Abstract. Evolution mechanisms of explosive advection sea fog coupled with long-range dust transport over East Asia remain unclear. This study investigates a dust-advection sea fog event using multi-source data. Results show that dust underwent significant aging during transport, promoting sea fog under high humidity (RH > 90 %). Before sea fog formation (Stage 3: 12:40–16:47 on the 25th) and during the sea fog period (Stage 4: 16:47–19:30 on the 25th), the proportion of 0–1 μm particles decreased by 18 % and 24 %, respectively. The proportion of 1–2.5 μm particles increased by 5 % and 4 %, respectively. The proportion of 2.5–10 μm particles increased by 13 % and 20 %, respectively. This indicates that aging enhanced dust hygroscopicity. Unlike classical advection cooling, radiative forcing of dust and cold air formed a deep inversion (9 °C) before fog, which with warm-moist advection suppressed turbulent mixing and provided a favourable thermodynamic background for fog maintenance. The threshold ranges of turbulence parameters (U, TKE, u⁎, Iu, Iv, Iw) were relatively distinct when sea fog maintains visibility within 1 km. The friction velocity (u⁎) was within a narrow range of 0.62–0.69 ms⁻¹, indicating high sensitivity to u⁎. The system showed a significant characteristic of turbulence acting first and fog responding later during the late stage of mist. The downward longwave radiation (DLR) was highly sensitive to changes in fog layer structure. Fog dissipation was caused by circulation adjustment and re-invasion of dry-cold dust carried by northerly winds, destroying phase equilibrium. These findings advance understanding of sea fog under complex aerosol backgrounds.

Snow formation is a complex interplay of multiple microphysical growth processes, and the prevailing snow characteristics are inherently linked to local climate. However, the persistent shortage of observations for characterizing snow microphysics at a global scale continues to constrain our understanding of snow growth processes. Here, we investigate snow riming and aggregation signatures in stratiform precipitation through triple-frequency radar observations collected during coordinated field campaigns across Southern China, the Eastern United States, Western Europe, Northern Europe and Antarctica. The results suggest that the velocity-based riming estimates are generally consistent with triple-frequency observations, and the riming frequency increases with temperature. Our analysis of dual-frequency observations in these field campaigns qualitatively indicate the dendritic growth zone around -15 degrees C playing a key role in initiating enhanced snow size growth, and reveals a generally temperature-dependent snowflake growth characteristics. The snow over Eastern US is characterized by the most prominent riming growth, corresponding to moderate to heavy riming. Triple-frequency signatures of snowflakes over west Europe are consistent with Southern China, while the latter shows a higher degree of riming. The weakest snow growth signatures were found over west Antarctica, potentially owing to the scarcity of ice nucleating particles and available water vapor for deposition. In addition, our statistics reveal a latitudinal dependence for snowfall detection limitations with current spaceborne Ku- and Ka-band radars, and shed novel insights into future triple-frequency satellite missions as well as joint application of weather and spaceborne radars.

This study focused on the impact of vertical wind shear (VWS) in the stratosphere on the asymmetry of stratospheric gravity waves (SGWs) generated by tropical cyclones (TCs), based on a set of numerical simulations of TC-SGWs completed under different stratospheric background wind conditions. Results showed that a constant background easterly wind leads to a slightly asymmetric distribution of TC-SGWs, with intense waves in the lower stratosphere located on the upwind side, attributable to the asymmetry in TC structure under the condition of the easterly wind. In contrast, VWS induces a notable asymmetric distribution of TC-SGWs through directional critical levels. Spectral and wavenumber-vector analyses revealed that the co-occurrence of radial and tangential propagation of TC-SGWs modifies the critical-level filtering effect, producing a final distribution with intense waves located mainly in the southeastern quadrant relative to a TC center and to a lesser extent in the northeastern and southwestern quadrants, rather than throughout the eastern quadrants as a whole.

The electrification process within thunderstorm clouds depends critically on the evolution of the background environmental dynamics and microphysical processes, yet characterization of the coupling among lightning and dynamics-microphysical processes has been limited by observational constraints. This study employs synchronized observations from Phased Array X-Band Dual-Polarization Radar and a Low-Frequency Lightning Location System and designs a region statistical method for filtering changes in physical quantities near lightning initiation regions. This method is applied to two independent lightning initiation episodes within a convective merger over Tunchang County, Hainan Province, on 14 September 2025. The results show that the lightning initiation regions exhibit a characteristics of peak-evolution in the spatial percentage of the phase state of low-density graupel particles. These regions also show a higher intensity and uneven distribution of environmental vertical updrafts, eddy dissipation rate and ice-water content. In addition, statistical correlations of environmental physical quantities near the lightning initiation area suggest that dynamics may serve as significant contributors to the onset of this thunderstorm lightning event in Hainan.

