Search Results (273)

Polar mesocyclones are often the cause of sudden worsening of weather conditions, including strong winds, snowfall with low visibility, and storms. The short lifetime, rapid development, high movement speeds, and small sizes, combined with a lack of meteorological observations over the Arctic seas, create difficulties in forecasting associated weather phenomena. High-resolution numerical modeling can help address this issue. The emergence and development of polar lows (PLs) significantly depend on the properties of the underlying surface, which largely determine the dynamic properties of the atmosphere in the boundary layer. This article is dedicated to assessing the sensitivity of the configuration ICON-Ru of the model ICON with a 2.0 km grid spacing to changes in the sea ice boundary and sea surface temperature (SST) when forecasting the formation and development of PLs. The results showed that the presence of artificial ice in the model almost completely suppresses the development of PLs in cases where the vortex does not have a strong connection with the jet stream. Heating the SST to 278.15 K while simultaneously shifting the ice boundary northward leads to increased thermal instability, rising sensible and latent heat fluxes, and higher CAPE, which enhances PLs, with the degree of enhancement depending on the nature of the vortex formation itself. Full article

Using station observations, the JRA-55 reanalysis dataset, and the CESM2 model, this study investigates the impacts of the stratospheric polar vortex (SPV) on winter near-surface wind speed (NSWS) over China across interannual and interdecadal timescales. On the interannual timescale, a strong SPV leads to a downward-extension signal that generates negative geopotential height anomalies over the Arctic, skewed toward the Atlantic sector. The associated surface response resembles the positive phase of the Arctic Oscillation (AO), resulting in reduced NSWS over northern China. In contrast, a weak SPV produces opposite effects. On the decadal timescale, a weakened SPV induces positive height anomalies over the Arctic that shift toward Northeast Eurasia. The surface response over the polar region stimulates a wave train, which drives a positive height anomaly over the North Pacific. The pressure gradient between East Asia and the North Pacific suppresses NSWS over eastern China. The response of China’s NSWS to interannual SPV variability is more pronounced than its response to interdecadal changes. CESM2 model simulations confirm these contrasting responses and the associated mechanisms. Full article

A vector vortex beam (VVB) combines the phase singularity of a vortex beam (VB) with the anisotropic polarization of a vector beam, enabling the transmission of complex optical information and offering broad application prospects in optical sensing, high-capacity communication, and high-resolution imaging. In this work, we present a detailed theoretical analysis of the generation and detection of VVBs with Laguerre–Gaussian (LG) and Bessel–Gaussian (BG) forms. Particular emphasis is placed on the polarization characteristics of VVBs, the evolution of beam profiles after passing through polarizers with different orientations, and the interference features arising from the coaxial superposition of a VVB with a circularly polarized divergent spherical wave. To validate the theoretical analysis, LGVVBs were experimentally generated using a Mach–Zehnder interferometer by superposing two vortex beams with opposite topological charges and orthogonal circular polarizations. Furthermore, the introduction of an axicon enabled the direct conversion of LGVVBs into BGVVBs. The excellent agreement between theoretical predictions and experimental observations lays a solid foundation for beginners to systematically understand VVB characteristics and advance future research. Full article

To design novel imaging devices, we use masks coded with numerical sequences. These masks work in conjunction with varifocal systems that implement zero-throw tunable magnification. Some masks control field depth, even when the size of the pupil aperture remains fixed. Pairs of vortex masks are used to implement tunable phase radial profiles, like axicons and lenses. The autocorrelation properties of the Barker sequences are applied to the generation of narrow passband windows on the OTF. For this application, we apply Barker matrices in rectangular coordinates. A similar procedure, but now in polar coordinates, is useful for sensing in-plane rotations. We implement geometrical transformations by using zero-throw, tunable, anamorphic magnifications. Full article

Multiple-Q magnetic states encompass a broad class of noncollinear and noncoplanar spin textures generated by the superposition of spin density waves. In this study, we theoretically explore the emergence of vortex crystals formed by multiple-Q spin density waves on a two-dimensional triangular lattice with $D_{3\mathrm{h}}$ point group symmetry. Using simulated annealing applied to an effective spin model, we demonstrate that the synergy among the easy-plane single-ion anisotropy, the biquadratic interaction, and the out-of-plane Dzyaloshinsky–Moriya interaction defined in momentum space can give rise to a variety of double-Q and triple-Q vortex crystals. We further examine the role of easy-plane single-ion anisotropy in triple-Q vortex crystals and show that weakening the anisotropy drives topological transitions into skyrmion crystals with skyrmion numbers $\pm 1$ and $\pm 2$. The influence of an external magnetic field is also analyzed, revealing a field-induced phase transition from vortex crystals to single-Q conical spirals. These findings highlight the crucial role of out-of-plane Dzyaloshinskii–Moriya interactions in stabilizing unconventional vortex crystals, which cannot be realized in systems with purely polar or chiral symmetries. Full article

