Multiscale Dynamics and Climatic Drivers of Aircraft Icing in China: Insights from 13 Years of Pilot Reports (2011-2023)

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This study leverages China's first public 13-year (2011–2023) pilot reports (PIREPs) and multi-source data to elucidate the spatiotemporal dynamics and climatic drivers of icing across China. Key findings reveal: (1) a distinct southwest-high, east-moderate, northwest-low spatial pattern driven by topography, aviation density, and regional climate; (2) vertical stratification with peak occurrence at 2–8 km, governed by moisture-temperature coupling at mid-low altitudes (2–6 km) and jet stream uplift at higher levels (> 7.5 km); (3) winter frequency surpasses summer by 7.3 times, with a significant post-2018 ascent of the primary icing layer at ~ 500 m a − 1 , strongly linked to rising freezing levels under global warming; (4) divergent regional mechanisms - frontal systems and aerosols in North China, terrain-trapped moisture in the Sichuan Basin, and ocean-jet stream interactions along coasts. These insights underpin region-specific warning strategies (targeting mid-altitude fronts, low-altitude terrain zones, and upper-level jets) and advance climate-resilient aviation meteorology through improved risk management. Earth and environmental sciences/Climate sciences Earth and environmental sciences/Environmental sciences Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Aircraft icing refers to the phenomenon where ice layers accumulate on the cold surfaces of an aircraft when it traverses clouds containing supercooled water droplets, due to contact between the droplets and the fuselage 1 . It is one of the critical meteorological hazards threatening flight safety 2 , 3 . The physical mechanisms and spatiotemporal evolution of icing have long been a core focus in aviation meteorology research 4 , 5 . Icing poses multifaceted threats to flight safety by altering aerodynamic performance 6 or triggering control system failures 7 , with risks being particularly pronounced during low-speed and low-altitude climb and approach phases 3 . Despite the widespread installation of anti-icing systems on modern aircraft, icing-related accidents remain frequent globally 8 – 10 , underscoring the persistent severity of this issue. Icing events are subject to multidimensional influences from meteorological conditions and human activities. Observational studies demonstrate that icing can occur at altitudes of 0–8000 m 11 and temperatures between − 30 to 0°C 12 , with nearly half of events concentrated within the − 12 to − 8°C range and the 1500–4000 m altitude. Urban heat island effects and industrial emissions during urbanization may enhance supercooled water content and induce icing 4 by altering local atmospheric stratification stability 13 , 14 . Notably, the increasing frequency of extreme weather events under global warming is reshaping the environmental background fields of icing occurrence 15 , 16 , further amplifying prediction uncertainties. In numerical modeling, Thompson et al 17 demonstrated that models often underestimate the presence of supercooled water 18 , and icing is significantly influenced by topographic features, which are softened in low-resolution models 4 . Notably, while current literature predominantly employs case-specific methodologies, a critical gap remains in long-term systematic investigation of physical mechanisms. Furthermore, current research on aircraft icing remains predominantly focused on Europe and North America. However, as the world's second-largest civil aviation passenger market 19 , China suffers from a severe mismatch between its icing research depth and aviation scale while confronting more complex challenges: (1) significant topographic mechanism differentiation, where China’s three-tiered terrain ( Tibetan Plateau > Sichuan Basin > Eastern Plains ) profoundly alters unique regional circulation and water vapor transport through thermal-dynamic processes 20 , unlike the relatively uniform terrain of Europe and North America, resulting in fundamentally distinct icing formation mechanisms; (2) a weak observational system, since icing data relies heavily on Pilot Reports (PIREPs) without a standardized detection network, and existing studies are mostly short-term cases that hinder mechanism validation and model development; and (3) imbalanced risk distribution, with eastern airports handling 4.7 times more cargo volume than western ones 19 , yet 94% of events in the low-frequency Northwest region reach moderate-to-severe intensity, exhibiting a ‘low-frequency but high-impact’ pattern rarely observed in Europe and North America. This study utilizes first-hand icing data from Chinese pilot reports (PIREPs) spanning 2011–2023, integrated with multi-source meteorological data, to address three key objectives: (1) identification of multi-scale spatiotemporal differentiation characteristics; (2) elucidation of thermodynamic-dynamic coupling mechanisms governing supercooled water generation; and (3) quantification of the altitudinal migration response of icing risk heights under climate warming. The findings aim to provide theoretical support for optimizing aviation meteorological warning systems and revising airworthiness standards, offering critical implications for enhancing flight safety. 2. Method and Materials This study conducts a multi-scale spatiotemporal characteristic analysis of aircraft icing based on pilot reports (PIREPs) from China between 2011 and 2023. The raw data underwent rigorous screening to remove duplicate and ambiguous records, resulting in 5,779 valid samples for analysis. Pilot reports (PIREPs) refer to critical weather information reported by pilots via radio to Air Traffic Control (ATC) authorities when encountering significant weather phenomena (e.g., icing, turbulence, wind shear) that impact flight safety during operations. These reports are subsequently relayed by ATC to meteorological forecasters. PIREPs not only provide real-time warnings for subsequent flights but also assist ATC in optimizing aircraft command strategies and supply ground-truth validation data for forecasters. The data collection scope of this study encompasses all airspace sectors within mainland China. According to the Notice on the Implementation of Electronic Entry and Dissemination of Voice-Based Aircraft In-Flight Reports issued by the CAAC Air Traffic Management Bureau in 2017, regional meteorological centers or aeronautical meteorological offices (stations) must standardize the entry of PIREPs relayed by air traffic control (ATC) authorities using predefined templates. Required fields include flight number, aircraft type, hazardous weather type, intensity, occurrence time, location information, and impact on flight operations. Overall, icing intensity records are categorized into four classes: weak, moderate, strong, and unknown. It is worth noting that although PIREPs provide real-time hazard reports, potential underreporting of light icing events may occur due to pilots' subjective assessment. This limitation primarily affects weak-intensity statistics but has a minimal impact on moderate/severe events dominating this study (97.7% of total). 3. Results and Discussion 3.1 Spatial Differentiation and Multi-Scale Drivers of Aircraft Icing Events in China The spatial distribution of icing events in China from 2011 to 2023 exhibits significant heterogeneity (Fig. 1 a). Statistical data reveal that the annual average number of icing events per province is approximately 10, with a cumulative mean of 130 events. Notably, Sichuan Province recorded the highest national total of 906 events (annual average of 69.7), accounting for 22.5% of all cases, while Hebei Province reported the lowest cumulative frequency of 5 events. The regional distribution demonstrates a gradient pattern of "high-frequency in the southwest, moderate in the east, and low-frequency in the northwest," which is closely coupled with China's geographical environment and aviation activity intensity 5 . As the core high-frequency zone of icing, Southwest China’s formation mechanisms can be attributed to topographic-meteorological synergy: The Sichuan Basin and surrounding mountains enhance vertical motion through topographic uplift 21 (Wang et al., 2025), combined with abundant moisture transport 22 , creating a sustained supercooled water enrichment environment 23 . Eastern coastal provinces, Guangdong (264 events), Shanghai (260 events), and Zhejiang (244 events) collectively account for 19% of the national total, with their high-frequency patterns directly linked to intensive aviation activity. CAAC statistics 19 indicate that cargo and mail throughput at airports in this region is 4.7 times that of western China. Simultaneously, abundant moisture flux in monsoon regions 24 and localized circulation adjustments induced by urban heat island effects 13 , 14 jointly establish the thermodynamic-dynamic conditions for icing occurrence. The northern regions experienced significantly fewer icing events, with the three northeastern provinces recording a cumulative total of only 113 instances (accounting for < 3% of the national total). This is closely related to winter low temperatures