Abstract. Secondary ice production (SIP) substantially enhances ice concentrations in clouds, thereby modulating precipitation and climate, yet underlying SIP mechanisms over the Tibetan Plateau (TP) remain poorly understood. This study investigated the observational evidence and environmental dependence of SIP in convective clouds over the TP based on aircraft observations. The SIP ratio (measured ice to estimated INP concentrations) was introduced to quantify ice enhancement. Flight observations on 6 July 2014 revealed ice concentrations reached 205.4 L−1 in convective clouds, with the SIP ratio peaking at 1000 near −5 ℃. The SIP effective temperature window extended to −16 ℃, substantially broader than the classical Hallett–Mossop (HM) range. Between −3 ℃ and −8 ℃, the HM process played the dominant role, accompanied by ice-ice collisional breakup (BR) and freezing droplet shattering (DS). Between −8 ℃ and −16 ℃, SIP persisted despite reduced HM efficiency, sustained by DS and BR, plus possible upward transport of supercooled large droplets and columnar crystals from warmer levels. SIP-active legs exhibited bimodal ice particle spectra with peaks below 100 μm and between 200 and 300 μm. The size of supercooled droplets dictated SIP initiation, with thresholds of approximately 24 μm above −8 ℃ and 200 μm below −8 ℃. Seven flights further indicate that temperature determined SIP occurrence and dominant mechanism, and hydrometeor concentration exhibited a pronounced positive correlation with the SIP ratio. These findings provide new insights into SIP processes in high‑altitude convective clouds and important implications for improving cloud microphysical parameterizations in weather and climate models.

Abstract Using the multi‐frequency radar suite, ground‐based observations, and the Weather Research and Forecasting (WRF) model with the Predicted Particle Properties microphysics scheme with the version of two‐ice category (P3‐2ice), we study the characteristics of a cold‐air outbreak (CAO) snowfall event on 6–7 December 2024. The cloud system is shallow convection, with the microphysical characteristics differing between the first and second snowfall periods. The WRF model reproduces the synoptic‐scale weather system and mesoscale structure well, but underestimates the event‐averaged snow rate and rime mass fraction by approximately 52% and 24%, respectively. Within the riming process, the collection of cloud water by ice is the dominant pathway. However, the fixed collection efficiency decouples riming from wind shear. To study the impact of collection efficiency on snow rate, we increase the efficiency as a simplified approach to represent the potential effect of shear‐generated turbulence on riming. The results of sensitivity experiments reveal that the snow rate exhibits a positive correlation with collection efficiency, but with contrasting behaviors between the two snowfall periods. In the first period, persistent severe underestimation occurs; in the second period, overestimation occurs when efficiency is high, and the rime mass fraction shows a nonlinear response to efficiency. These results indicate that a fixed collection efficiency is inadequate and a dynamic environment‐constrained efficiency is required. The research provides new insights into how to improve the riming process parameterization, contributing to a better understanding of the dynamic and microphysical characteristics of CAO snowfall.

This study introduces a tornado perturbation model utilizing the cyclostrophic wind model, implemented through a shallow-water equation framework. Four numerical experiments were conducted: a single cyclonic wind perturbation (EXP1), a single low-geopotential height perturbation (EXP2), a cyclonic wind perturbation with a 0 Coriolis parameter (EXP3), and a single anticyclonic wind perturbation (EXP4). The outputs showed that in a static atmosphere setting, a small-scale cyclonic wind perturbation generated a tornado-like pressure structure. The centrifugal force in the central area exceeded the pressure gradient force, causing air particles to flow outward, leading to a pressure drop and strong pressure gradient. The effect of the Coriolis force is negligible for meso-γ-scale and smaller systems, while for meso-β-scale and larger systems, it begins to have a significant impact. The results indicate that a robust cyclonic and an anticyclonic wind field can potentially generate a pair of cyclonic and anticyclonic tornadoes when the horizontal vortex tubes in an atmosphere with strong vertical wind shear tilt, forming a pair of positive and negative vorticities. These tornadoes are similar but have different rotation directions.