Major stratospheric sudden warmings are key processes in the coupling between the stratosphere and the troposphere, exerting a direct influence on mid-latitude climate variability. This study evaluates projected changes in the frequency of these phenomena during the 2006–2100 period using six high-top general circulation models from the CMIP5 project under the Representative Concentration Pathway scenarios 2.6, 4.5, and 8.5. The analysis combines the full future period with a moving-window approach of 27 and 48 years, compared against both the satellite-era (1979–2005) and extended historical (1958–2005) periods. This methodology reveals that model responses are highly heterogeneous, with alternating periods of significant increases and decreases in event frequency, partially modulated by internal variability. The magnitude and statistical significance of the projected changes strongly depend on the chosen historical reference period, and most models tend to reproduce displacement-type polar vortex events preferentially over split-type events. These results indicate that assessments based solely on multi-model means or long aggregated periods may mask subperiods with robust signals, although some of these may arise by chance given the 5% significance threshold. This underscores the need for temporally resolved analyses to improve the understanding of stratospheric variability and its potential impact on climate predictability. Full article

Xinjiang is a critical wind energy region in China. This study characterizes extreme wind speed (EWS) events in Xinjiang by using ERA5 reanalysis (1979–2023) and station observations (2022–2023). Through k-means clustering and wind power density classification, four distinct regions and representative nodes were identified, aligned with the “Three Mountains and Two Basins” topography: Region #1 (eastern wind-rich corridor), Region #2 (Tarim Basin, west–east increasing wind power density), Region #3 (northern valleys), and Region #4 (mountainous areas with weakest wind power density). Peaks-over-threshold analysis revealed 10~30-year return levels varying regionally, with 10-year return level for Node #1 reaching Beaufort Scale 11 but only Scale 6 for Node #4. Since 2001, EWS occurrences increased, with Nodes #2–4 showing doubled 10-year event occurrences in 2012–2023. Events exhibit consistent afternoon peaks and spring dominance (except Node #2 with summer maxima). Such long-term trends and diurnal and seasonal preferences of EWS could be partly explained by diverging synoptic drivers: orographic effects and enhanced pressure gradients (Node #1 and #3) associated with Ural blocking and polar vortex shifts, both showing intensification trends; thermal lows in the Tarim Basin (Node #2) accounting for their summer prevalence; boundary-layer instability that leads to localized wind intensification (Node #4). The results suggest the necessity of region-specific forecasting strategies for wind energy resilience. Full article

High-order linear polarization (LP) modes and vortex beams carrying orbital angular momentum (OAM) are highly useful in various fields. High-order LP modes provide higher thresholds for nonlinear effects, reduced sensitivity to distortions, and better energy extraction in high-power lasers. OAM beams are useful in optical communication, imaging, particle manipulation, and fiber sensing. The ability to switch between these mode outputs enhances system versatility and adaptability, supporting advanced applications both in research and industry. This paper presents the design of a 19 × 1 photonic lantern capable of outputting 19 LP modes and 16 OAM modes with low loss. Using the beam propagation method, we simulated and analyzed the mode evolution process and insertion loss, and we calculated the transmission matrix of the photonic lantern. The results indicate that the designed device can efficiently evolve into these modes with a maximum insertion loss not exceeding 0.07 dB. Furthermore, an adaptive control system was developed by introducing a mode decomposition system at the output and combining it with the Stochastic Parallel Gradient Descent (SPGD) + basin hopping algorithm. Simulation results show that this system can produce desired modes with over 90% mode content, demonstrating promising application prospects in switchable high-order mode systems. Full article