inhibiting the formation of supercooled water and lower aviation traffic. However, it should be noted that winter frontal activities can still cause sudden icing risks. Although the annual average frequency in northwestern regions (such as Xinjiang and Gansu) remains relatively low, moderate-to-severe events account for 94.3–97.9% of occurrences, indicating that their icing processes exhibit more sudden and high-intensity characteristics. Moderate-to-severe icing events (Fig. 1 b) account for 97.7% of the total, highlighting the high-risk nature of icing hazards in China. The Sichuan Basin, with a cumulative total of 902 events, tops the list, validating the amplifying effect of topographic forcing on icing intensity 5 . Although the eastern coastal regions exhibit higher frequency, there are significant intensity variations: Guangdong and Shanghai report 100% and 99.6% moderate-to-severe events, respectively, while Zhejiang stands at 90.6%, reflecting regional heterogeneity in meteorological responses. Notably, nine provinces, including Hubei and Fujian, have an annual average of only 4 events, yet 100% of these are moderate-to-severe, indicating that icing risks in low-frequency areas exhibit a 'low-frequency but high-impact' characteristic. In summary, the spatial heterogeneity of icing in China is governed by three mechanisms: (1) aviation activity intensity, with flight density in economic core zones showing a significant positive correlation with icing frequency 19 ; (2) terrain-climate synergy, where southwestern mountainous areas sustain persistent icing environments through dynamic uplift and moisture convergence, while the eastern monsoon region relies on abrupt moisture flux changes to trigger events; (3) human activity interference, as urban heat islands and industrial emissions alter local atmospheric stratification, increasing icing probability 4 . This distribution pattern holds critical implications for air route planning and meteorological warnings, requiring differentiated strategies that prioritize routine risks in high-frequency zones and sudden threats in low-frequency areas. 3.2 Vertical Heterogeneity Characteristics and Multi-Mechanism Coupling Effects of Aircraft Icing Events in China The vertical distribution of icing events in China from 2011 to 2023 exhibits significant stratification dependence (Fig. 2 a). Statistics reveal that icing events are concentrated at altitudes of 2–8 km, accounting for 89.6% of the total. Among these, the 3.5–4 km altitude layer accumulated 787 instances (peak zone), followed by 5–5.5 km and 6–6.5 km layers with 739 and 673 instances, respectively. Notably, moderate-to-severe icing events accounted for 66.8% (526 instances) in the 3.5–4 km layer, with risk severity displaying a bimodal vertical pattern: aside from the primary peak, the 7.5–8.5 km layer accumulated 587 instances, representing 22.4% of severe cases. This phenomenon is closely tied to thermodynamic-dynamic conditions at different altitudes: moisture convergence and temperature gradients jointly sustain supercooled water enrichment at mid-to-low levels (2–6 km) 18 , 21 , while jet stream dynamic uplift at higher altitudes (> 7.5 km) triggers supercooled water generation at deep convective cloud tops. Further analysis of regional differences (Fig. 2 b) reveals that the vertical distribution of icing events across provinces is significantly modulated by geographical climate and circulation systems: In the Sichuan Basin, 280 icing events (30.9% of the province’s total) occurred at 2–4 km altitude, attributed to the basin’s terrain trapping low-level moisture 25 . The specific humidity at 2–4 km remains above 5 g/kg year-round 26 , combined with adiabatic cooling from topographic uplift, creating a persistent supercooled water environment. In Guangdong and the South China Sea region, 112 events (42.4% of the province’s total) were concentrated at 8–10 km, distinct from inland provinces. This unique high-altitude icing mechanism arises from the synergy between deep convective cloud top expansion driven by tropical weather systems, dynamic uplift from subtropical jet streams 24 , and high-altitude moisture transport under maritime climate conditions. In the North China Plain, the 4–6 km layer is the primary icing zone (e.g., Beijing with 27 events), where mid-level cloud system development during winter cold front passages and ice-nucleating effects from industrial aerosols 13 jointly enhance supercooled water generation. Though the 8–10 km layer accounts for a high proportion of events in the southwestern plateau (e.g., 85% in Tibet), total occurrences are less than 10% of those in humid regions, reflecting the fundamental constraint of scant moisture on icing over the plateau 21 , 27 . The vertical heterogeneity of icing highlights the prominence of dual risk layers at mid-to-low altitudes (2–4 km and 5–6 km), which collectively account for 71.3% of national icing events. The former is dominated by topographic forcing and moisture convergence, while the latter is linked to frontal system uplift and urban aerosol effects 14 . Additionally, high-altitude sudden-risk zones (7.5–9.5 km) are primarily distributed in eastern coastal areas like Guangdong and Shanghai, associated with tropical cyclone anvils and sudden supercooled water enrichment in jet stream zones 7 . Although such events represent only 18.5% of cases, their safety threat is heightened due to the difficulty of real-time avoidance during cruising phases. From an aviation meteorological management perspective, these vertical characteristics hold critical guidance for flight-phase risk mitigation: During climb/approach phases ( 8 km), enhance icing monitoring and warnings in high-altitude jet stream zones over the South China Sea and eastern coast. Regionally, the North China Plain should prioritize monitoring mid-altitude frontal cloud systems in winter, while the southwestern plateau requires vigilance against sudden high-altitude icing under moisture-scarce conditions. The findings not only elucidate the physical mechanisms of vertical icing distribution but also provide a scientific basis for developing differentiated early-warning strategies. 3.3 Temporal Evolution Characteristics and Climate Response of Aircraft Icing Events in China The temporal evolution of aircraft icing events in Chinese airspace from 2011 to 2023 exhibits multi-scale coupled characteristics (Fig. 3 a). In terms of icing intensity distribution, moderate and above events (Moderate+) accounted for 77.6% of total records, with Moderate, Moderate-Severe, and Severe categories contributing 47.2%, 6.5%, and 23.9%, respectively, underscoring the high-risk nature of icing events in Chinese airspace 28 . These events have been directly linked to multiple major aviation incidents in recent years 8 , 10 , making their temporal heterogeneity critical for in-depth analysis. On an interannual scale, the altitude of icing events shows a significant upward trend: before 2017, primary occurrence layers concentrated in 2000–4000 m (peak at 3000–4000 m, 150 annual average events), while post-2018 saw a rise at 500 m a − 1 (Fig. 3 b). This phenomenon correlates closely with the rising atmospheric freezing level under climate warming 29 and enhanced vertical moisture transport driven by frequent extreme weather 15 , 16 . As shown in Supplementary Fig. 1, temperatures in East Asia’s 2–6 km layer increased by 0.8–1.2°C and specific humidity rose by 10–15% during 2011–2023, directly promoting the expansion of high-altitude supercooled water generation conditions. On seasonal scales, icing events exhibit extreme temporal concentration. Winter (DJF) monthly averages reached 847 events, 7.3 times higher than summer (JJA, 116.6 events/month), with December, January, and February accumulating 818, 950, and 774 events, respectively (Fig. 3 c). Vertically, winter icing primarily occurred in 2000–4000 m (68% of cases), but 21% of events were observed at 4000–6500 m, reflecting seasonal synergy between frontal systems and high-altitude jet streams 11 , 30 . Notably, icing altitudes follow an inverted-V annual pattern: the main occurrence layer rises from 3000 m in January to 4500 m by April, then retreats below 2500 m from July to September (Fig. 3 d), aligning with seasonal adjustments in East Asian monsoon thermal-moisture vertical profiles 10 . At hourly resolution, icing frequency strongly couples with flight scheduling 31 and diurnal temperature-humidity cycles 32 : events remain below 100/h from 01:00–06:00, surge post-06:00, peak at 10:00 (> 400/h), and sustain high levels through the afternoon (12:00–18:00) (Fig. 3 e). However, the proportion of moderate-to-severe events decreases by 15% -20% during 09:00–21:00, potentially due to daytime turbulence accelerating supercooled droplet collision-freezing 32 or temperature rises inhibiting sustained icing 8 . In summary, the temporal heterogeneity of icing events in China results from the synergistic interplay between natural climate change and human activities. Climate warming reshapes the vertical distribution of icing by elevating freezing level altitudes, while the increasing frequency of extreme weather intensifies seasonal and diurnal variability. Concurrently, increasing aviation traffic (e.g., during peak daytime hours) amplifies the temporal clustering of icing risks. These findings underscore that future aviation meteorological warnings must prioritize: (1) core mid-to-low altitude icing zones in winter, (2) climate-warming-driven expansion of high-altitude risk belts, and (3) sudden events during daytime flight-intensive periods. This framework provides theoretical support for dynamic risk management strategies. 