To validate the Pangu model’s forecasting capability for the rapid intensification (RI) process of tropical cyclones (TCs), forecasts of different RI/non-RI TCs were produced both by the Weather Research and Forecasting (WRF) model and the Pangu model. The results of comparative analyses indicate that the Pangu model generally forecasts weaker TC intensity, and is not capable of predicting the trend of RI. Correspondingly, Pangu’s RI TC track forecasts are also less accurate. It was also found that the RI process has a larger impact on Pangu’s track forecasting capability than WRF’s. This work demonstrates Pangu’s weakness in RI prediction and discusses the possible mechanisms involved. Future research may focus on physically constrained AI TC forecasting models, which could be a solution to the forecasting of extremely severe weather systems such as rapidly intensifying TCs.摘要本研究针对当前人工智能气象模型在极端天气预报中的适用性这一热点话题, 评估盘古模型对热带气旋快速增强过程的预报能力. 通过将盘古模型与传统的WRF模型对多个快速增强/非快速增强个例的预报结果进行对比分析, 发现: 盘古模型存在系统性强度预报偏弱的问题, 无法有效捕捉快速增强台风的非线性增长趋势; 相应地, 其对于经历快速增强过程热带气旋的路径预报误差也显著大于WRF模型, 表明快速增强过程对盘古模型路径预报能力的负面影响更为突出. 研究揭示了人工智能模型在预报极天气时的固有局限, 并为未来发展物理约束的人工智能模型提供了方向.

The stratospheric gravity waves generated by tropical cyclones (TC-SGWs) are useful for the monitoring of tropical cyclones (TCs) and are also important for the gravity-wave parameterization in numerical models, as they represent a distinct type of gravity waves. Previous studies on TC-SGWs have not characterized TC-SGW global distribution and corresponding local structure related to the background wind. Here we show the global distribution of the TC-SGWs based on 21 years of Atmospheric Infrared Sounder observations, and reveal three global hotspots of the waves as the North Atlantic-Northeast Pacific, the Northwest Pacific, and the South Pacific-Southern Indian region. We also characterize the local structure of the three hotspots and find that although displaying diverse anisotropic structures, they are all shaped by the combination of filtering and refraction effects of the background wind. Our findings provide a guide for global TC-SGW hotspots and demonstrate the contributions of the background wind, which can further provide a preliminary guide for TC monitoring through satellite observations of TC-SGWs.

This paper investigates the impact of the model top and damping layer on the numerical simulation of tropical cyclones (TCs) and reveals the significant role of stratospheric gravity waves (SGWs). TCs can generate SGWs, which propagate upward and outward into the stratosphere. These SGWs can reach the damping layer, which is a consequence of the numerical scheme employed, where they can affect the tangential circulation through the dragging and forcing processes. In models with a higher top boundary, this tangential circulation develops far from the TC and has minimal direct impact on TC intensity. By comparison, in models with a lower top (e.g., 20 km), the damping layer is located just above the top of the TC. The SGW dragging in the damping layer and the consequent tangential force can thus induce ascent outside the eyewall, promote latent heat release, tilt the eyewall, and enlarge the inner-core radius. This process will reduce inner-core vorticity advection within the boundary layer, and eventually inhibits the intensification of the TC. This suggests that when the thickness of the damping layer is 5 km, the TC numerical model top height should be at least higher than 20 km to generate more accurate simulations.

Cement production consumes large amounts of depleted resources and energy, and causes environmental pollution. In order to reduce cement consumption and realize the closed-loop recycling of solid waste, cold bonded solid waste wrap-shell lightweight aggregates (SWSLAs) with a sextuplet blended system composed of dredged sediments, mineral powder, steel slag, phosphogypsum, fly ash, and a minimal amount of cement were prepared. Through the single-factor experiment, the influences of the types and dosages of solid wastes in the nuclear phase of SWSLAs (SWSLAs-NP) and shell phase of SWSLAs (SWSLAs-SP) on the strength and water resistance were explored, and the optimum ratio was obtained. On this basis, the influence of the types and amounts of activators incorporated in SWSLAs on the physical properties of aggregates was studied, and the primary microstructure of the aggregate was characterized. Our results showed that the optimal ratio of solid waste in the SWSLAs-NP was: 40 wt% of dredged sediments, 24 wt% of mineral powder, 18 wt% of steel slag, and 18 wt% of phosphogypsum. The optimal weight ratio of cement and solid waste in the SWSLAs-SP was 5:95. The resulting aggregate had a bearing capacity of single grain of 73.83 N and a water-resistance coefficient of 0.67. After the above aggregates were treated with Na2SO4 (activator) at 2%, the bearing capacity and water-resistance coefficient of the aggregates increased by 47.00% and 11.94%, respectively. The performances were even better than that of the aggregate composed of100w cement in the shell phase. Microstructural observations demonstrated that the structure of the raw material was reconstructed under the action of Na2SO4, and the raw materials reacted with each other, and thus the densification of the aggregate and its core-shell interface structure was enhanced, which improved the comprehensive performance of the aggregate. This study represents a step toward efficient utilization of industrial solid wastes.