This paper presents a rapid approach for the dynamic separation of radial polarization (R-pol) and azimuthal polarization (A-pol) components in circular Airy vortex beams (CAVBs) by utilizing the linear electro-optic (EO) effect in uniaxial crystals. By applying an external electric field along the z-axis of a strontium barium niobate (SBN) crystal, tunable spatial separation of the R-pol and A-pol components is achieved. Under positive electric fields, the crystal maintains negative uniaxial properties with increased birefringence, extending the focal separation distance. Conversely, negative electric fields initially reduce the birefringence of the crystal; further increases in negative field strength will transition the crystal to a positive uniaxial state, subsequently enhancing birefringence and restoring focal separation. Experimental simulations demonstrate a focal separation of 1.4 mm at ±15 kV/mm, with R-pol focusing first at +15 kV/mm and A-pol preceding at −15 kV/mm. The polarization distributions at the foci confirm the successful separation of the two components. This approach overcomes the static limitation of conventional polarization splitters in separating R-pol and A-pol components, showing significant potential for optical manipulation, high-resolution imaging, and quantum information processing. Full article

Following a very cold first half of the Arctic stratosphere winter of 2024–2025, the stratospheric polar vortex weakened from late February. The increase in the polar lower stratosphere temperature led to a decrease in the polar stratospheric cloud (PSC) type I (NAT) volume from ~80 million km³ to zero. The polar vortex weakening and temperature increase continued in early March, when major sudden stratospheric warming occurred. Although the polar cap total column ozone (TCO) significantly increased during this period, an ozone mini-hole formed over Scandinavia and northwestern Russia, with TCO values as low as 220–240 Dobson units, according to satellite observations and ground-based measurements over St. Petersburg and Moscow on 5–6 March 2025. Chemistry-transport model calculations using MERRA2 reanalysis data were performed to investigate the role of chemical ozone depletion and dynamical processes in the low TCO values in early March. Model experiments show that dynamical processes played a predominant role in the formation of low TCO values, but the role of chemical processes was not negligible. Associated with the TCO anomaly, the difference relative to the standard ozone level in the UV indices over Moscow, St. Petersburg and Helsinki reached up to 60–100%. Full article

Vortex electromagnetic (EM) waves exhibit spiral wavefront phase distributions, owing to their orbital angular momentum (OAM). Thus, the scattered waves from targets contain OAM characteristics, demonstrating novel scattering properties. Although researchers have carried out both theoretical and experimental studies on the target scattering characteristics of vortex EM waves, a comprehensive and standardized characterization framework is still lacking. This paper proposes and defines an EM vortex scattering matrix (EVSM), which can be used as a characterization method for the target scattering characteristics in the OAM dimension of vortex EM waves. Since vortex EM waves carry both OAM and spin angular momentum (SAM), the EM vortex-polarization joint scattering matrix (EVPJSM) is defined by extending EVSM. This joint matrix simultaneously describes the target scattering characteristics in both OAM and SAM dimensions of vortex EM waves. And it can offer a thorough framework of target scattering characteristics for arbitrary OAM–SAM combinations in new-dimensional EM waves. Numerical simulations are performed to compute each element in EVPJSM for two typical targets under twelve different pairs of OAM modes and two SAM polarization combinations. The numerical results can be used as an example of the characterization method in new dimensions for the targets’ scattering characteristics. Full article

This paper proposes a co-aperture reflective metasurface that successfully generates four-channel Bessel vortex beams with equal divergence angle in both Ka and Ku bands. Initially, a frequency-selective surface (FSS) is employed to suppress inter-unit crosstalk. Subsequently, modified cross-dipole metasurface units are implemented using spin-decoupling theory to achieve independent multi-polarization control. Through theoretical calculation-based divergence angle engineering, the dual-concentric-disk structure integrated with multi-polarization control demonstrates enhanced aperture utilization efficiency compared to conventional partitioning strategies, yielding high-purity equal-divergence-angle Bessel vortex beams across multiple modes. Finally, experiments on the metasurface fabricated via printed circuit board (PCB) technology verify that the design simultaneously generates x-polarization +1 mode and y-polarization +2 mode equal divergence angle Bessel vortex beams in the Ku band and ±3 mode beams in the Ka band. Vortex beam divergence angles remain stable at 9° ± 0.5° under diverse polarization states and modes, with modal purity reaching 65–80% at the main radiation direction. This work provides a straightforward implementation method for generating equal-divergence-angle vortex beams applicable to Orbital Angular Momentum (OAM) multimode multiplexing and vortex wave detection. Full article