3.4 Meteorological Driving Mechanisms and Regional Heterogeneity of Aircraft Icing Events in China The occurrence of aircraft icing events in China exhibits significant regional heterogeneity in meteorological conditions, driven by the synergy of atmospheric circulation patterns, vertical thermal-moisture distributions, and cloud microphysical processes (Supplementary Fig. 2). Under macro-circulation regimes, winter’s 'two-trough-one-ridge' structure in the 500 hPa geopotential height field governs frontal-type icing formation in North China: the Northeast Cold Vortex interacts with troughs extending southward to the North China Plain, where mid-upper-level north westerlies transport cold air, low-level shear lines trigger moisture convergence, and surface cold fronts generate deep cloud systems 33 . Persistent cold advection from north westerlies at 700 hPa and 850 hPa, combined with enhanced near-surface moisture convergence via 1000 hPa shear flows (Supplementary Fig. 2d), jointly establish thermodynamic-dynamic conditions for frontal icing. In Beijing, icing events peak at 8–10 km altitude (annual average of 100 events), with moderate-to-severe cases comprising 25–30% in the 6–10 km layer (Supplementary Fig. 3). This altitude range maintains stable temperatures of -12°C to -2°C (corresponding to 720–555 hPa) and relative humidity of 45.8–55.8% (Fig.S4). Industrial aerosols in North China (e.g., black carbon and sulfate) enhance ice-nucleating particle (INP) concentrations at 4–6 km altitudes, potentially elevating supercooled water occurrence. Wu et al. demonstrated that assimilating real-time aerosol data improves supercooled water prediction accuracy by 22–40% in this region 34 . Although quantitative correlations between INPs and icing frequency require further observation-model integration, the persistent co-occurrence of high aerosol loading and moderate-to-severe icing events (Fig. S3) suggests aerosol microphysical effects likely amplify icing risks. The icing mechanisms in the Sichuan Basin are governed by dual influences of topographic locking and modulation by the southern branch trough (Fig. 4 ). At 500 hPa, the southern branch trough of the westerlies drives warm, moist southwestern airflow into the basin, where it converges with post-trough cold air, creating a stratified instability with cold upper and warm lower layers. At 700 hPa, the Tibetan High synergizes with convergent basin wind fields to trigger warm-moist air uplift. Within the 2–4 km layer, specific humidity reaches 5 g/kg, and cloud liquid water content attains 0.4–0.5 g/kg (Figs. 4 c-d). Coupled with low temperatures (-3°C to -8°C), these conditions drive mixed-phase ice formation exceeding 60%, yielding an annual average of 39 icing events (75.7% of the total). This underscores the pivotal role of topographic dynamics in moisture retention 25 . Notably, while events at 8–10 km altitudes are less frequent, moderate-to-severe cases constitute 30%, emphasizing the need to concurrently address sudden high-altitude risks. The icing mechanisms in eastern coastal regions reflect the interaction between subtropical jet streams and maritime climate (Fig. 5 ). At 500 hPa, the westerly jet (16 m/s) and pre-trough southwestern airflow jointly transport warm-moist air. At 700 hPa, enhanced southwesterlies boost moisture flux, while 850 hPa shear lines trigger low-level convergence. In the Yangtze River Delta region, temperatures at 5–7 km range from − 6°C to -12°C with cloud water content of 0.1–0.2 g/kg, where the subtropical jet prolongs supercooled droplet persistence 35 . Climate warming has driven an annual average rise of 120 m in the 0°C isotherm, shifting icing risks toward 5–7 km. In Guangdong, high-altitude (8–10 km) temperatures range from − 15°C to -25°C, but the South China Sea monsoon induces localized moisture enrichment (0.05–0.1 g/kg) at convective cloud tops. Coupled with strong updrafts suppressing ice nucleation, this results in an annual average of 112 icing events—a mechanism distinct from inland regions. From the cloud microphysical perspective (Figs. 4 – 5 , S4), the supercooled droplet formation altitudes (3–6 km) align vertically with the core icing event layers. Beijing's 4–6 km layer exhibits cloud water content of 0.2–0.3 g/kg, where low-temperature conditions (-5 to -10°C) promote glaze ice formation. In the Sichuan Basin, synergistic effects between high humidity (> 80%) at 2–4 km and orographic uplift enhance droplet collision efficiency. Although the 5–7 km layer over eastern coastal regions shows lower cloud water content, jet stream-driven dynamical uplift delays supercooled water freezing. This vertical configuration divergence reveals that orographic dynamics dominate moisture enrichment for inland icing, while maritime climates coupled with jet stream modulation shape elevated risks in coastal zones. These differentiated characteristics provide explicit guidance for aviation meteorological warnings: North China requires focused attention on mid-level frontal cloud systems during cold front passages, Sichuan Basin should prioritize enhanced low-altitude monitoring in topographically enclosed areas, Eastern coastal regions need to establish high-altitude warning thresholds tailored for jet stream zones. Under climate warming, the vertical migration trends of icing risk layers (e.g., increasing frequency at high altitudes in Guangdong) must be integrated into dynamic risk assessment frameworks. 4. Conclusion Aircraft icing events in China exhibit pronounced spatial gradients, with high-incidence zones concentrated in the southwestern region (annual average of 69.7 events) and eastern coastal areas (19% of total incidents), jointly driven by orographic dynamics and aviation activity intensity. Although the northwestern region experiences lower frequencies, over 94% of its events reach moderate-to-severe intensity, demonstrating a "low-frequency, high-impact" risk profile. Vertically, icing events predominantly occur between 2–8 km altitude: low-to-mid levels (2–6 km) are governed by moisture convergence, while upper layers (> 7.5 km) rely on jet stream-induced dynamical uplift, revealing synergistic regulation by terrain and atmospheric circulation. Temporally, winter (DJF) icing frequency surpasses summer by 7.3 times, with the primary icing layer ascending at 500 m/year since 2018, closely linked to rising atmospheric freezing levels and intensified moisture transport under climate warming. Regionally, North China’s frontal icing is driven by the "two-trough-one-ridge" circulation pattern and cold front intrusions, exacerbated by mid-altitude cloud development and industrial aerosol ice nucleation effects. The Sichuan Basin experiences persistent warm-moisture advection via the southern branch trough and topographic confinement, where low-altitude high humidity (specific humidity > 5 g/kg) elevates mixed-phase ice prevalence (> 60%). Coastal regions exhibit distinct high-altitude supercooled water enrichment mechanisms regulated by subtropical jet streams and the South China Sea monsoon. Cloud microphysical analyses confirm vertical alignment between supercooled droplet formation heights (3–6 km) and icing core layers, with inland terrain-forced moisture configurations contrasting sharply with marine-influenced coastal vertical distributions. Proposed region-specific warning strategies include: monitoring mid-altitude frontal cloud systems in North China, enhancing low-altitude surveillance in Sichuan, and establishing high-altitude jet stream thresholds for coastal areas. Climate warming necessitates dynamic assessment of icing layer vertical migration trends (e.g., increasing high-altitude events in Guangdong). Study limitations involve subjectivity in Pilot Reports (PIREPs) and insufficient precision in local meteorological simulations. Future efforts should integrate multi-source observations (satellite retrievals, airborne sensors) with high-resolution numerical models to develop a multi-scale prediction framework for aircraft icing across China. Declarations Data availability The ERA5 reanalysis data were downloaded from https://www.ecmwf.int/en/forecasts/dataset/ecmwf-reanalysis-v5. Acknowledgements This work was supported by National Key Research and Development Program of China (No. 2022YFC3002502), National Natural Science Foundation of China (NSFC) Excellent Young Scientists Fund (No. 42422506), the National Natural Science Foundation of China (No. 42275122), and the National Key Scientific and Technological Infrastructure project “Earth System Science Numerical Simulator Facility” (EarthLab). Ting Yang would like to express gratitude towards the Program of the Youth Innovation Promotion Association (CAS). Author information Authors and Affiliations 1. Nanjing University of Aeronautics and Astronautics Wei Zhang, Minhua Hu, 2. State Key Laboratory of Atmospheric Environment and Extreme Meteorology, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China Ting Yang, Yining Tan, Shiyu Zhang, Liang Li, Yutong Tian, 3. Aviation Meteorological Center of the Air Traffic Management Bureau, Civil Aviation Administration of China, Beijing, China Wei Zhang, Tong Lv, Chongyu Zhang, Hongtai Zhang, Sisi Gao Contributions Conceptualization: Ting Yang, Wei Zhang. Formal analysis: Yining Tan, Shiyu Zhang, Liang Li, Yutong Tian. Funding acquisition: Ting Yang. Investigation: Minhua Hu Methodology: Wei Zhang. Project administration: Ting Yang. Resources: Wei Zhang. Software: Yining Tan, Shiyu Zhang, Liang Li, Yutong Tian. Supervision: Ting Yang, Wei Zhang, Minhua Hu. Validation: Tong Lv, Chongyu Zhang, Hongtai Zhang, Sisi Gao, Yining Tan. Visualization: Yining Tan, Shiyu Zhang, Liang Li, Yutong Tian, Writing, original draft: Ting Yang, Yining Tan, Shiyu Zhang, Liang Li, Yutong Tian. 