A climatology of stratospheric gravity waves (SGWs) induced by tropical cyclones (TC-SGWs) is necessary for stratospheric aviation safety and accurate numerical weather prediction. Few previous works have characterized the climatology of TC-SGWs, and the relative importance of the source and background wind for TC-SGWs has not been clearly established. Here we present the distribution of TC-SGWs formed over the northwest Pacific Ocean based on 30 years of ERA5 reanalysis data. Using explainable artificial intelligence, we found the background wind in the lower stratosphere to be more important than TCs in controlling the distribution pattern of TC-SGWs. The background wind shear can influence the direction of TC-SGW propagation by refraction and filtering, which influences the distribution pattern of the TC-SGWs. The TC intensity only influences the TC-SGW intensity. Our results provide information on TC-SGW hotspots and suggest the importance of the background wind shear.

To investigate the relationship between microphysical and chemical characteristics of size-resolved fog droplets in different regional backgrounds, we conducted observational experiments in urban, mountainous, rainforest, and rural areas of China. Fog water samples across different diameter ranges (4-16 mu m, 16-22 mu m, and >22 mu m) were collected, alongside fog droplet spectra data. Our findings reveal a close relationship between pH value, electrical conductivity (EC), total ion concentration (TIC) of droplets, and droplet sizes, with smaller droplets exhibiting stronger acidity and higher ion concentrations. Significant differences in chemical composition are observed across size ranges and regional backgrounds. Droplet number concentration (N) and liquid water content (LWC) distributions in different regional backgrounds are skewed, with peak diameters of LWC spectra similar to those of N spectra, yet overall spectral distributions varied significantly. Droplet number concentrations are highest in urban area, while large droplets contribute more to overall LWC in mountainous, rainforest, and rural areas. No direct evidence linked LWC or surface area (S) to LWC ratio to water-soluble ion concentrations of size-resolved fog droplets in different regional backgrounds. However, by adjusting the contributions of S and LWC proportions of different-sized droplets to the ion concentration proportions, we find that expanding the LWC proportion to 2.43 times and decreasing the S proportion to 0.2 times for large droplets, while decreasing the LWC ratio to 0.76 times for small droplets, provided a better explanation for the distribution of ion concentrations. This study advances our understanding of the intricate relationship between the micro physical and chemical characteristics of fog, helping to develop more robust and comprehensive models for fog prediction and management.

The microphysical and dynamic evolution characteristics of two convections (labeled A and B) were analyzed using polarimetric radars during the same weather conditions under the influence of ground-based rockets and artilleries containing silver iodide (AgI). The ice and liquid water content (IWC and LWC, respectively), hydrometeor classification and three-dimensional wind structure were retrieved to analyze the convection evolution. The results indicate that the convective evolution trends after AgI seeding are related to the preoperation dynamic and microphysical structure. The ice processes of convection A are more active before operation, with a high echo center of gravity, larger IWC and LWC, and a predominance of graupel above the freezing level. The center of gravity of the convection gradually decreases, and the cloud collapses and gradually dissipates during AgI seeding. Convection B has more active liquid processes, with a stronger updraft but lower IWC and LWC. During AgI seeding, ice processes of the convection have a tendency to be enhanced, with a higher echo center of gravity and increases in IWC, and LWC below the freezing level. During significant wind shear, the path of convection may tend to align with the background guided flow at different levels, depending on the different intensities of convection influenced by AgI seeding. The convection intensity and its matching with vertical wind shear should be considered when artificially seeding convection.

The microphysical characteristics of precipitation and their differences among four typical weather systems over Hainan Island were investigated via multi-source observations from 2019 to 2023. We find that the cold fronts (CFs) have the greatest concentration of small raindrops, with a more substantial raindrop condensation process. The subtropical highs (SHs), with primarily deep convection and more prominent evaporation at low levels, lead to greater medium-to-large raindrops (diameters > 1 mm). Tropical cyclones (TCs) are characterized mainly by raindrop condensation and breakup, resulting in high concentrations of small raindrops and low concentrations of large raindrops. The trough of low pressures (TLPs) produces the lowest concentration of small raindrops because of evaporation processes. The convective clusters of the SHs are between maritime-like and continental-like convective clusters, and those of the other three types of weather systems are closer to maritime-like convective clusters. The relationships between the shape parameter (μ) and the slope parameter (Λ), as well as between the reflectivity factors (Z) and the rain rates (R), were established for the four weather systems. These results could improve the accuracy of radar quantitative precipitation estimation and the microphysical parameterizations of numerical models for Hainan Island.

