thermospheric winds. The GDASHI was deployed at Gemini Astronomical Manor (26.7°N, 100.0°E), and has obtained one year of nighttime meridional and zonal wind data. To verify the reliability of GDASHI-derived winds, a collocated observation comparison was performed against the Dual-Channel Optical Interferometer stationed at Binchuan Station (25.6°N, 100.6°E), Yunnan. The winds of the two instruments are basically consistent in both their diurnal variation trends and amplitudes. Further Deming regression and correlation analysis were conducted for the two datasets, with the meridional and zonal winds yielding fitting slopes of 0.808 and 0.875 and correlation coefficients of 0.754 and 0.771, respectively. An uncertainty analysis of the inter-instrument comparison was also carried out, incorporating instrumental measurement uncertainties, instrumental parameter errors, and small-scale perturbations induced by observational site differences; the synthesized total uncertainties of zonal and meridional winds are determined to be 20.24 m/s and 20.77 m/s, respectively. This study not only verifies the feasibility and reliability of GDASHI for ground-based thermospheric wind detection but also provides critical observational support for analyzing the spatiotemporal variation characteristics of mid-low latitude thermospheric wind fields and exploring their underlying physical mechanisms. Full article

This study investigates the solar origins of short-term periodicities in the near-Earth solar wind and interplanetary magnetic field (IMF) using long-term observations (1995–2024) and Potential Field Source Surface modeling. We establish that the 27-day periodicity in solar wind speed and its harmonics (13.5-day and 9-day) are governed by the combined influence of polar and low-latitude coronal holes. Polar coronal holes serve as the fundamental stabilizers of the global coronal structure, while the rotation of the Sun in the presence of low-latitude coronal holes acts as the primary mechanism generating periodic fluctuations. The absence of low-latitude coronal holes diminishes or erases these periodicities. For IMF components forming the Parker spiral, the periodicity is controlled by the structure of the heliospheric current sheet (HCS). A stable 27-day period emerges under a two-sector IMF configuration (HCS average slope $\mathrm{SL}>0.4$, latitudinal extent beyond ±30°), while a stable four-sector structure ($\mathrm{SL}>0.6$, latitudinal extent beyond ±60°) superimposes a clear 13.5-day periodicity. However, periodicity weakens or disappears when the HCS is flat and equatorial, or when global structural changes and transient disturbances disrupt recurrence patterns. In contrast, $B_z^{\mathrm{GSE}}$ exhibits weak periodicity due to its transient nature, while $B_z^{\mathrm{GSM}}$ shows intermittent 27-day periodicity modulated by the Russell-McPherron effect. Consequently, geomagnetic indices (Kp, Dst, AE) display periodic behavior similar to $B_z^{\mathrm{GSM}}$, consistent with its crucial role in solar wind-magnetosphere coupling. These results quantitatively link solar surface morphology to heliospheric recurrence, clarifying the conditions under which periodicities emerge or are suppressed throughout the Sun-Earth system. Full article

With the increasing frequency of maritime activities, large-scale man overboard incidents raise higher demands on maritime search and rescue (SAR) decision-making. Most existing drift models are designed for single-person-overboard situations and have limited ability to model multiple-persons-in-water (MPIW) scenarios. To address this gap, this study proposes a drift trajectory prediction method for MPIW based on full-scale field experiments in the Xisha Sea, South China Sea. In December 2023, six drift experiments were carried out, providing 57 h of tracking data under typical conditions with wind speeds from 0.17 to 7.77 m/s and surface current speeds from 0.06 to 0.96 m/s. Two basic MPIW scenarios were considered, side-by-side connection and random connection, and four MPIW drift models were built for upright 3-person (UP_3), upright 5-person (UP_5), upright–facedown–upright (U-F-U) and facedown 2-person (FD_2). The corresponding wind-induced drift coefficients were estimated. The stochastic variability of the crosswind leeway (CWL), including sign-change frequency and the probability of positive CWL, was systematically analyzed. For unconstrained regressions, the downwind leeway slope coefficients range from −2.96% to −12.61%, while CWL slope coefficients range from 1.01% to 2.78%, depending on group configuration. Monte Carlo simulations were then used to compare different model groups. In typical test cases, the proposed MPIW models reduce the normalized cumulative error for 11 h trajectory prediction from 0.18–0.23 to 0.08–0.17, indicating a clear improvement in the accuracy of search area delineation for group drowning scenarios. The results provide a useful reference for MPIW drift prediction and SAR decision-making in similar offshore and deep-water environments. Full article