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Journal of Geophysical Research : Atmospheres, 129, e2023JD039671 (2024). Roy, P., Rauber, R., Di Girolamo, L. Evolution of cloud droplet temperature and lifetime in spatiotemporally varying subsaturated environments with implications for ice nucleation at cloud edges. Atmospheric Chemistry and Physics , 24, 11653–11672 (2024). Additional Declarations No competing interests reported. Supplementary Files Supplement.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6902239","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":475199897,"identity":"a8285cc2-d634-456b-9625-a83c66c010f7","order_by":0,"name":"WEI Zhang","email":"","orcid":"","institution":"Nanjing University of Aeronautics and Astronautics","correspondingAuthor":false,"prefix":"","firstName":"WEI","middleName":"","lastName":"Zhang","suffix":""},{"id":475199898,"identity":"19dd1bad-1e92-4315-940c-9d80d9274aef","order_by":1,"name":"Tong Lv","email":"","orcid":"","institution":"Aviation Meteorological Center of the Air Traffic Management Bureau, Civil Aviation Administration of China","correspondingAuthor":false,"prefix":"","firstName":"Tong","middleName":"","lastName":"Lv","suffix":""},{"id":475199899,"identity":"e92ad417-5e56-488a-a2c8-5f8cfe19daf9","order_by":2,"name":"Sisi Gao","email":"","orcid":"","institution":"Aviation Meteorological Center of the Air Traffic Management Bureau, Civil Aviation Administration of China","correspondingAuthor":false,"prefix":"","firstName":"Sisi","middleName":"","lastName":"Gao","suffix":""},{"id":475199900,"identity":"6a4cbbf0-fe94-41ca-be17-6858b0165763","order_by":3,"name":"Liang Li","email":"","orcid":"","institution":"Institute of Atmospheric Physics, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Liang","middleName":"","lastName":"Li","suffix":""},{"id":475199901,"identity":"8acc7633-a644-4f7b-b90e-84ed1d5c0628","order_by":4,"name":"Yining Tan","email":"","orcid":"","institution":"Institute of Atmospheric Physics, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Yining","middleName":"","lastName":"Tan","suffix":""},{"id":475199902,"identity":"e696de97-b33d-47ce-a4d1-ac3155638190","order_by":5,"name":"Shiyu Zhang","email":"","orcid":"","institution":"Institute of Atmospheric Physics, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Shiyu","middleName":"","lastName":"Zhang","suffix":""},{"id":475199903,"identity":"ef194090-ec4f-48e6-ba65-38d547c1b0ff","order_by":6,"name":"Chongyu Zhang","email":"","orcid":"","institution":"Aviation Meteorological Center of the Air Traffic Management Bureau, Civil Aviation Administration of China","correspondingAuthor":false,"prefix":"","firstName":"Chongyu","middleName":"","lastName":"Zhang","suffix":""},{"id":475199904,"identity":"36477d12-2055-4879-ba7d-92f2f5f7f688","order_by":7,"name":"Hongtai Zhang","email":"","orcid":"","institution":"Aviation Meteorological Center of the Air Traffic Management Bureau, Civil Aviation Administration of China","correspondingAuthor":false,"prefix":"","firstName":"Hongtai","middleName":"","lastName":"Zhang","suffix":""},{"id":475199905,"identity":"189c6fc7-86ba-4579-a96c-1e6af03bcf52","order_by":8,"name":"Yutong Tian","email":"","orcid":"","institution":"Institute of Atmospheric Physics, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Yutong","middleName":"","lastName":"Tian","suffix":""},{"id":475199906,"identity":"9516ebce-74a4-4a9a-a271-d1063c80b496","order_by":9,"name":"Minhua Hu","email":"","orcid":"","institution":"Nanjing University of Aeronautics and Astronautics","correspondingAuthor":false,"prefix":"","firstName":"Minhua","middleName":"","lastName":"Hu","suffix":""},{"id":475199907,"identity":"0e422b1f-81bb-4b78-b52b-798888049e67","order_by":10,"name":"Zifa Wang","email":"","orcid":"","institution":"Institute of Atmospheric Physics, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Zifa","middleName":"","lastName":"Wang","suffix":""},{"id":475199908,"identity":"b769ab2b-8749-4130-bb1a-070dff9c6130","order_by":11,"name":"Ting Yang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/klEQVRIiWNgGAWjYDACZijND8QHHjBIENbBA9Mi2QDUkkCUFhjD4ACQSCDGXfbsvIdf89Tcsdt87fBDoC0W8uYMzA8/MNTcweMwvjRrnmPPkrfdTjMAOcxwZwObsQTDsWd4tPCYGfOwHU42u50A1sK44QCDGQNjw2ECWv4dTjaenf4BpMV+wwH2b4S0GD/mbTtsZyCdA7YlccMBHgK2HOYxY5zbdzhB4nZOwYEEA4nknc08xRIJx3BrYe8/Y/zhzbfD9vyz0zd/+FBRZ7udvX3jhw81uLUAAZsUMHISG8BsAyACRW4CPg3AJPPxBzB+4FwD/KpHwSgYBaNgBAIA1fdSQlKUdZsAAAAASUVORK5CYII=","orcid":"","institution":"Institute of Atmospheric Physics, Chinese Academy of Sciences","correspondingAuthor":true,"prefix":"","firstName":"Ting","middleName":"","lastName":"Yang","suffix":""}],"badges":[],"createdAt":"2025-06-16 06:38:33","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6902239/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6902239/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85394995,"identity":"9527b45c-b17a-4fd4-82cb-9b71afdb4940","added_by":"auto","created_at":"2025-06-25 11:05:07","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":894368,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Distribution of aircraft icing events in China from 2011 to 2023. \u003cstrong\u003eb\u003c/strong\u003e Same as a but for moderate or above aircraft icing events.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-6902239/v1/eeb5d4f88018ffe86cd1a694.png"},{"id":85396304,"identity":"f7f1a8dd-ee11-4c47-a815-f694b773cbbb","added_by":"auto","created_at":"2025-06-25 11:13:07","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1109637,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Altitude Distribution of Icing Events. \u003cstrong\u003eb\u003c/strong\u003e Altitude Distribution of Icing Events across Different Regions of China\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-6902239/v1/01af51cbad9835bb1b5b1873.png"},{"id":85396303,"identity":"621df1dc-fb67-4236-98c1-ef7704f4e6da","added_by":"auto","created_at":"2025-06-25 11:13:07","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2257534,"visible":true,"origin":"","legend":"\u003cp\u003eTemporal characteristics of icing events in China, 2011–2023. \u003cstrong\u003ea\u003c/strong\u003e Intensity proportion. \u003cstrong\u003eb\u003c/strong\u003eInterannual altitude variation. \u003cstrong\u003ec\u003c/strong\u003e Monthly mean event count. \u003cstrong\u003ed\u003c/strong\u003e Heatmap of monthly altitude distribution. \u003cstrong\u003ee\u003c/strong\u003e Hourly event distribution.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-6902239/v1/4e8410e25c734e0a17580526.png"},{"id":85394993,"identity":"bfed507a-5de7-4062-b6b7-8f711da820c5","added_by":"auto","created_at":"2025-06-25 11:05:07","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":905126,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e total frequency of moderate and above aircraft icing events changes with height. \u003cstrong\u003eb\u003c/strong\u003e proportion of moderate and above ice accumulation events changes with height. Vertical distribution of \u003cstrong\u003ec\u003c/strong\u003e temperature and \u003cstrong\u003ed\u003c/strong\u003e cloud water content in the Sichuan Basin from 2019 to 2023 during winter.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-6902239/v1/7422ae249ddc6146fe28f6b8.png"},{"id":85394997,"identity":"688abca7-4181-455b-a017-5bbb74b60a01","added_by":"auto","created_at":"2025-06-25 11:05:07","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":903207,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e total frequency of moderate and above aircraft icing events changes with height. \u003cstrong\u003eb\u003c/strong\u003eproportion of moderate and above ice accumulation events changes with height. Vertical distribution of \u003cstrong\u003ec\u003c/strong\u003e temperature and \u003cstrong\u003ed\u003c/strong\u003e cloud water content in eastern coastal region of China from 2019 to 2023 during winter.