Atmosphere

29 pages, 21749 KB

Open AccessArticle

Spatiotemporal Dynamics and Impact Mechanism of Heatwave Exposure in the Urban Elderly Population Across China

by Ying Jiang, Tao Gao, Zhenyu Hu and Zhaofei Xu

Atmosphere 2025, 16(12), 1339; https://doi.org/10.3390/atmos16121339 - 26 Nov 2025

Heatwaves are intensifying across China under global warming. Although previous SSP-RCP studies project more frequent and intense events, systematic evaluations of exposure mechanisms among the elderly in China remain limited. The purpose of the paper is to reveal the spatiotemporal dynamics and inequality [...] Read more.

Heatwaves are intensifying across China under global warming. Although previous SSP-RCP studies project more frequent and intense events, systematic evaluations of exposure mechanisms among the elderly in China remain limited. The purpose of the paper is to reveal the spatiotemporal dynamics and inequality of heatwave exposure among China’s urban elderly and to disentangle the driving influences of climate change, ageing, and urbanization. Historical and future heatwaves across China are identified and analyzed, exposure inequality is evaluated using the Gini coefficient, and the relative contributions of key drivers are quantified through factor separation. Results showed that heatwave frequency and duration increased from 2000 to 2019, with high-risk provinces clustering in the Yangtze River Basin, North China Plain, and Sichuan Basin. Future projections indicate substantial growth in elderly exposure to heatwaves, while under the SSP3-70 scenario, inter-provincial inequality in exposure tends to alleviate rather than intensify. Climate change was identified as the dominant driver, while ageing amplified risks and urbanization partly mitigated growth. These findings highlighted the urgent need for place-based adaptation and health protection strategies, aligned with climate mitigation, demographic transition, and sustainable urban planning. Full article

(This article belongs to the Section Biometeorology and Bioclimatology)

28 pages, 7795 KB

Open AccessArticle

The Vertical Development of Fog in the Presence of Turbulent Mixing and Low Stratus Cloud Using Infra-Red Imagery During the SOFOG3D Campaign

by Jenna Thornton, Jeremy Price, Frederic Burnet and Julien Delanoë

Atmosphere 2025, 16(12), 1338; https://doi.org/10.3390/atmos16121338 - 26 Nov 2025

Abstract

Observations made using infra-red cameras as part of the South-west FOGs 3D experiment (SOFOG3D) have been used to analyse the dynamics and evolution of radiation fog in the presence of turbulent-mixing at fog top. The imagery revealed that mixing between the fog and [...] Read more.

Observations made using infra-red cameras as part of the South-west FOGs 3D experiment (SOFOG3D) have been used to analyse the dynamics and evolution of radiation fog in the presence of turbulent-mixing at fog top. The imagery revealed that mixing between the fog and the air above was common, appearing in over 80% of the radiation-fog cases analysed. The mixing often took the form of sections of fog breaking-off and dissipating in the air above; occasionally, these break-away sections did not dissipate but instead became very low cloud elevated above the fog layer. We have found that the mixing between the fog and air above can lead to an increase in relative humidity (RH) and enhanced cooling above the fog layer. Once the RH above the fog reaches within a few percentage points from saturation, it appears that the air mixed up from the fog below can remain saturated, and the fog may then rapidly grow vertically. Therefore, the turbulent-mixing observed can influence cloud coverage via both the vertical development of existing fog and the ‘spawning’ of very-low-stratus cloud. Full article

(This article belongs to the Section Atmospheric Techniques, Instruments, and Modeling)

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24 pages, 4423 KB

Open AccessArticle

Influence of Engine Load on Soot Mass Concentration and Morphology in Diesel Exhaust

by Iliyan Damyanov, Evgeni Dimitrov, Hristo Konakchiev and Iliyan Ognyanov

Atmosphere 2025, 16(12), 1336; https://doi.org/10.3390/atmos16121336 - 26 Nov 2025

Abstract

This study investigates the relationship between exhaust gas composition, particle number (PN) emissions, and soot microstructure of a 1.9 L compression-ignition engine operated under six controlled steady-state load regimes at 2000 min⁻¹. Unlike standardized transient procedures (e.g., WLTP), the steady-state approach [...] Read more.

This study investigates the relationship between exhaust gas composition, particle number (PN) emissions, and soot microstructure of a 1.9 L compression-ignition engine operated under six controlled steady-state load regimes at 2000 min⁻¹. Unlike standardized transient procedures (e.g., WLTP), the steady-state approach enables isolation and quantification of fundamental thermochemical processes governing soot formation and NO_x production, providing engine-out data highly relevant for understanding Euro 7 emission behavior at the source. The novel contributions of this study include (i) a combined macroscopic–microscopic analysis linking PN emissions with SEM/EDS-based soot morphology; (ii) distribution-based estimation of soot mass concentration using experimentally derived primary particle sizes; and (iii) an experimental demonstration of the NO_x–soot trade-off across increasing load, supported by microstructural evidence of soot oxidation and agglomeration. The results show a clear decrease in PN concentrations with increasing load (from 1.31 × 10⁷ to 6.4 × 10⁶ cm⁻³), accompanied by a marked rise in NO_x emissions and exhaust temperature. SEM analysis confirms a transition from fine, weakly agglomerated soot structures at low load to more compact, oxidized aggregates at high load. Distribution-based particle sizing (20–80 nm, average ~45 nm) yields soot mass estimates that are consistent with theoretical trends and more accurate than fixed-radius approaches. These findings provide experimentally supported insights into engine-out particulate behavior that complements regulatory PN metrics in Euro 7, offering a mechanistic basis for improved emission control strategies and for interpreting PN-focused regulatory thresholds under real-world operating conditions. Full article