Downbursts generate strong and transient near-surface winds that significantly influence wind flows over complex terrains. In this study, two downburst models—the impinging jet model representing the near-field region and the wall jet model representing the fully developed outflow—were experimentally investigated. The study examined the characteristics of mountain wind fields within the fully developed region, considering variations in mountain height, slope, shape, and radial position. Results show that mountain height and shape exert only minor influences on the mountain speed-up ratio, whereas slope and radial position play dominant roles: the acceleration ratio decreases with increasing radial distance and with steeper slopes. The near-surface flow is mainly affected within a vertical range of approximately 1.5 times the mountain height and a radial distance of about four times the height. By explicitly comparing the two models, this study provides the quantitative experimental relationship linking the vertical position of maximum horizontal velocity between impinging jet and wall jet flows. The comparison of mountain wind fields under equivalent positions demonstrated consistent speed-up ratios, confirming that the wall jet model can effectively reproduce the fully developed stage of downburst winds over mountainous terrain. Thus, this work offers new experimental evidence and a validated modeling framework for studying mountain wind effects under downburst conditions. Full article

During the summer fire season in the Greater Khingan Mountains, weak synoptic winds allow local mountain–valley breeze systems to predominantly influence fire spread. However, their dynamic effects remain insufficiently quantified, limiting fire forecasting accuracy. This study analyzes a decade of summer meteorological data and a high-resolution WRF-Fire simulation of a 2023 wildfire to investigate wind patterns and their impact on fire behavior. Results reveal pronounced diurnal and spatial wind variability, with low directional persistence and concentrated nighttime distributions. Under low-wind conditions, mountain–valley breezes shift from upslope during the day to downslope flows at night. Simulations and observations indicate higher nighttime wind speeds on slopes and higher daytime speeds in valleys, reflecting the combined effects of thermal circulation and gravitational acceleration. The WRF-Fire model effectively reproduced the wildfire’s macro-scale spread pattern, showing strong agreement with satellite-derived burn scars in mountainous regions. Fire progression was influenced by five distinct phases, with nocturnal mountain winds and topographic channeling accelerating spread. These highlight the role of terrain-driven mountain–valley breezes in fire propagation and provide insights to improve fire forecasting and management strategies in mountainous regions. Firefighting strategies must account for the diurnal cycle of wind, particularly the contrast between strong nighttime winds at higher altitudes and stable valley conditions. Full article

A complex operating environment poses significant challenges to the design of ramjet combustion chambers as high-enthalpy wind tunnels and their associated high-temperature, high-pressure combustion chambers continue to advance. This study developed a thermal–fluid–structure coupling finite element (FE) model based on the computational fluid dynamics (CFD) numerical simulation method to simulate the service conditions of combustion chambers under varying structures. Subsequently, FE simulation results were used to study the influences of combustion chamber structure on fluid flow characteristics, variation in cooling water pressure, temperature and stress of a combustion chamber wall. The results showed that after cooling water entered the chamber as a stable jet, it impacted the wall surface and formed a bidirectional vortex flow, which then entered the cooling water channels. Modifying the slope of a cooling water channel can effectively reduce pressure within the combustion chamber. It is noteworthy that the inlet equivalent stress of a combustion chamber decreases with an increasing slope, whereas outlet equivalent stress increases correspondingly. Finally, through comprehensive analysis, the optimal slope of a cooling water channel was determined to be 0.3°. This work provides essential theoretical insights for optimizing the design of combustion chambers. Full article