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-6902239/v1/43565cfba83563adbea95bbe.png"},{"id":91148181,"identity":"5aaae54f-64f1-455c-8cb0-a522c084d632","added_by":"auto","created_at":"2025-09-12 06:43:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7383873,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6902239/v1/c2449dc1-149d-452d-84a6-7406b05f2fe5.pdf"},{"id":85396305,"identity":"49ee3401-e9c1-45b5-930b-6c8cbedf5589","added_by":"auto","created_at":"2025-06-25 11:13:07","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":4201702,"visible":true,"origin":"","legend":"","description":"","filename":"Supplement.docx","url":"https://assets-eu.researchsquare.com/files/rs-6902239/v1/37d244656f98a17fd110561e.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Multiscale Dynamics and Climatic Drivers of Aircraft Icing in China: Insights from 13 Years of Pilot Reports (2011-2023)","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eAircraft icing refers to the phenomenon where ice layers accumulate on the cold surfaces of an aircraft when it traverses clouds containing supercooled water droplets, due to contact between the droplets and the fuselage\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. It is one of the critical meteorological hazards threatening flight safety\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. The physical mechanisms and spatiotemporal evolution of icing have long been a core focus in aviation meteorology research\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Icing poses multifaceted threats to flight safety by altering aerodynamic performance\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e or triggering control system failures\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e, with risks being particularly pronounced during low-speed and low-altitude climb and approach phases\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. Despite the widespread installation of anti-icing systems on modern aircraft, icing-related accidents remain frequent globally\u003csup\u003e\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e, underscoring the persistent severity of this issue.\u003c/p\u003e \u003cp\u003eIcing events are subject to multidimensional influences from meteorological conditions and human activities. Observational studies demonstrate that icing can occur at altitudes of 0\u0026ndash;8000 m\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e and temperatures between \u0026minus;\u0026thinsp;30 to 0\u0026deg;C\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e, with nearly half of events concentrated within the \u0026minus;\u0026thinsp;12 to \u0026minus;\u0026thinsp;8\u0026deg;C range and the 1500\u0026ndash;4000 m altitude. Urban heat island effects and industrial emissions during urbanization may enhance supercooled water content and induce icing\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e by altering local atmospheric stratification stability\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Notably, the increasing frequency of extreme weather events under global warming is reshaping the environmental background fields of icing occurrence\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, further amplifying prediction uncertainties. In numerical modeling, Thompson et al\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e demonstrated that models often underestimate the presence of supercooled water\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, and icing is significantly influenced by topographic features, which are softened in low-resolution models\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Notably, while current literature predominantly employs case-specific methodologies, a critical gap remains in long-term systematic investigation of physical mechanisms.\u003c/p\u003e \u003cp\u003eFurthermore, current research on aircraft icing remains predominantly focused on Europe and North America. However, as the world's second-largest civil aviation passenger market\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, China suffers from a severe mismatch between its icing research depth and aviation scale while confronting more complex challenges: (1) significant topographic mechanism differentiation, where China\u0026rsquo;s three-tiered terrain (\u003cem\u003eTibetan Plateau\u0026thinsp;\u0026gt;\u0026thinsp;Sichuan Basin\u0026thinsp;\u0026gt;\u0026thinsp;Eastern Plains\u003c/em\u003e) profoundly alters unique regional circulation and water vapor transport through thermal-dynamic processes\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, unlike the relatively uniform terrain of Europe and North America, resulting in fundamentally distinct icing formation mechanisms; (2) a weak observational system, since icing data relies heavily on Pilot Reports (PIREPs) without a standardized detection network, and existing studies are mostly short-term cases that hinder mechanism validation and model development; and (3) imbalanced risk distribution, with eastern airports handling 4.7 times more cargo volume than western ones\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, yet 94% of events in the low-frequency Northwest region reach moderate-to-severe intensity, exhibiting a \u0026lsquo;low-frequency but high-impact\u0026rsquo; pattern rarely observed in Europe and North America.\u003c/p\u003e \u003cp\u003eThis study utilizes first-hand icing data from Chinese pilot reports (PIREPs) spanning 2011\u0026ndash;2023, integrated with multi-source meteorological data, to address three key objectives: (1) identification of multi-scale spatiotemporal differentiation characteristics; (2) elucidation of thermodynamic-dynamic coupling mechanisms governing supercooled water generation; and (3) quantification of the altitudinal migration response of icing risk heights under climate warming. The findings aim to provide theoretical support for optimizing aviation meteorological warning systems and revising airworthiness standards, offering critical implications for enhancing flight safety.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"2. Method and Materials","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThis study conducts a multi-scale spatiotemporal characteristic analysis of aircraft icing based on pilot reports (PIREPs) from China between 2011 and 2023. The raw data underwent rigorous screening to remove duplicate and ambiguous records, resulting in 5,779 valid samples for analysis. Pilot reports (PIREPs) refer to critical weather information reported by pilots via radio to Air Traffic Control (ATC) authorities when encountering significant weather phenomena (e.g., icing, turbulence, wind shear) that impact flight safety during operations. These reports are subsequently relayed by ATC to meteorological forecasters. PIREPs not only provide real-time warnings for subsequent flights but also assist ATC in optimizing aircraft command strategies and supply ground-truth validation data for forecasters. The data collection scope of this study encompasses all airspace sectors within mainland China.\u003c/p\u003e \u003cp\u003eAccording to the Notice on the Implementation of Electronic Entry and Dissemination of Voice-Based Aircraft In-Flight Reports issued by the CAAC Air Traffic Management Bureau in 2017, regional meteorological centers or aeronautical meteorological offices (stations) must standardize the entry of PIREPs relayed by air traffic control (ATC) authorities using predefined templates. Required fields include flight number, aircraft type, hazardous weather type, intensity, occurrence time, location information, and impact on flight operations. Overall, icing intensity records are categorized into four classes: weak, moderate, strong, and unknown. It is worth noting that although PIREPs provide real-time hazard reports, potential underreporting of light icing events may occur due to pilots' subjective assessment. This limitation primarily affects weak-intensity statistics but has a minimal impact on moderate/severe events dominating this study (97.7% of total).\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Spatial Differentiation and Multi-Scale Drivers of Aircraft Icing Events in China\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe spatial distribution of icing events in China from 2011 to 2023 exhibits significant heterogeneity (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). Statistical data reveal that the annual average number of icing events per province is approximately 10, with a cumulative mean of 130 events. Notably, Sichuan Province recorded the highest national total of 906 events (annual average of 69.7), accounting for 22.5% of all cases, while Hebei Province reported the lowest cumulative frequency of 5 events. The regional distribution demonstrates a gradient pattern of \"high-frequency in the southwest, moderate in the east, and low-frequency in the northwest,\" which is closely coupled with China's geographical environment and aviation activity intensity\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eAs the core high-frequency zone of icing, Southwest China\u0026rsquo;s formation mechanisms can be attributed to topographic-meteorological synergy: The Sichuan Basin and surrounding mountains enhance vertical motion through topographic uplift\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e (Wang et al., 2025), combined with abundant moisture transport\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e, creating a sustained supercooled water enrichment environment\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Eastern coastal provinces, Guangdong (264 events), Shanghai (260 events), and Zhejiang (244 events) collectively account for 19% of the national total, with their high-frequency patterns directly linked to intensive aviation activity. CAAC statistics\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e indicate that cargo and mail throughput at airports in this region is 4.7 times that of western China. Simultaneously, abundant moisture flux in monsoon regions\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e and localized circulation adjustments induced by urban heat island effects\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e jointly establish the thermodynamic-dynamic conditions for icing occurrence.