(This article belongs to the Special Issue Vehicle Emissions Testing, Modeling, and Lifecycle Assessment)

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21 pages, 1677 KB

Open AccessArticle

Assessment of Lightning Activity and Early Warning Capability Using Near-Real-Time Monitoring Data in Hanoi, Vietnam

by Hoang Hai Son, Nguyen Xuan Anh, Tran Hong Thai, Pham Xuan Thanh, Pham Le Khuong, Hiep Van Nguyen, Do Ngoc Thuy, Bui Ngoc Minh, Nguyen Nhu Vinh, Duong Quang Ve, Hung Mai Khanh, Dang Dinh Quan and Tien Du Duc

Atmosphere 2025, 16(12), 1335; https://doi.org/10.3390/atmos16121335 - 26 Nov 2025

Abstract

This study investigates lightning activity and evaluates a near-real-time lightning warning system for the inner Hanoi area, using data collected during 2020–2024 from the Strike Guard (SG) and EFM-100C instruments located in Chuong My, Hanoi, Vietnam. Lightning detection data were incorporated with rainfall [...] Read more.

This study investigates lightning activity and evaluates a near-real-time lightning warning system for the inner Hanoi area, using data collected during 2020–2024 from the Strike Guard (SG) and EFM-100C instruments located in Chuong My, Hanoi, Vietnam. Lightning detection data were incorporated with rainfall and lightning location information from the Vietnam Meteorological and Hydrological Administration (VNMHA) for quality checking. The SG data over the research area revealed clear diurnal and seasonal variations, with lightning most frequent in the late afternoon and two major peaks in June and September corresponding to the summer monsoon. A combined warning method using EFM-100C electric field measurements and SG alert states achieved an average lead time of 15 min, a Probability of Detection (POD) of 82.22%, a Critical Success Index (CSI) of 76.55%, an F1 score of 86.72%, and a False Alarm Ratio (FAR) of 8.26%. These results demonstrate that integrating electric field and optical–electromagnetic measurements can provide effective localized lightning warnings for the urban areas. The approach is cost-efficient, operationally feasible, and particularly valuable for protecting critical infrastructure regions, supporting enhanced lightning safety and disaster mitigation in northern Vietnam. Full article

(This article belongs to the Section Meteorology)

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20 pages, 1673 KB

Open AccessArticle

Air Quality Index Forecasting Based on Quadratic Decomposition and Transformer-BiLSTM—A Case Study of Beijing

by Peng Cheng, Chuanning Wei, Jinhua Zhang and Haizheng Wang

Atmosphere 2025, 16(12), 1334; https://doi.org/10.3390/atmos16121334 - 25 Nov 2025

Abstract

Accurate Air Quality Index (AQI) forecasting is crucial for environmental pollution control. However, the strong nonlinearity and pronounced non-stationarity of AQI time series limit the precision of single-model predictions. This paper therefore proposes an efficient new AQI forecasting model. First, the raw AQI [...] Read more.

Accurate Air Quality Index (AQI) forecasting is crucial for environmental pollution control. However, the strong nonlinearity and pronounced non-stationarity of AQI time series limit the precision of single-model predictions. This paper therefore proposes an efficient new AQI forecasting model. First, the raw AQI sequence is decomposed using Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN). This is combined with Sample Entropy (SE) and K-means clustering to reconstruct high-, medium-, and low-frequency sub-sequences. For the high-frequency component, a second decomposition is performed using Variational Mode Decomposition (VMD) optimised by the Crested Porcupine Optimizer (CPO). This forms the basis for constructing a hybrid forecasting model: the CEEMDAN–SE–CPO–VMD–Transformer-BiLSTM model. Finally, the prediction error is corrected via Least Squares Support Vector Machine (LSSVM). Empirical analysis based on AQI data of Beijing in summer 2023 demonstrates that this model significantly outperforms traditional models and single-decomposition models in terms of MAE, RMSE, MAPE, and R² metrics. Cross-seasonal experiments further confirm its excellent predictive performance and robustness across the spring, autumn, and winter. This model provides a new, efficient, and reliable approach for AQI forecasting. Full article

(This article belongs to the Section Air Quality)

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31 pages, 5514 KB

Open AccessArticle

Hydro-Climatic and Multi-Temporal Remote Analysis of Glacier and Moraine Lake Changes in the Ile-Alatau Mountains (1955–2024), Northern Tien Shan

by Gulnara Iskaliyeva, Aibek Merekeyev, Nurmakhambet Sydyk, Alima Azamatkyzy Amangeldi, Bauyrzhan Abishev and Zhaksybek Baygurin

Atmosphere 2025, 16(12), 1333; https://doi.org/10.3390/atmos16121333 - 25 Nov 2025

Abstract

High-mountain regions such as the Ile-Alatau range of the Northern Tien Shan are highly sensitive to climatic fluctuations, where even minor variations in temperature and precipitation significantly influence glacier mass balance and hydrology. Despite this sensitivity, few long-term studies have examined the links [...] Read more.