Habitat fragmentation due to anthropogenic pressures threats functional connectivity across landscapes for flying mammals. Tadarida brasiliensis depends on nocturnal movement corridors linking refuge and foraging areas, yet these pathways are increasingly constrained in semi-arid regions of northern Mexico. This study developed and analyzed the potential ecological corridors connecting the main colony of T. brasiliensis located in Santa Eulalia with the Irrigation District 005 Delicias, in Chihuahua, Mexico. We integrated multi-source geospatial data within a geographic information system, including wind speed, terrain slope, normalized difference vegetation index, land surface temperature, distance to rivers, landscape aggregation, nighttime lighting, and distance to roads, power lines, and human settlements. Landscape resistance to movement was assessed using a combined framework based on the Analytic Hierarchy Process, the InVEST-Habitat Quality model, and Least Cost Path analysis, generating composite resistance. Five potential corridors were identified, with ranges of lengths and CWD:EucD ratios of 6.8–34.0 km and 20.4–51.3, respectively, reflecting variable cumulative resistance along pathways. Nighttime lighting and proximity to urban areas were major contributors to high resistance, particularly within urban and agricultural environments. The identified corridor network provides a spatial representation of potential routes and supports landscape-level conservation planning to mitigate anthropogenic pressures and maintain functional connectivity. Full article

The canyon hilly terrain of northwestern China significantly influences wind field characteristics within the grotto zone, consequently affecting the degree of wind erosion on grotto heritage. In the present study, computational fluid dynamics (CFD) numerical simulations were employed to investigate the effects of mountain length, slope, and spacing on the wind field characteristics of a typically canyon hilly terrain, with the Xumishan Grottoes as a case study. The results show a significant wind speed acceleration at canyon entrances and summits. Variations in mountain length and slope non-linearly affect wind field distribution, with wind speeds at the side and summit stabilizing when the mountain length exceeds three times the mountain height (L ≥ 3H). Based on the simulation results, an improved acceleration ratio formula incorporating mountain length, slope, and spacing was proposed, which demonstrated a discrepancy of only 9.05% compared with the field-validated CFD results for Cave 5 at Xumishan. This study elucidates the wind field formation mechanisms in canyon hilly terrain and provides a scientific basis for addressing the stone carving erosion of grotto heritage, contributing to the advancement of preventive conservation strategies for grottoes in complex terrains. Full article

The intensification of urban heat islands in high-density coastal slope areas poses significant challenges to sustainable development. From the perspective of sustainable urban design, this study investigates adaptive greening strategies to mitigate thermal stress, aiming to elucidate the key microclimate mechanisms under the combined influence of sea breezes and complex terrain to develop sustainable solutions that synergistically improve the thermal environment and energy efficiency. Combining field measurements with ENVI-met numerical simulations, this research systematically evaluates the thermal impacts of various greening strategies, including current conditions, lawns, shrubs, and tree configurations with different canopy coverages and leaf area indexes. During summer afternoon heat episodes, the highest temperatures within the building-dense sites were recorded in unshaded open areas, reaching 31.6 °C with a UTCI of 43.95 °C. While green shading provided some cooling, the contribution of natural ventilation was more significant (shrubs and lawns reduced temperatures by 0.23 °C and 0.15 °C on average, respectively, whereas various tree planting schemes yielded minimal reductions of only 0.012–0.015 °C). Consequently, this study proposes a climate-adaptive sustainable design paradigm: in areas aligned with the prevailing sea breeze, lower tree coverage should be maintained to create ventilation corridors that maximize passive cooling through natural wind resources; conversely, in densely built areas with continuous urban interfaces, higher tree coverage is essential to enhance shading and reduce solar radiant heat loads. Full article

