Search Results (290)

Stratospheric polar vortex (SPV) stretching events are typically of 1–2 weeks in duration when the SPV is elongated and locally extends anomalously south into lower latitudes. Such events are often associated with extreme cold over the Great Plains to southern and eastern states of the US. Here, we present an observational study of SPV stretching events. First, empirical orthogonal function (EOF) analyses were performed for daily geopotential height fields (in the Northern Hemisphere domain) at 500 and 100 hPa levels, respectively. The second modes (EOF2) are identified to be associated with SPV stretching events. Second, the evolution and morphology of geopotential height anomalies are described based on composite averaging over all individual events. The retrograding 500 hPa EOF2 positive circulation pattern may lead to SPV stretching (i.e., 100 hPa EOF2) and a cold wave in North America. Long-duration EOF2+ events (principal component amplitude > 1 for longer than 5 days) are associated with a Siberian/East Asian trough, while short events are not. The frequency of long-duration 500 hPa EOF2+ occurrence is found to be 1.1 and 2.6 per season (November to March) following Octobers of low and high snow cover extent (SCE) over Eurasia, respectively, or high and low autumn sea ice concentration (SIC) from the Greenland Sea to the Kara Sea, respectively. The occurrences of long events are more likely initiated when the zonal-mean zonal wind (60–70° N) is reduced in the lower stratosphere, with the Siberian trough deepened and the Alaskan ridge enhanced (i.e., amplified stationary eddies). The anomalies grow rapidly after initial perturbations and move westward, leading to a deep trough anomaly and a “wavier” jet stream over North America. Meanwhile in the stratosphere, an enhanced ridge over the Bering Strait and Alaska is accompanied by a downstream trough, which extends to the surface over Canada. It is suggested that the frequency of North American cold waves may be modulated by the interannual variations of snow cover and sea ice through perturbations to the zonal mean zonal wind and stationary eddies. Full article

Vertical shear of the zonal wind across the equatorial tropopause over the Indian Ocean to the Maritime Continent is caused by a combination of the quasi-biennial oscillation (QBO) of the stratosphere and the seasonal cycle and interannual variability of the upper troposphere. The Madden–Julian Oscillation (MJO) has been previously observed to be more active during the easterly than the westerly phase of the QBO. Kelvin waves interacting with the background flow explain most of the propagation characteristics of the MJO in the equatorial upper troposphere. This work assesses the hypothesis that Kelvin wave propagation under conditions of easterly wind in both the upper troposphere and stratosphere maintains the upper tropospheric MJO circulation, but that this signal is disrupted with westerly wind shear that likely includes critical layers that would prevent Kelvin wave energy from passing. Linear regression of reanalysis data against an MJO index shows more coherent downward propagating Kelvin waves during easterly shear and no Kelvin-wave-like signal near the tropopause during conditions expected to include critical layers there. Historical analysis of this vertical shear shows that it is the primary focus of enhanced MJO variance with the easterly QBO, yielding the seasonally enhanced signal December through February and the erratic variability from year to year due to tropospheric contributions to shear. A wavenumber frequency spectrum analysis of lower stratospheric zonal wind shows that power shifts from high to low frequency between QBO westerly to easterly phases, consistent with Kelvin waves propagating at the phase speed range of the MJO during easterly QBO. Full article