High-mountain regions such as the Ile-Alatau range of the Northern Tien Shan are highly sensitive to climatic fluctuations, where even minor variations in temperature and precipitation significantly influence glacier mass balance and hydrology. Despite this sensitivity, few long-term studies have examined the links between hydro-climatic trends, glacier retreat, and moraine lake development. This study investigates multi-decadal glacier and lake dynamics (1955–2024) in relation to observed climate variability, using an integrated hydro-climatic and remote-sensing approach. Temperature and precipitation records from four high-altitude meteorological stations were assessed using linear regression and the Mann–Kendall test, while glacier and lake extents were derived from aerial photographs and Landsat, Sentinel-2, and PlanetScope imagery across ten river basins. Results show statistically significant warming at all stations, with mean annual temperatures increasing by 0.14–0.28 °C per decade and summer temperatures by 0.15–0.30 °C, while precipitation remained stable or slightly decreased. Glacierized area decreased from approximately 269.6 km² in 1955 to 141.7 km² in 2021, representing a 47.4% reduction (≈−0.72% yr⁻¹) over six decades and underscoring the rapid regional cryospheric response to sustained climatic warming. Simultaneously, moraine-dammed lakes increased by 16–18% between 2017 and 2024. These trends highlight the dominant climatic control on glacier loss and lake evolution, emphasizing growing glacial lake outburst floods (GLOFs) and the need for adaptive water-resource management in Central Asia. Full article

(This article belongs to the Special Issue Glacier Mass Balance and Variability)

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32 pages, 1374 KB

Open AccessArticle

Long-Term Temperature and Precipitation Trends Across South America, Urban Centers, and Brazilian Biomes

by José Roberto Rozante, Gabriela Rozante and Iracema Fonseca de Albuquerque Cavalcanti

Atmosphere 2025, 16(12), 1332; https://doi.org/10.3390/atmos16121332 - 25 Nov 2025

Abstract

This study examines long-term trends in maximum (Tmax) and minimum (Tmin) near-surface air temperatures and precipitation across South America, focusing on Brazilian biomes and national capitals, using ERA5 reanalysis data for 1979–2024. To isolate the underlying climate signal, seasonal cycles were removed using [...] Read more.

This study examines long-term trends in maximum (Tmax) and minimum (Tmin) near-surface air temperatures and precipitation across South America, focusing on Brazilian biomes and national capitals, using ERA5 reanalysis data for 1979–2024. To isolate the underlying climate signal, seasonal cycles were removed using Seasonal-Trend decomposition based on Loess (STL), which effectively separates short-term variability from long-term trends. Temperature trends were quantified using ordinary least squares (OLS) regression, allowing consistent estimation of linear changes over time, while precipitation trends were assessed using the non-parametric Mann–Kendall test combined with Theil–Sen slope estimation, a robust approach that minimizes the influence of outliers and serial correlation in hydroclimatic data. Results indicate widespread but spatially heterogeneous warming, with Tmax increasing faster than Tmin, consistent with reduced cloudiness and evaporative cooling. A meridional precipitation dipole is evident, with drying across the Cerrado, Pantanal, Caatinga, and Pampa, contrasted by rainfall increases in northern South America linked to ITCZ shifts. The Pantanal emerges as the most vulnerable biome, showing strong warming (+0.51 °C decade⁻¹) and the steepest rainfall decline (–10.45 mm decade⁻¹). Satellite-based fire detections (2013–2024) reveal rising wildfire activity in the Amazon, Pantanal, and Cerrado, aligning with the “hotter and drier” climate regime. In the capitals, persistent Tmax increases suggest enhanced urban heat island effects, with implications for public health and energy demand. Although ERA5 provides coherent spatial coverage, regional biases and sparse in situ observations introduce uncertainties, particularly in the Amazon and Andes, these do not alter the principal finding that the magnitude and persistence of the 1979–2024 warming lie well above the range of interdecadal variability typically associated with the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO). This provides strong evidence that the recent warming is not cyclical but reflects the externally forced secular warming signal. These findings underscore growing fire risk, ecosystem stress, and urban vulnerability, highlighting the urgency of targeted adaptation and resilience strategies under accelerating climate change. Full article

(This article belongs to the Special Issue Hydroclimate Extremes Under Climate Change)

12 pages, 1198 KB

Open AccessArticle

Regional and Whole-Body Dermal Emission Rates of Volatile Sulfur Compounds and Potential Impact on Indoor Air Odour

by Tomomi Osaka, Daisuke Sato, Akihiro Hosomi, Mizuki Fukui and Yoshika Sekine

Atmosphere 2025, 16(12), 1331; https://doi.org/10.3390/atmos16121331 - 25 Nov 2025

Abstract

Volatile sulfur compounds (VSCs) are known to cause characteristic—and sometimes unpleasant—body odour. Human presence may influence the odour of indoor air; however, the contribution of skin-derived VSCs has not been thoroughly evaluated. This study aimed to elucidate the regional and whole-body dermal emission [...] Read more.