Coastal flooding risk is intensifying under climate change, especially along the low sandy Senegalese coastline. This study explores the spatiotemporal variability of extreme coastal water levels (ECWL) from 1993 to 2023 by combining ERA5 reanalysis (waves, wind, pressure), tide gauge and meteorological data, and applying a generalized Pareto distribution (GPD) to estimate the 99th percentile and return levels for 50 and 100 year events. The analysis of the upper 1% of ECWLs reveals significant spatial heterogeneity: 99th percentile values exceed 1.2 m in the Dakar region (Yoff, Ouakam, Ngor) and around Saint-Louis/Langue de Barbarie, with 95% confidence intervals ranging from approximately 1.15 m to 1.30 m, while Casamance and the Saloum Delta exhibit much lower extremes (0.8–1.0 m). For return periods, ECWLs vary between 1.6 m and 2.3 m, with the 100 year return level (T100) exceeding 2.25 m in Dakar, above 2.0 m in Saint-Louis, and intermediate values (1.5–1.9 m) along the Petite Côte (Mbour–Toubab Dialaw) and in the Saloum Delta. The 50 year return level (T50) follows a similar spatial pattern but is 5–10 cm lower than T100 in the most exposed areas. Sensitivity analysis shows that ECWLs are primarily controlled by astronomical tide along much of the coast, whereas wave runup dominates in the southern estuarine zones (Saloum, Casamance, Mbour). Trend analysis using the Mann–Kendall test reveals a latitudinal gradient: stronger positive slopes in the south, weaker trends in central and northern sections, but all p values lie between 0.1 and 0.4, meaning none of the trends reach conventional significance. These findings point to a potential intensification of extreme water levels in socio-economically critical areas (Dakar, Saint-Louis, Mbour) but should be interpreted with caution given the lack of robust statistical significance. The results provide a quantitative basis for coastal risk management in light of projected sea level rise. Full article

As the hydrogen economy rapidly expands, carbon-fiber-reinforced polymer composites (Towpreg) have become key materials for next-generation hydrogen pressure vessels, offering superior processability, reproducibility, and storage stability compared to conventional wet-winding composites. Since hydrogen storage vessels are evaluated at three representative service temperatures (−40, 25, and 85 °C), Towpreg materials must maintain consistent mechanical performance across this range to meet certification standards. This study establishes an integrated methodology combining Towpreg panel fabrication, temperature-controlled tensile and fatigue testing, and quantitative assessment of thermo-mechanical stability using DM epoxy resin as the matrix. To address artifacts such as tab slippage at high temperatures and inefficiency at low temperatures, a “Localized Thermal Control” approach was developed. The HY-Mini Heater System enables localized heating at 85 °C, while the HY-Cooler System applies a Joule–Thomson-based Stirling cooler for efficient localized cooling at −40 °C. Quantitative evaluation showed tensile strengths of 2973.3 MPa (RT), 2767.3 MPa (HT, ~7% decrease), and 2907.7 MPa (LT, ~2% decrease). Under R = 0.1 fatigue testing, the Basquin slope (m) was 11.97 (RT), 9.98 (HT), and 10.6 (LT), while the intercept (log b ≈ 3.7) remained nearly constant. These results confirm the excellent thermo-mechanical stability of the carbon-fiber-reinforced polymer composites (Towpreg) for hydrogen tank applications. Full article

Persistent forest fire refugia are areas within fire-prone landscapes that remain fire-free over long periods of time and are crucial for ecosystem resilience. Modelling to develop maps of these refugia is key to informing fire and land use management. We predict persistent forest fire refugia using variables linked to the fire triangle (aspect, slope, elevation, topographic wetness, convergence and roughness, solar irradiation, temperature, surface wind direction, and speed) in machine learning algorithms (Random Forest, XGBoost; two ensemble models) and K-Nearest Neighbour. All models were run with and without ADASYN over-sampling and grid search hyperparameterisation. Six iterations were run per algorithm to assess the impact of omitting variables. Aspect is twice as influential as any other variable across all models. Solar radiation and surface wind direction are also highlighted, although the order of importance differs between algorithms. The predominant importance of aspect relates to solar radiation received by sun-facing slopes and resultant heat and moisture balances and, in this study area, the predominant fire wind direction. Ensemble models consistently produced the most accurate results. The findings highlight the importance of topographic and microclimatic variables in persistent forest fire refugia prediction, with ensemble machine learning providing reliable forecasting frameworks. Full article