\u003c/p\u003e \u003cp\u003eThe northern regions experienced significantly fewer icing events, with the three northeastern provinces recording a cumulative total of only 113 instances (accounting for \u0026lt;\u0026thinsp;3% of the national total). This is closely related to winter low temperatures inhibiting the formation of supercooled water and lower aviation traffic. However, it should be noted that winter frontal activities can still cause sudden icing risks. Although the annual average frequency in northwestern regions (such as Xinjiang and Gansu) remains relatively low, moderate-to-severe events account for 94.3\u0026ndash;97.9% of occurrences, indicating that their icing processes exhibit more sudden and high-intensity characteristics.\u003c/p\u003e \u003cp\u003eModerate-to-severe icing events (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) account for 97.7% of the total, highlighting the high-risk nature of icing hazards in China. The Sichuan Basin, with a cumulative total of 902 events, tops the list, validating the amplifying effect of topographic forcing on icing intensity\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Although the eastern coastal regions exhibit higher frequency, there are significant intensity variations: Guangdong and Shanghai report 100% and 99.6% moderate-to-severe events, respectively, while Zhejiang stands at 90.6%, reflecting regional heterogeneity in meteorological responses. Notably, nine provinces, including Hubei and Fujian, have an annual average of only 4 events, yet 100% of these are moderate-to-severe, indicating that icing risks in low-frequency areas exhibit a 'low-frequency but high-impact' characteristic.\u003c/p\u003e \u003cp\u003eIn summary, the spatial heterogeneity of icing in China is governed by three mechanisms: (1) aviation activity intensity, with flight density in economic core zones showing a significant positive correlation with icing frequency\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e; (2) terrain-climate synergy, where southwestern mountainous areas sustain persistent icing environments through dynamic uplift and moisture convergence, while the eastern monsoon region relies on abrupt moisture flux changes to trigger events; (3) human activity interference, as urban heat islands and industrial emissions alter local atmospheric stratification, increasing icing probability\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. This distribution pattern holds critical implications for air route planning and meteorological warnings, requiring differentiated strategies that prioritize routine risks in high-frequency zones and sudden threats in low-frequency areas.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Vertical Heterogeneity Characteristics and Multi-Mechanism Coupling Effects of Aircraft Icing Events in China\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe vertical distribution of icing events in China from 2011 to 2023 exhibits significant stratification dependence (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Statistics reveal that icing events are concentrated at altitudes of 2\u0026ndash;8 km, accounting for 89.6% of the total. Among these, the 3.5\u0026ndash;4 km altitude layer accumulated 787 instances (peak zone), followed by 5\u0026ndash;5.5 km and 6\u0026ndash;6.5 km layers with 739 and 673 instances, respectively. Notably, moderate-to-severe icing events accounted for 66.8% (526 instances) in the 3.5\u0026ndash;4 km layer, with risk severity displaying a bimodal vertical pattern: aside from the primary peak, the 7.5\u0026ndash;8.5 km layer accumulated 587 instances, representing 22.4% of severe cases. This phenomenon is closely tied to thermodynamic-dynamic conditions at different altitudes: moisture convergence and temperature gradients jointly sustain supercooled water enrichment at mid-to-low levels (2\u0026ndash;6 km)\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, while jet stream dynamic uplift at higher altitudes (\u0026gt;\u0026thinsp;7.5 km) triggers supercooled water generation at deep convective cloud tops.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003eFurther analysis of regional differences (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) reveals that the vertical distribution of icing events across provinces is significantly modulated by geographical climate and circulation systems: In the Sichuan Basin, 280 icing events (30.9% of the province\u0026rsquo;s total) occurred at 2\u0026ndash;4 km altitude, attributed to the basin\u0026rsquo;s terrain trapping low-level moisture\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. The specific humidity at 2\u0026ndash;4 km remains above 5 g/kg year-round\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e, combined with adiabatic cooling from topographic uplift, creating a persistent supercooled water environment. In Guangdong and the South China Sea region, 112 events (42.4% of the province\u0026rsquo;s total) were concentrated at 8\u0026ndash;10 km, distinct from inland provinces. This unique high-altitude icing mechanism arises from the synergy between deep convective cloud top expansion driven by tropical weather systems, dynamic uplift from subtropical jet streams\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e, and high-altitude moisture transport under maritime climate conditions. In the North China Plain, the 4\u0026ndash;6 km layer is the primary icing zone (e.g., Beijing with 27 events), where mid-level cloud system development during winter cold front passages and ice-nucleating effects from industrial aerosols\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e jointly enhance supercooled water generation. Though the 8\u0026ndash;10 km layer accounts for a high proportion of events in the southwestern plateau (e.g., 85% in Tibet), total occurrences are less than 10% of those in humid regions, reflecting the fundamental constraint of scant moisture on icing over the plateau\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e.\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe vertical heterogeneity of icing highlights the prominence of dual risk layers at mid-to-low altitudes (2\u0026ndash;4 km and 5\u0026ndash;6 km), which collectively account for 71.3% of national icing events. The former is dominated by topographic forcing and moisture convergence, while the latter is linked to frontal system uplift and urban aerosol effects\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Additionally, high-altitude sudden-risk zones (7.5\u0026ndash;9.5 km) are primarily distributed in eastern coastal areas like Guangdong and Shanghai, associated with tropical cyclone anvils and sudden supercooled water enrichment in jet stream zones\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Although such events represent only 18.5% of cases, their safety threat is heightened due to the difficulty of real-time avoidance during cruising phases. From an aviation meteorological management perspective, these vertical characteristics hold critical guidance for flight-phase risk mitigation: During climb/approach phases (\u0026lt;\u0026thinsp;4 km), focus on strong terrain-meteorological coupling risks in the Sichuan Basin and eastern urban clusters. During cruising phases (\u0026gt;\u0026thinsp;8 km), enhance icing monitoring and warnings in high-altitude jet stream zones over the South China Sea and eastern coast. Regionally, the North China Plain should prioritize monitoring mid-altitude frontal cloud systems in winter, while the southwestern plateau requires vigilance against sudden high-altitude icing under moisture-scarce conditions. The findings not only elucidate the physical mechanisms of vertical icing distribution but also provide a scientific basis for developing differentiated early-warning strategies.