Volatile sulfur compounds (VSCs) are known to cause characteristic—and sometimes unpleasant—body odour. Human presence may influence the odour of indoor air; however, the contribution of skin-derived VSCs has not been thoroughly evaluated. This study aimed to elucidate the regional and whole-body dermal emission rates of VSCs—diallyl disulfide (DADS), allyl methyl sulfide (AMS), ethyl mercaptan (EMT), allyl mercaptan (AMT) and dimethyl trisulfide (DMTS)—by conducting simultaneous and multi-point measurements of dermal emissions from the human skin surface to assess their potential impact on indoor air quality. Dermal emission fluxes of VSCs were measured at 14 anatomical regions of 12 healthy young subjects using a passive flux sampler coupled with gas chromatography/mass spectrometry. These fluxes were converted to emission rates using regional body surface area, and the whole-body emission rates were subsequently used to estimate indoor air concentrations for comparison with the odour thresholds of each VSC. The results showed that although some regional differences in emission rates were observed among subjects, the large inter-individual variability ultimately led to no significant differences in whole-body emission rates of VSCs between males and females. Using the average whole-body emission rates across 12 subjects, the estimated indoor air concentrations of VSCs followed the descending order: EMT > AMT >> DMTS > AMS > DADS. The odour quotient was used to evaluate the impact of skin-derived VSCs on indoor air quality and indicated that EMT consistently contributes to indoor odour. Full article

(This article belongs to the Special Issue Advances in Integrated Air Quality Management: Emissions, Monitoring, Modelling (4th Edition))

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32 pages, 3525 KB

Open AccessArticle

Discovery of Regular Daily Ionospheric Scintillation

by Janis Balodis, Madara Normand and Ingus Mitrofanovs

Atmosphere 2025, 16(12), 1330; https://doi.org/10.3390/atmos16121330 - 25 Nov 2025

Abstract

The aim of this study was to find out whether, just like in March 2015, daily regular GPS positioning disturbances caused by ionospheric scintillations occurred in other months of the solar activity cycle 24. The GPS positioning 90-s kinematic solutions of selected 46 [...] Read more.

The aim of this study was to find out whether, just like in March 2015, daily regular GPS positioning disturbances caused by ionospheric scintillations occurred in other months of the solar activity cycle 24. The GPS positioning 90-s kinematic solutions of selected 46 months covering 11 years were used to search for regular daily scintillation events. The hypothesis on predictable regular daily ionospheric scintillation was tested. Scintillation waves were discovered as a result of space weather impact with the sidereal day regularity. It leads to the conclusion that the radiation originates from the interplanetary medium. The enhancement of radiation waves by solar activity is similar to Pc1 waves. The regular daily ionospheric scintillation waves are recorded at any time of the day. In the years with low solar activity in 2010 and 2012, regular scintillation waves were not found. It cannot be claimed that the comparison of daily regular ionospheric scintillation cases over time with the mentioned Pc1 wave cases indicates any interrelation. Full article

(This article belongs to the Special Issue Geomagnetic Storms and Their Consequences: Advances in Prediction Models)

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32 pages, 19448 KB

Open AccessArticle

Sensitivity of Atmospheric Energetics to Optically Thin Ice Clouds During the Arctic Polar Night

by Housseyni Sankaré, Jean-Pierre Blanchet and René Laprise

Atmosphere 2025, 16(12), 1329; https://doi.org/10.3390/atmos16121329 - 24 Nov 2025

Abstract

Cloud feedback is a major source of uncertainty in climate projections. In particular, Arctic clouds, arguably one of the most poorly understood aspects of the climate system, strongly modulate radiative energy fluxes from the Earth’s surface to the top of the atmosphere. In [...] Read more.

Cloud feedback is a major source of uncertainty in climate projections. In particular, Arctic clouds, arguably one of the most poorly understood aspects of the climate system, strongly modulate radiative energy fluxes from the Earth’s surface to the top of the atmosphere. In situ and satellite observations reveal the existence of ubiquitous optically thin ice clouds (TICs) in the Arctic during polar nights, whose influence on atmospheric energy is still poorly understood. This study quantifies the effect of TICs on the atmospheric energy budget during polar winter. A reanalysis-driven simulation based on the Canadian Regional Climate Model version 6 (CRCM6) was used with the Predicted Particle Properties (P3) scheme (2016) to produce an ensemble of 3 km mesh simulations. This set is composed of three simulations: CRCM6 (reference, the original dynamically coupled cloud formation), CRCM6 (nocld) (clear-sky) and CRCM6 (100%cld) (overcast, 100% cloud cover as a forcing perturbation). Using the regional energetic equations (Nikiema and Laprise), we compare the three cases to assess TIC forcing. The results show that TICs cool the atmosphere, with the difference between two simulations (cloud/no clouds) reaching up to −2 K/day, leading to a decrease in temperature on the order of ~−4 KMonth⁻¹. The energetics cycle indicates that the time-mean enthalpy generation term G_M and baroclinic conversion dominate Arctic circulation. The G_M acting on the available enthalpy reservoir (A_M) increased by a maximum value of ~5 W·m⁻² (58% on average) due to the effects of TICs, increasing in energy conversion. TICs also lead to average changes of 9% in time-mean available enthalpy and −5.9% in time-mean kinetic energy. Our work offers valuable insights into the Arctic winter atmosphere and provides the means to characterize clouds for radiative transfer calculations, to design measurement instruments, and to understand their climate feedback. Full article