Low-altitude palaeoglaciation in Atlantic mountain regions provides important insights into past climatic conditions and moisture dynamics during the Last Glacial Cycle. This study presents the first quantitative reconstruction of palaeoglaciers in Serra da Cabreira (northwest Portugal), a mid-altitude granite massif located along the Atlantic fringe of the Iberian Peninsula. Detailed geomorphological mapping (1:14,000) and field surveys identified 48 glacial and periglacial landforms, enabling reconstruction of two small valley glaciers in the Gaviões and Azevedas valleys using GlaRe numerical modelling. The spatial distribution of palaeoglacial landforms shows a pronounced west–east asymmetry: periglacial features prevail on wind-exposed west-facing slopes, whereas glacial erosion and depositional landforms characterise the more protected east-facing valleys. The reconstructed glaciers covered 0.24–0.98 km², with maximum ice thicknesses of 72–89 m. Equilibrium-line altitudes were estimated using AABR, AAR, and MELM methods, yielding consistent palaeo-ELA values of ~1020–1080 m. These results indicate temperature depressions of ~6–10 °C and enhanced winter precipitation associated with humid, Atlantic-dominated conditions. Comparison with regional ELA datasets situates Cabreira within a clear Atlantic–continentality gradient across northwest Iberia, aligning with other low-altitude maritime palaeoglaciers in the northwest Iberian mountains. The findings highlight the strong influence of the orographic barrier position, moisture availability, valley hypsometry, and structural controls in sustaining small, climatically sensitive glaciers at low elevations. Serra da Cabreira thus provides a key reference for understanding Last Glacial Cycle palaeoclimatic variability along the Western Iberian margin. Full article

Dunes are key geomorphological features controlling airflow and sediment transport. While these processes are well documented under onshore conditions, this study provides the first high-resolution spatial analysis of dune-beach dynamics under offshore winds, integrating wind flow, sediment transport, and topographic data. The investigated site is a low-elevation (<1 m) dune typical of Mediterranean coasts, characterized by a mixed sand–gravel patch and a distinct beach slope break. Results show that dune height strongly controls the magnitude of airflow adjustment. Directional deflections and accelerations remain limited (<15° and <40%, respectively), and the sheltered zone extends only to the downwind dune toe. During strong wind events (gusts > 50%), sediment transport initiates immediately beyond the crest, feeding offshore-directed fluxes. Under weaker winds (gusts < 20%), enhanced surface roughness from the mixed sand–gravel patch and flow stagnation at the slope break shift the active transport zone toward the lower beach, where the most pronounced morphological changes occur. These findings demonstrate that small dunes provide limited aerodynamic shelter and fail to prevent sediment export under offshore winds. They highlight the need to incorporate additional factors (e.g., microtopography, surface properties) when assessing sediment budgets and the long-term evolution of low-relief coastal systems. Full article

Acoustic sensing is a passive and cost-effective option for unmanned aerial vehicle detection, where both signal processing and microphone hardware jointly determine field performance. In this study, we focus on the hardware front-end as a foundation for improving the reliability of subsequent DSP- or AI-based detection methods. We present a detection-focused comparison of several microphones in outdoor tests, combining calibrated range measurements with spectral analysis of real unmanned aerial vehicle emissions from three platforms. We report hardware metrics only: signal-to-noise ratio, effective detection range, attenuation slope with distance, and the low-frequency background floor. Across wind conditions and source orientations, the RØDE NTG-2 with WS6 windshield delivered the most balanced performance: in strong wind, it extended the detection range over the bare NTG-2 by approximately 31–131% (depending on azimuth), lowered the low-frequency noise floor by about 2–3 decibels, and matched or increased the wideband signal-to-noise ratio by 1.8–4.4 decibels. A parabolic NTG-2 achieved very low background noise levels at low frequencies and strong on-axis reach but proved vulnerable to gust-induced transients. Based on this evidence, we propose an eight-channel, dual-tier array of NTG-2 + WS6 elements that preserves near-hemispherical coverage and phase coherence, establishing a practical hardware baseline for outdoor acoustic unmanned aerial vehicle detection and a reproducible platform for subsequent localization and classification studies. Full article