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Temporal Evolution Characteristics and Climate Response of Aircraft Icing Events in China\u003c/h2\u003e \u003cp\u003eThe temporal evolution of aircraft icing events in Chinese airspace from 2011 to 2023 exhibits multi-scale coupled characteristics (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). In terms of icing intensity distribution, moderate and above events (Moderate+) accounted for 77.6% of total records, with Moderate, Moderate-Severe, and Severe categories contributing 47.2%, 6.5%, and 23.9%, respectively, underscoring the high-risk nature of icing events in Chinese airspace\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. These events have been directly linked to multiple major aviation incidents in recent years\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e, making their temporal heterogeneity critical for in-depth analysis. On an interannual scale, the altitude of icing events shows a significant upward trend: before 2017, primary occurrence layers concentrated in 2000\u0026ndash;4000 m (peak at 3000\u0026ndash;4000 m, 150 annual average events), while post-2018 saw a rise at 500 m a\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). This phenomenon correlates closely with the rising atmospheric freezing level under climate warming\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e and enhanced vertical moisture transport driven by frequent extreme weather\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. As shown in Supplementary Fig.\u0026nbsp;1, temperatures in East Asia\u0026rsquo;s 2\u0026ndash;6 km layer increased by 0.8\u0026ndash;1.2\u0026deg;C and specific humidity rose by 10\u0026ndash;15% during 2011\u0026ndash;2023, directly promoting the expansion of high-altitude supercooled water generation conditions.\u003c/p\u003e \u003cp\u003eOn seasonal scales, icing events exhibit extreme temporal concentration. Winter (DJF) monthly averages reached 847 events, 7.3 times higher than summer (JJA, 116.6 events/month), with December, January, and February accumulating 818, 950, and 774 events, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Vertically, winter icing primarily occurred in 2000\u0026ndash;4000 m (68% of cases), but 21% of events were observed at 4000\u0026ndash;6500 m, reflecting seasonal synergy between frontal systems and high-altitude jet streams\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. Notably, icing altitudes follow an inverted-V annual pattern: the main occurrence layer rises from 3000 m in January to 4500 m by April, then retreats below 2500 m from July to September (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed), aligning with seasonal adjustments in East Asian monsoon thermal-moisture vertical profiles\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. At hourly resolution, icing frequency strongly couples with flight scheduling\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e and diurnal temperature-humidity cycles\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e: events remain below 100/h from 01:00\u0026ndash;06:00, surge post-06:00, peak at 10:00 (\u0026gt;\u0026thinsp;400/h), and sustain high levels through the afternoon (12:00\u0026ndash;18:00) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). However, the proportion of moderate-to-severe events decreases by 15% -20% during 09:00\u0026ndash;21:00, potentially due to daytime turbulence accelerating supercooled droplet collision-freezing\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e or temperature rises inhibiting sustained icing\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e.\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eIn summary, the temporal heterogeneity of icing events in China results from the synergistic interplay between natural climate change and human activities. Climate warming reshapes the vertical distribution of icing by elevating freezing level altitudes, while the increasing frequency of extreme weather intensifies seasonal and diurnal variability. Concurrently, increasing aviation traffic (e.g., during peak daytime hours) amplifies the temporal clustering of icing risks. These findings underscore that future aviation meteorological warnings must prioritize: (1) core mid-to-low altitude icing zones in winter, (2) climate-warming-driven expansion of high-altitude risk belts, and (3) sudden events during daytime flight-intensive periods. This framework provides theoretical support for dynamic risk management strategies.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Meteorological Driving Mechanisms and Regional Heterogeneity of Aircraft Icing Events in China\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe occurrence of aircraft icing events in China exhibits significant regional heterogeneity in meteorological conditions, driven by the synergy of atmospheric circulation patterns, vertical thermal-moisture distributions, and cloud microphysical processes (Supplementary Fig.\u0026nbsp;2). Under macro-circulation regimes, winter\u0026rsquo;s 'two-trough-one-ridge' structure in the 500 hPa geopotential height field governs frontal-type icing formation in North China: the Northeast Cold Vortex interacts with troughs extending southward to the North China Plain, where mid-upper-level north westerlies transport cold air, low-level shear lines trigger moisture convergence, and surface cold fronts generate deep cloud systems\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. Persistent cold advection from north westerlies at 700 hPa and 850 hPa, combined with enhanced near-surface moisture convergence via 1000 hPa shear flows (Supplementary Fig.\u0026nbsp;2d), jointly establish thermodynamic-dynamic conditions for frontal icing. In Beijing, icing events peak at 8\u0026ndash;10 km altitude (annual average of 100 events), with moderate-to-severe cases comprising 25\u0026ndash;30% in the 6\u0026ndash;10 km layer (Supplementary Fig.\u0026nbsp;3). This altitude range maintains stable temperatures of -12\u0026deg;C to -2\u0026deg;C (corresponding to 720\u0026ndash;555 hPa) and relative humidity of 45.8\u0026ndash;55.8% (Fig.S4). Industrial aerosols in North China (e.g., black carbon and sulfate) enhance ice-nucleating particle (INP) concentrations at 4\u0026ndash;6 km altitudes, potentially elevating supercooled water occurrence. Wu et al. demonstrated that assimilating real-time aerosol data improves supercooled water prediction accuracy by 22\u0026ndash;40% in this region\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. Although quantitative correlations between INPs and icing frequency require further observation-model integration, the persistent co-occurrence of high aerosol loading and moderate-to-severe icing events (Fig. S3) suggests aerosol microphysical effects likely amplify icing risks.\u003c/p\u003e \u003cp\u003eThe icing mechanisms in the Sichuan Basin are governed by dual influences of topographic locking and modulation by the southern branch trough (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). At 500 hPa, the southern branch trough of the westerlies drives warm, moist southwestern airflow into the basin, where it converges with post-trough cold air, creating a stratified instability with cold upper and warm lower layers. At 700 hPa, the Tibetan High synergizes with convergent basin wind fields to trigger warm-moist air uplift. Within the 2\u0026ndash;4 km layer, specific humidity reaches 5 g/kg, and cloud liquid water content attains 0.4\u0026ndash;0.5 g/kg (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec-d). Coupled with low temperatures (-3\u0026deg;C to -8\u0026deg;C), these conditions drive mixed-phase ice formation exceeding 60%, yielding an annual average of 39 icing events (75.7% of the total). This underscores the pivotal role of topographic dynamics in moisture retention \u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. Notably, while events at 8\u0026ndash;10 km altitudes are less frequent, moderate-to-severe cases constitute 30%, emphasizing the need to concurrently address sudden high-altitude risks.\u003c/p\u003e \u003cp\u003eThe icing mechanisms in eastern coastal regions reflect the interaction between subtropical jet streams and maritime climate (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). At 500 hPa, the westerly jet (16 m/s) and pre-trough southwestern airflow jointly transport warm-moist air. At 700 hPa, enhanced southwesterlies boost moisture flux, while 850 hPa shear lines trigger low-level convergence. In the Yangtze River Delta region, temperatures at 5\u0026ndash;7 km range from \u0026minus;\u0026thinsp;6\u0026deg;C to -12\u0026deg;C with cloud water content of 0.1\u0026ndash;0.2 g/kg, where the subtropical jet prolongs supercooled droplet persistence\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. Climate warming has driven an annual average rise of 120 m in the 0\u0026deg;C isotherm, shifting icing risks toward 5\u0026ndash;7 km. In Guangdong, high-altitude (8\u0026ndash;10 km) temperatures range from \u0026minus;\u0026thinsp;15\u0026deg;C to -25\u0026deg;C, but the South China Sea monsoon induces localized moisture enrichment (0.05\u0026ndash;0.1 g/kg) at convective cloud tops. Coupled with strong updrafts suppressing ice nucleation, this results in an annual average of 112 icing events\u0026mdash;a mechanism distinct from inland regions.\u003c/p\u003e \u003cp\u003eFrom the cloud microphysical perspective (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, S4), the supercooled droplet formation altitudes (3\u0026ndash;6 km) align vertically with the core icing event layers. Beijing's 4\u0026ndash;6 km layer exhibits cloud water content of 0.2\u0026ndash;0.3 g/kg, where low-temperature conditions (-5 to -10\u0026deg;C) promote glaze ice formation. In the Sichuan Basin, synergistic effects between high humidity (\u0026gt;\u0026thinsp;80%) at 2\u0026ndash;4 km and orographic uplift enhance droplet collision efficiency. Although the 5\u0026ndash;7 km layer over eastern coastal regions shows lower cloud water content, jet stream-driven dynamical uplift delays supercooled water freezing. This vertical configuration divergence reveals that orographic dynamics dominate moisture enrichment for inland icing, while maritime climates coupled with jet stream modulation shape elevated risks in coastal zones.