(This article belongs to the Section Meteorology)

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27 pages, 14639 KB

Open AccessArticle

Towards Understanding Earthquake Preparatory Dynamics: A Multi-Parametric Investigation of the 2025 Kamchatka Mw 8.8 Event

by Sudipta Sasmal, Kousik Nanda, Masashi Hayakawa, Maria Solovieva, Galina Kopylova and Stelios M. Potirakis

Atmosphere 2025, 16(12), 1328; https://doi.org/10.3390/atmos16121328 - 24 Nov 2025

Abstract

We present a comprehensive multi-parametric analysis of Lithosphere– Atmosphere–Ionosphere Coupling (LAIC) processes associated with the M = 8.8 earthquake that struck offshore Kamchatka, Russia, on 30 July 2025 (29 July 2015; 23:24:52 UTC). Thermal observations revealed coherent pre-seismic irregularities in near-surface air temperature, [...] Read more.

We present a comprehensive multi-parametric analysis of Lithosphere– Atmosphere–Ionosphere Coupling (LAIC) processes associated with the M = 8.8 earthquake that struck offshore Kamchatka, Russia, on 30 July 2025 (29 July 2015; 23:24:52 UTC). Thermal observations revealed coherent pre-seismic irregularities in near-surface air temperature, relative humidity, and atmospheric chemical potential (ACP), with maximum intensification occurring 1–2 days before the event, followed by rapid co-seismic dissipation and post-seismic recovery. Acoustic channel analysis revealed considerable enhancements in atmospheric gravity wave (AGW) potential energy, as computed from ERA5 reanalysis datasets, 3–5 days prior to the earthquake, with a co-seismic peak and weaker post-seismic irregularities at higher altitudes. Electromagnetic signatures manifested in both lower and upper ionospheric layers. Very-Low-Frequency (VLF) sub-ionospheric propagation from the NPM transmitter, continuously monitored at the PTK (Petropavlovsk-Kamchatsky) station in Kamchatka, Russia, exhibited both positive and negative deviations in amplitude and phase during the preparatory phase. VLF amplitude exhibited wavelike deviations consistent with AGW periods, peaking one day prior to the earthquake. Ionospheric Vertical Total electron content (VTEC) showed coherent pre-seismic maxima 2–3 days before the main shock. Together, these thermal, acoustic, and electromagnetic observations strongly suggest a consistent pre-seismic build-up, co-seismic dissipation, and post-seismic recovery, providing a robust multi-channel imprint of the Kamchatka earthquake and highlighting the importance of integrated multi-parameter approaches for understanding earthquake preparatory dynamics. Full article

(This article belongs to the Section Upper Atmosphere)

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22 pages, 4374 KB

Open AccessArticle

Drivers and Future Regimes of Runoff and Hydrological Drought in a Critical Tributary of the Yellow River Under Climate Change

by Yu Wang, Yong Wang, Wenya Fang, Yuhan Zhao, Ying Zhou and Fangting Wang

Atmosphere 2025, 16(12), 1327; https://doi.org/10.3390/atmos16121327 - 24 Nov 2025

Abstract

China’s Yellow River basin encounters widespread risks of reduced runoff and intensified hydrological drought. This study focuses on the middle and upper reaches of the Dahei River, the Yellow River’s primary tributary. In this region, the Soil & Water Assessment Tool (SWAT) hydrological [...] Read more.

China’s Yellow River basin encounters widespread risks of reduced runoff and intensified hydrological drought. This study focuses on the middle and upper reaches of the Dahei River, the Yellow River’s primary tributary. In this region, the Soil & Water Assessment Tool (SWAT) hydrological model was employed to simulate hydrological processes, identify runoff changes and hydrological drought characteristics, and conduct attribution analysis from 1983 to 2022, as well as to project trends over the next 40 years. The results indicate that total runoff during the impact period (1999–2022) decreased by 55.26% compared to the baseline period (1983–1998). Climate change accounted for a contribution rate of 38.6% to this decline, while human activities accounted for 61.4%. Additionally, climate primarily altered surface runoff (SURQ) and lateral groundwater flow (LATQ) through precipitation changes, while land use had a predominant influence on total runoff volume by modifying SURQ. Both factors exhibited relatively minor effects on LATQ. Moreover, human activities contribute to hydrological drought at a rate of 36.11% to 94.25%. Drought probability is significantly influenced by climate through precipitation and temperature changes, while land use primarily mitigates hydrological drought by impacting the three runoff components. It is predicted that over the next 40 years, total runoff will decrease by 2.08% to 60.16%, along with hydrological droughts that are more frequent, longer in average duration, and more intense; however, the Maximum Drought Duration is anticipated to shorten. In the east and northeast, hydrological drought presents a trend of intensification, with central and western regions exhibiting weaker or declining changes. Full article