In August 2022, Pakistan experienced an unprecedented precipitation event that caused significant damage. Analysis of the observations reveals that this extreme rainfall is primarily driven by anomalous atmospheric zonal advection, resulting in an anomalous water vapor concentration in Pakistan. The climatological meridional advection also contributes to this flooding. Anomalous easterly winds and low-level vertical convection combine to be critical factors contributing to the moisture concentration over the country. Further investigation identifies the air-sea interaction over the tropical Indian Ocean and abnormal warming over the Arabian Sea are crucial factors influencing this extreme flooding event. The concurrent occurrence of a negative Indian Ocean Dipole event and the warming sea surface temperature anomalies in the northern Arabian Sea intensifies the easterly winds over Pakistan, helping to transfer the anomalous water vapor from the remote region into Pakistan, ultimately contributing to the extreme flooding in 2022.

Water-based aerosol is widely used as an effective strategy in electro-optical countermeasure on the battlefield used to the preponderance of high efficiency, low cost and eco-friendly. Unfortunately, the stability of the water-based aerosol is always unsatisfactory due to the rapid evaporation and sedimentation of the aerosol droplets. Great efforts have been devoted to improve the stability of water-based aerosol by using additives with different composition and proportion. However, the lack of the criterion and principle for screening the effective additives results in excessive experimental time consumption and cost. And the stabilization time of the aerosol is still only 30 min, which could not meet the requirements of the perdurable interference. Herein, to improve the stability of water-based aerosol and optimize the complex formulation efficiently, a theoretical calculation method based on thermodynamic entropy theory is proposed. All the factors that influence the shielding effect, including polyol, stabilizer, propellant, water and cosolvent, are considered within calculation. An ultra-stable water-based aerosol with long duration over 120 min is obtained with the optimal fogging agent composition, providing enough time for fighting the electro-optic weapon. Theoretical design guideline for choosing the additives with high phase transition temperature and low phase transition enthalpy is also proposed, which greatly improves the total entropy change and reduce the absolute entropy change of the aerosol cooling process, and gives rise to an enhanced stability of the water-based aerosol. The theoretical calculation methodology contributes to an abstemious time and space for sieving the water-based aerosol with desirable performance and stability, and provides the powerful guarantee to the homeland security.

Abstract The physical behavior of a falling raindrop is governed by delicate fluid dynamics and thermodynamics, and oscillates with time. Despite this time‐variant nature, past observational and simulation studies have aimed to generalize parameterizations for describing rain microphysics bearing the assumption that raindrops fall at terminal speeds with an equilibrium shape. However, the applicability of this hypothesis in a realistic atmosphere that is inherently turbulent remains an open question. Here, we employ novel retrieval techniques to quantify the impact of turbulence on raindrop microphysics using long‐term in situ observations with careful assessment of the wind effect. We find that raindrop microphysics increasingly deviate from the equilibrium state as the turbulence dissipation rate increases, and this effect is more pronounced for large raindrops. We present turbulence‐invoked rain microphysical parameterizations which shed light on the complex interactions between turbulence dynamics and raindrop microphysics.

Meteorological radars, as remote sensing instruments, play a vital role in observing clouds and precipitation. However, due to the complexity of hydrometeors in shape, density, diameter, orientation, and particle size distributions, accurate quantification of the inner microphysical characteristics of a cloud/precipitation system is challenging for a single-frequency radar. Recently, the advancement in scattering theory of hydrometeors, computer science, and hardware manufacturing (such as millimeter-wave devices) has stimulated the application of multi-frequency radars, bringing novel observations for an improved understanding of cloud and precipitation microphysics. Over the past few years, the multi-frequency vertical detection techniques have evolved from the new retrieval methods being enlightened by scattering theory to a new stage of the crucial microphysical processes being revealed by field observations. In this paper, from the perspectives of liquid and frozen hydrometeor microphysics, we introduce the key techniques used for dual- and triple-frequency radar retrieval techniques based on the scattering and attenuation of hydrometeors. Meanwhile, enlightened by the scattering of hydrometeors, we propose that the multi-frequency radar detecting techniques are developing from the classical W/Ka/X wavelengths to a "triple-frequency plus" stage, involving radars with shorter wavelengths and/or longer wavelengths. With spaceborne radars being developed from single-frequency to dual-frequency radars, the improvement of ground-based multi-frequency radars is expected to provide crucial support to future spaceborne multi-frequency radar missions.