\u003c/p\u003e \u003cp\u003eThese differentiated characteristics provide explicit guidance for aviation meteorological warnings: North China requires focused attention on mid-level frontal cloud systems during cold front passages, Sichuan Basin should prioritize enhanced low-altitude monitoring in topographically enclosed areas, Eastern coastal regions need to establish high-altitude warning thresholds tailored for jet stream zones. Under climate warming, the vertical migration trends of icing risk layers (e.g., increasing frequency at high altitudes in Guangdong) must be integrated into dynamic risk assessment frameworks.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eAircraft icing events in China exhibit pronounced spatial gradients, with high-incidence zones concentrated in the southwestern region (annual average of 69.7 events) and eastern coastal areas (19% of total incidents), jointly driven by orographic dynamics and aviation activity intensity. Although the northwestern region experiences lower frequencies, over 94% of its events reach moderate-to-severe intensity, demonstrating a \"low-frequency, high-impact\" risk profile. Vertically, icing events predominantly occur between 2\u0026ndash;8 km altitude: low-to-mid levels (2\u0026ndash;6 km) are governed by moisture convergence, while upper layers (\u0026gt;\u0026thinsp;7.5 km) rely on jet stream-induced dynamical uplift, revealing synergistic regulation by terrain and atmospheric circulation. Temporally, winter (DJF) icing frequency surpasses summer by 7.3 times, with the primary icing layer ascending at 500 m/year since 2018, closely linked to rising atmospheric freezing levels and intensified moisture transport under climate warming.\u003c/p\u003e \u003cp\u003eRegionally, North China\u0026rsquo;s frontal icing is driven by the \"two-trough-one-ridge\" circulation pattern and cold front intrusions, exacerbated by mid-altitude cloud development and industrial aerosol ice nucleation effects. The Sichuan Basin experiences persistent warm-moisture advection via the southern branch trough and topographic confinement, where low-altitude high humidity (specific humidity\u0026thinsp;\u0026gt;\u0026thinsp;5 g/kg) elevates mixed-phase ice prevalence (\u0026gt;\u0026thinsp;60%). Coastal regions exhibit distinct high-altitude supercooled water enrichment mechanisms regulated by subtropical jet streams and the South China Sea monsoon. Cloud microphysical analyses confirm vertical alignment between supercooled droplet formation heights (3\u0026ndash;6 km) and icing core layers, with inland terrain-forced moisture configurations contrasting sharply with marine-influenced coastal vertical distributions.\u003c/p\u003e \u003cp\u003eProposed region-specific warning strategies include: monitoring mid-altitude frontal cloud systems in North China, enhancing low-altitude surveillance in Sichuan, and establishing high-altitude jet stream thresholds for coastal areas. Climate warming necessitates dynamic assessment of icing layer vertical migration trends (e.g., increasing high-altitude events in Guangdong). Study limitations involve subjectivity in Pilot Reports (PIREPs) and insufficient precision in local meteorological simulations. Future efforts should integrate multi-source observations (satellite retrievals, airborne sensors) with high-resolution numerical models to develop a multi-scale prediction framework for aircraft icing across China.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe ERA5 reanalysis data were downloaded from https://www.ecmwf.int/en/forecasts/dataset/ecmwf-reanalysis-v5.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by National Key Research and Development Program of China (No. 2022YFC3002502), National Natural Science Foundation of China (NSFC) Excellent Young Scientists Fund (No. 42422506), the National Natural Science Foundation of China (No. 42275122), and the National Key Scientific and Technological Infrastructure project \u0026ldquo;Earth System Science Numerical Simulator Facility\u0026rdquo; (EarthLab). Ting Yang would like to express gratitude towards the Program of the Youth Innovation Promotion Association (CAS).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAuthors and Affiliations\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003csup\u003e1.\u003c/sup\u003e\u003c/strong\u003e\u003cstrong\u003eNanjing University of Aeronautics and Astronautics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWei Zhang, Minhua Hu,\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003csup\u003e2.\u003c/sup\u003e\u003c/strong\u003e\u003cstrong\u003eState Key Laboratory of Atmospheric Environment and Extreme Meteorology, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTing Yang, Yining Tan, Shiyu Zhang, Liang Li, Yutong Tian,\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003csup\u003e3.\u003c/sup\u003e\u003c/strong\u003e\u003cstrong\u003eAviation Meteorological Center of the Air Traffic Management Bureau, Civil Aviation Administration of China, Beijing, China\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWei Zhang, Tong Lv, Chongyu Zhang, Hongtai Zhang, Sisi Gao\u003c/p\u003e\n\u003cp\u003eContributions\u003c/p\u003e\n\u003cp\u003eConceptualization: Ting Yang, Wei Zhang. Formal analysis: Yining Tan, Shiyu Zhang, Liang Li, Yutong Tian. Funding acquisition: Ting Yang. Investigation: Minhua Hu Methodology: Wei Zhang. Project administration: Ting Yang. Resources: Wei Zhang. Software: Yining Tan, Shiyu Zhang, Liang Li, Yutong Tian. Supervision: Ting Yang, Wei Zhang, Minhua Hu. Validation: Tong Lv, Chongyu Zhang, Hongtai Zhang, Sisi Gao, Yining Tan. Visualization: Yining Tan, Shiyu Zhang, Liang Li, Yutong Tian, Writing, original draft: Ting Yang, Yining Tan, Shiyu Zhang, Liang Li, Yutong Tian. Writing, reviewing and editing: Ting Yang, Wei Zhang.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCorresponding authors\u003c/p\u003e\n\u003cp\u003eCorrespondence to Ting Yang ([email protected])\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCompeting interests\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eFrohboese, P. and Anders, A. 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Evolution of cloud droplet temperature and lifetime in spatiotemporally varying subsaturated environments with implications for ice nucleation at cloud edges. \u003cem\u003eAtmospheric Chemistry and Physics\u003c/em\u003e, 24, 11653\u0026ndash;11672 (2024).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6902239/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6902239/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAircraft icing critically threatens aviation safety globally. This study leverages China's first public 13-year (2011\u0026ndash;2023) pilot reports (PIREPs) and multi-source data to elucidate the spatiotemporal dynamics and climatic drivers of icing across China. Key findings reveal: (1) a distinct southwest-high, east-moderate, northwest-low spatial pattern driven by topography, aviation density, and regional climate; (2) vertical stratification with peak occurrence at 2\u0026ndash;8 km, governed by moisture-temperature coupling at mid-low altitudes (2\u0026ndash;6 km) and jet stream uplift at higher levels (\u0026gt;\u0026thinsp;7.5 km); (3) winter frequency surpasses summer by 7.3 times, with a significant post-2018 ascent of the primary icing layer at ~\u0026thinsp;500 m a\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, strongly linked to rising freezing levels under global warming; (4) divergent regional mechanisms - frontal systems and aerosols in North China, terrain-trapped moisture in the Sichuan Basin, and ocean-jet stream interactions along coasts. These insights underpin region-specific warning strategies (targeting mid-altitude fronts, low-altitude terrain zones, and upper-level jets) and advance climate-resilient aviation meteorology through improved risk management.\u003c/p\u003e","manuscriptTitle":"Multiscale Dynamics and Climatic Drivers of Aircraft Icing in China: Insights from 13 Years of Pilot Reports (2011-2023)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-25 11:05:02","doi":"10.21203/rs.3.rs-6902239/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4ee91012-291e-495a-bfcd-5dbebace1259","owner":[],"postedDate":"June 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":50458067,"name":"Earth and environmental sciences/Climate sciences"},{"id":50458068,"name":"Earth and environmental sciences/Environmental sciences"}],"tags":[],"updatedAt":"2025-09-04T05:08:13+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-25 11:05:02","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6902239","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6902239","identity":"rs-6902239","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}