(This article belongs to the Special Issue The Response of Plateau Vegetation to Climatic and Anthropogenic Drivers)

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21 pages, 7051 KB

Open AccessArticle

Inter-Monthly Variations in CO₂ and CH₄ Fluxes in a Temperate Forest: Coupling Dynamics and Environmental Drivers

by Chuying Guo, Fuxi Ke, Leiming Zhang and Shenggong Li

Atmosphere 2025, 16(12), 1326; https://doi.org/10.3390/atmos16121326 - 24 Nov 2025

Abstract

Climate change, driven largely by anthropogenic greenhouse gas emissions, is a major global issue. Long-term high-frequency measurements of gas fluxes remain limited, especially outside the growing season. This study addresses two key gaps: the absence of continuous annual data capturing diurnal and seasonal [...] Read more.

Climate change, driven largely by anthropogenic greenhouse gas emissions, is a major global issue. Long-term high-frequency measurements of gas fluxes remain limited, especially outside the growing season. This study addresses two key gaps: the absence of continuous annual data capturing diurnal and seasonal variations, and the biases from suboptimal sampling timing. Using automated chambers, we monitored soil CO₂ and CH₄ fluxes throughout 2016 in a temperate forest on Changbai Mountain, China. Our results showed a strong negative correlation between annual CO₂ and CH₄ fluxes, with a slope of −0.21 and R² of 0.70. This relationship persisted from March to November but was absent during the winter and April. Both gases exhibited the largest diurnal variations in summer. Statistical analysis identified 16:00 as the optimal single sampling time for estimating daily mean fluxes in most months. CO₂ fluxes were primarily governed by temperature but modulated by VWC (soil volumetric water content). They were suppressed during summer drought and enhanced during winter freeze–thaw cycles. CH₄ uptake rates were strongly dependent on VWC throughout the growing season, while their temperature response underwent a reversal from positive in summer to negative in winter. Decision tree analysis revealed nonlinear threshold responses. CO₂ fluxes exhibited three temperature thresholds between 5.30 and 15.64 °C and two VWC thresholds between 0.30 and 0.42 m³ m⁻³. CH₄ fluxes showed five temperature thresholds ranging from 2.34 to 15.71 °C and seven VWC thresholds from 0.11 to 0.44 m³ m⁻³. The strongest anticorrelation between CH₄ flux and temperature occurred at intermediate VWC levels. This study provides detailed characteristics of greenhouse gas fluxes based on complete annual high-frequency data. It emphasizes the importance of year-round monitoring and offers improved sampling strategies and mechanistic insights for better flux monitoring and climate prediction. Full article

(This article belongs to the Topic Ecosystems and Climate Change: Understanding Impacts to Shape the Future)

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22 pages, 3366 KB

Open AccessArticle

Leveraging Meteorological Reanalysis Models to Characterize Wintertime Cold Air Pool Events Across the Western United States from 2000 to 2022

by Jacob Boomsma and Heather A. Holmes

Atmosphere 2025, 16(12), 1325; https://doi.org/10.3390/atmos16121325 - 24 Nov 2025

Abstract

Wintertime cold air pools (CAPs) are common across the Western United States and result in cold, dense air trapped in valley basins. The CAPs are characterized by a stable atmospheric boundary layer, leading to cold air and low wind speeds. While CAP formation [...] Read more.

Wintertime cold air pools (CAPs) are common across the Western United States and result in cold, dense air trapped in valley basins. The CAPs are characterized by a stable atmospheric boundary layer, leading to cold air and low wind speeds. While CAP formation occurs nightly, the CAP conditions can persist into daytime and often last for multiple days (i.e., persistent cold air pool or PCAP), resulting in poor air quality in populated areas. The presence and strength of CAPs can be calculated using data from radiosondes, surface weather stations at varying elevations, and indirectly through air pollution monitors. Because vertical profile data are often limited to twice daily radiosondes, and are spatially sparse, numerical models can be a useful substitute. This work uses the European Centre for Medium-Range Weather Forecasts (ECMWFs) Reanalysis v5 (ERA) atmospheric reanalysis to provide data to classify wintertime CAP events without radiosonde observations. An automated CAP classification method using ERA outputs is evaluated using afternoon radiosonde observations in six cities (Salt Lake City, Utah; Reno, Nevada; Boise, Idaho; Denver, Colorado; Las Vegas, Nevada; Medford, and Oregon). Using this CAP determination method, days with CAP events are analyzed in 13 locations, 6 with radiosonde observations and 7 without, including the Central valley of California. The CAP classification method is evaluated at these 13 locations across the Western US over the study period of 2000–2022. The results show that the ERA model performs similarly to the radiosonde observations when used to identify CAP events. Therefore, ERA can be used to provide a reasonable estimate of CAP conditions when radiosonde data are unavailable. Providing consistent CAP classifications across space and time are necessary for regional scale CAP studies, such as human health effects modeling over large spatial and temporal scales. Full article

(This article belongs to the Section Meteorology)

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19 pages, 9064 KB

Open AccessArticle

Hybrid VMD–BiGRU Framework for Multi-Step Forecasting of PM_2.5 in Traffic-Intensive Cities of the Kingdom of Saudi Arabia

by Afaq Khattak, Saleh Alotaibi, Raed Nayif Alahmadi, Caroline Mongina Matara and Sami Taglawi

Atmosphere 2025, 16(12), 1324; https://doi.org/10.3390/atmos16121324 - 24 Nov 2025

Abstract

Fine particulate matter (PM_2.5) poses major public health and environmental threats due to its capacity to enter deep respiratory passages and degrade urban air quality. In the Kingdom of Saudi Arabia (KSA), cities such as Riyadh, Dammam, and Jeddah show an [...] Read more.