Using multiple reanalysis datasets, this study investigates the decadal variability in the relationship between Northeast Pacific Sea surface temperature (SST) and Arctic stratospheric ozone (ASO), with a focus on the role of atmospheric dynamics in mediating this connection. A significant decadal shift is identified around the year 2000, characterized by a weakening of the previously strong negative correlation between January–February SST anomalies and February–March ASO. Prior to 2000 (1980–2000), warm SST in the northeastern Pacific suppressed upward planetary wave propagation, resulting in decreased stratospheric wave activity and a weakened Brewer–Dobson circulation. The weakened BD circulation reduced poleward transport of tropical ozone and heat, yielding a colder, ozone-poor polar vortex. The strong relationship enabled skillful seasonal predictability of ASO using SST precursors in a linear regression model. However, post-2000 (2001–2022), the weakened planetary wave response to SST anomalies resulted in a breakdown of this relationship, yielding non-significant predictive skill. The findings highlight the non-stationary nature of ocean-stratosphere coupling and underscore the importance of accounting for such decadal shifts in climate models to improve projections of Arctic ozone recovery and its surface climate impacts. Full article

An environmentally friendly and highly sensitive analytical method for the determination of the dye Eosin Y (EY) was developed utilizing vortex-assisted liquid–liquid microextraction based on deep eutectic solvents (DESs), combined with fluorescence detection (LPME-FLD). The extraction efficiencies of conventional solvents and various DES systems, composed of tetrabutylammonium bromide (TBAB) and alcohols (hexanol, octanol, and decanol) in different ratios, were systematically compared. DFT calculations provided insights into the most stable forms of EY in solvents of varying polarity. Theoretical Hansen solubility parameters and the COSMO-RS solvation model were applied to assess extraction efficiency. Hansen parameters were obtained via semiempirical PM7 calculations, while BP86/def2-TZVPD DFT computations were employed within the openCOSMO-RS framework. The developed method exhibited a linear calibration range between 0.1 and 130 µg·L⁻¹, with a high correlation coefficient (R² = 0.9982). The limit of detection (LOD) was established at 0.028 µg·L⁻¹. Method precision and repeatability were confirmed over two days, with relative standard deviations (RSDs) ranging from 1.1% to 2.7% and with recoveries between 99.0% and 106.2%. The proposed analytical approach was successfully applied to the determination of EY in real water samples, demonstrating both its practical applicability and alignment with green chemistry principles. Full article

Due to global warming, extreme temperature events have become increasingly prevalent, posing significant threats to both socioeconomic development and human safety. While previous studies have extensively examined the influence of individual climatic circulation systems on extreme temperature, the combined effects of multiple concurrent circulation patterns remain poorly understood. Using daily temperature data from 29 meteorological stations in Chongqing (1960–2019), this study employs linear trend analysis, correlation analysis, and random forest (RF) models to analyze spatiotemporal variations in the intensity and frequency of extreme temperature. We selected 21 climate indicators from three categories—atmospheric circulation, sea surface temperature (SST), and sea-level pressure (SLP)—to identify the primary drivers of extreme temperatures and quantify their respective contributions. The key findings are as follows: (1) All extreme intensity indices exhibited an increasing trend, with the TXx (annual maximum daily maximum temperature) showing the higher trend (0.03 °C/year). The northeastern region experienced the most pronounced increases. (2) Frequency indices also displayed an upward trend. This was particularly evident for the TD35 (number of days with maximum temperature ≥35 °C), which increased at an average rate of 0.16 days/year, most notably in the northeast. (3) The Western Pacific Subtropical High Ridge Position Index (GX) and Asia Polar Vortex Area Index (APV) were the dominant climate factors driving intensity indices, with cumulative contributions of 26.0% to 33.4%, while the Western Pacific Warm Pool Strength Index (WPWPS), Asia Polar Vortex Area Index (APV), North Atlantic Subtropical High Intensity Index (NASH), and Indian Ocean Warm Pool Strength Index (IOWP) were the dominant climate factors influencing frequency indices, with cumulative contributions of 46.4 to 49.5%. The explanatory power of these indices varies spatially across stations, and the RF model effectively identifies key circulation factors at each station. In the future, more attention should be paid to urban planning adaptations, particularly green infrastructure and land use optimization, along with targeted heat mitigation strategies, such as early warning systems and public health interventions, to strengthen urban resilience against escalating extreme temperatures. Full article