Fine particulate matter (PM_2.5) poses major public health and environmental threats due to its capacity to enter deep respiratory passages and degrade urban air quality. In the Kingdom of Saudi Arabia (KSA), cities such as Riyadh, Dammam, and Jeddah show an elevated level of PM_2.5 due to rapid urban growth, dense traffic activity, and wide industrial operations. This study proposes a hybrid Variational Mode Decomposition–Bidirectional Gated Recurrent Unit (VMD–BiGRU) framework for multi-horizon PM_2.5 forecasts based on daily data from January 2022 to September 2024. The daily PM_2.5 series was split through VMD into Intrinsic Mode Functions (IMFs) that represent multi-scale temporal patterns. A seven-day ahead forecast was carried out, and model performance was compared with VMD–GRU, VMD–LSTM, and VMD–TCN. For Riyadh, RMSE values for t + 1, t + 2, and t + 3 were 9.25, 12.26, and 16.05 µg/m³, with R² above 0.90 up to the third day. For Dammam, RMSE values for the same horizons were 4.46, 7.24, and 11.34 µg/m³, and R² remained above 0.90 up to the fourth day. For Jeddah, the corresponding values were 3.97, 6.09, and 9.36 µg/m³, and R² remained above 0.90 up to the fourth day. The hybrid VMD–BiGRU model achieved higher accuracy for short horizons (t + 1 to t + 3). The study establishes a basis that aids short-term PM_2.5 prediction and improves air quality assessment across major urban centers in KSA. Full article

(This article belongs to the Section Air Quality)

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13 pages, 2827 KB

Open AccessArticle

Study on Atmospheric Boundary Layer Retrieval Method and Observation Data Analysis Based on Aerosol Lidar

by Chao Chen, Bingao Sui, Zhangjun Wang, Baoqing Sun, Hui Li, Xin Pan, Guoliang Shentu, Quanfeng Zhuang, Xianxin Li, Hao Chen and Wenbo Jiang

Atmosphere 2025, 16(12), 1323; https://doi.org/10.3390/atmos16121323 - 23 Nov 2025

Abstract

The atmospheric boundary layer is the lowest part of the troposphere, directly influenced by the Earth’s surface. The boundary layer’s height is a critical parameter for weather forecasting, air quality monitoring, and climate modeling. Lidar has become a premier tool for continuous boundary [...] Read more.

The atmospheric boundary layer is the lowest part of the troposphere, directly influenced by the Earth’s surface. The boundary layer’s height is a critical parameter for weather forecasting, air quality monitoring, and climate modeling. Lidar has become a premier tool for continuous boundary layer height detection with its high spatial–temporal resolution. A multi-wavelength aerosol lidar with 355 nm, 532 nm, and 1064 nm has been developed and deployed for operational observations at the Haidian District Meteorological Service of Beijing. The structure design, specifications, observation campaign, and detection principle of the multi-wavelength aerosol lidar are presented and the retrieval method of the boundary layer’s height is introduced. By comparing it with the data of the digital radiosonde, it is verified that the first normalized gradient of the range-corrected signal can more accurately retrieve the boundary layer’s height. The typical daily variation characteristics and influencing factors of urban boundary layer height are analyzed through observational examples and the monthly mean value of the boundary layer’s height in 2019 is acquired and analyzed. Full article

(This article belongs to the Special Issue Data Analysis and Algorithms for Aerosols Remote Sensing)

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12 pages, 3143 KB

Open AccessArticle

Fire-Enhanced Soil Carbon Sequestration in Wetlands: A 5000-Year Record from the Ussuri River, Northeast China

by Yan Zhao, Xinyuan He and Zhenqing Zhang

Atmosphere 2025, 16(12), 1322; https://doi.org/10.3390/atmos16121322 - 23 Nov 2025

Abstract

Using high-resolution charcoal and TOC records from a sediment core collected in a coastal wetland along the middle reaches of the Ussuri River, the local fire history and carbon accumulation patterns were reconstructed for the past 5000 years. Results indicate that fire intensity [...] Read more.

Using high-resolution charcoal and TOC records from a sediment core collected in a coastal wetland along the middle reaches of the Ussuri River, the local fire history and carbon accumulation patterns were reconstructed for the past 5000 years. Results indicate that fire intensity remained relatively low and stable from 5000 to 1500 cal. yr BP, after which it increased markedly. This trend intensified over the past 400 years, likely due to rapid population growth and heightened anthropogenic disturbance. Regional fire frequency averaged approximately 3.1 fires per 1500 years, with notable peaks during 5000–4600 cal. yr BP, 3400–2400 cal. yr BP, and 1500 cal. yr BP to present. These high-fire intervals correspond closely to regional warm and dry climatic conditions, underscoring the strong influence of climate variability on fire activity. Carbon accumulation rates also showed a significant increase, rising from 0.11 g·kg⁻¹·a⁻¹ around 5000 years ago to 1.60 g·kg⁻¹·a⁻¹ in recent centuries. Importantly, a significant positive correlation was observed between fire regimes and carbon accumulation rates, suggesting that fires have potentially played a key role in enhancing long-term carbon sequestration in wetlands of this region. These findings highlight the complex interplay between fire, climate, and carbon dynamics in wetland ecosystems. Full article

(This article belongs to the Special Issue The Evolution of Climate and Environment in the Holocene)

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37 pages, 6640 KB

Open AccessArticle

Bridging Heritage Conservation and Energy Efficiency: Retrofitting Historic Social Housing in Mediterranean Cities

by Zoe Kanetaki, Evgenia Tousi, Athina Mela, Eleni Kanetaki, Gianluca Pappaccogli and Emmanouel Proestakis

Atmosphere 2025, 16(12), 1321; https://doi.org/10.3390/atmos16121321 - 23 Nov 2025

Abstract

Historic social housing in Mediterranean cities faces the dual challenges of energy inefficiency and cultural preservation. This study presents a pilot methodological framework for energy retrofitting of historical residence buildings, using the Kaisariani Asia Minor refugee housing complex in Athens as a case [...] Read more.

Historic social housing in Mediterranean cities faces the dual challenges of energy inefficiency and cultural preservation. This study presents a pilot methodological framework for energy retrofitting of historical residence buildings, using the Kaisariani Asia Minor refugee housing complex in Athens as a case study. A bibliometric analysis revealed a research gap, as clusters concerning heritage retrofitting and social housing remain weakly connected, highlighting limited interdisciplinary integration between cultural conservation and energy-efficient design. The proposed framework combines historical analysis, energy consumption assessment, and technical evaluation to examine three retrofit scenarios that integrate thermal insulation, upgraded HVAC systems, renewable domestic hot water, and photovoltaic installations. Results demonstrate that substantial performance improvements can be achieved without compromising architectural authenticity. The most comprehensive scenario achieved a 97% reduction in primary energy demand, a 63–76% decrease in heating and cooling loads, and significant CO₂ emission reductions, maintaining economic feasibility with a payback period of approximately ten years. The findings emphasize that conservation-compatible retrofitting can transform obsolete housing into low-energy buildings, fostering environmental, social, and cultural sustainability. Beyond quantitative energy gains, the study underlines the importance of integrating heritage values and community identity into urban regeneration strategies, offering a transferable model for Mediterranean municipalities seeking to align climate action with cultural continuity. Full article

(This article belongs to the Special Issue Advanced Studies on Climate Change in Urban Areas: Emerging Technologies and Strategies to Address Heat Waves and Improve Thermo-Hygrometric Comfort)

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13 pages, 9263 KB

Open AccessArticle

Modulation of the Semi-Annual Oscillation by Stratospheric Sudden Warmings as Seen in the High-Altitude JAWARA Re-analyses

by Jiarong Zhang, Yvan Orsolini and Kaoru Sato

Atmosphere 2025, 16(12), 1320; https://doi.org/10.3390/atmos16121320 - 23 Nov 2025

Abstract

The semi-annual oscillation (SAO) dominates seasonal variability in the equatorial stratosphere and mesosphere. However, the seasonally dependent modulation of the SAO in the stratosphere (SSAO) and mesosphere (MSAO) by sudden stratospheric warmings (SSWs) in the Arctic has not been investigated in detail. In [...] Read more.

The semi-annual oscillation (SAO) dominates seasonal variability in the equatorial stratosphere and mesosphere. However, the seasonally dependent modulation of the SAO in the stratosphere (SSAO) and mesosphere (MSAO) by sudden stratospheric warmings (SSWs) in the Arctic has not been investigated in detail. In this study, we examine the seasonal evolution of the SAO during 16 major SSW events spanning 2004 to 2024 using the Japanese Atmospheric General Circulation Model for Upper Atmosphere Research Data Assimilation System Whole Neutral Atmosphere Re-analysis (JAWARA). Basic features of the SAO are well captured by JAWARA, as evidenced by the SSAO and MSAO appearing at around 50 km and 85 km, respectively. The different responses of the SAO to early and late winter SSWs are particularly strong during the Northern Hemisphere winter of 2023/24. Early winter SSWs tend to significantly intensify the westward SSAO, while late winter SSWs tend to weaken the eastward SSAO. Similarly, the eastward MSAO is amplified during early winter SSWs, whereas the westward MSAO is slightly weakened during late winter SSWs. The weak MSAO response is probably due to its smaller climatological magnitude. Modulation of the SAO by SSWs is related to meridional temperature changes during SSWs through the thermal wind balance. Our findings contribute to the understanding of coupling between the tropics and high latitudes, as well as interhemispheric coupling. Full article

(This article belongs to the Special Issue Observations and Analysis of Upper Atmosphere (2nd Edition))

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