Although large-scale wind and solar power provide green electricity, their intermittency and reverse-peak characteristics pose severe challenges to the secure operation of power systems. Pumped storage hydropower (PSH), as the most mature and economically attractive large-scale energy storage technology, enables temporal energy shifting and serves as a core flexible resource for smoothing renewable fluctuations and peak load shaving. In a new power system dominated by renewables, the reverse distribution between resources and loads gives rise to a typical “three-zone coexistence” pattern, i.e., renewable-rich zones, load centers, and hub zones coexist. However, existing research lacks in-depth modeling of zonal functional differences and fails to reveal the coupling mechanism between inter-zonal section constraints and the temporal energy behavior of pumped storage plants (PSPs). To address these gaps, this paper proposes a zonal-differentiated optimal dispatch model for multiple PSPs considering inter-zonal section constraints. The model establishes a “zonal role–PSP behavior” matching mechanism, assigning differentiated objectives and operational constraints to PSPs located in different zones, and thereby automatically generating charging/discharging strategies that match each zone’s functional positioning. It integrates section power flow constraints with the energy balance equations of PSPs in each zone into a unified framework, quantifying how section congestion restricts the “cross-zone energy shifting” efficiency of PSPs. Furthermore, a congestion-driven adaptive rule is derived from the above coupling framework. Case studies on a three-zone test system demonstrate that the proposed model effectively reduces wind and solar curtailment, alleviates section overloading, and lowers total operating costs, while the adaptive rule provides real-time decision support for dispatchers. The proposed model is applicable to power grids at various levels exhibiting the “three-zone coexistence” characteristic, offering theoretical support and a practical tool for the joint dispatch of multiple PSPs under high-penetration renewable energy integration. Full article

HY–4A is China’s first ocean salinity remote-sensing satellite, launched into orbit in November 2024 and currently in operational service. The LASMR (L-Band Aperture Synthesis Microwave Radiometer) is the L-band synthetic aperture radiometer onboard the HY–4A satellite. This study validates the LASMR Level-2 SSS (sea surface salinity) product using in situ salinity observations from Argo floats, covering the period from November 2024 to December 2025. Global analysis indicates that the LASMR SSS retrieval uncertainties show a distinct zonal distribution, which primarily reflects the impact of sea surface temperature (SST) and sea surface wind speed on SSS retrieval accuracy. A lower SST reduces the sensitivity of brightness temperature (TB) to SSS variations, and a high wind speed degrades the sea surface roughness correction. Both factors lead to increasing uncertainties in SSS retrieval. Furthermore, atmospheric parameters including water vapor content and precipitation also affect the SSS retrieval uncertainty. The influence of water vapor may originate from its coupling with SST/wind speed and inherent uncertainties in the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data. The effect of precipitation is more complex: it increases ocean TB through rain-induced surface freshening and additional rain-induced roughening, which aliases into the satellite signal. Moreover, precipitation-enhanced vertical salinity gradients amplify the vertical representativeness error arising from the depth difference between satellite sensing and Argo measurements. Meanwhile, impacted by land brightness temperature contamination and radio-frequency interference (RFI), the SSS retrieval accuracy of HY–4A decreases significantly in coastal waters compared with the open ocean. Since the traditional buoy–satellite dual-matching method tends to overestimate uncertainties in satellite data, an Argo/HY–4A/SMAP (Soil Moisture Active Passive) triple-collocation dataset is used to estimate the LASMR SSS retrieval uncertainties. The triple-collocation method yields robust uncertainty estimates for both satellites (HY–4A and SMAP) over the global ocean and high-salinity-variability regions. In conclusion, the global uncertainty of the HY–4A LASMR SSS product is 0.35 psu. These results provide a reference for future product refinement and improvements in HY–4A SSS retrieval algorithms. Full article

The “spin-up” problem, in which convection-permitting models require hours to develop realistic clouds from large-scale initial fields, critically limits short-term severe weather forecasting. Cloud analysis can serve as a feasible approach to directly assimilate hydrometeor information from remote sensing retrievals. In this study, we leverage multi-source remote sensing data, including three-dimensional mosaic radar reflectivity, hourly averaged FY-2G satellite brightness temperature (black-body temperature, TBB), and FY-2G total cloud water products, within a stepwise cloud analysis initialization scheme. The scheme is implemented in a convective-scale ensemble forecasting system (CMA-Meso, 3 km resolution) for a heavy rainfall event. For each ensemble member, three-dimensional hydrometeor increments are independently generated from these remote sensing retrievals and gradually introduced over the first ten time steps, ensuring smooth coordination with the model’s dynamic thermal framework. Quantitatively, the scheme reduces near-surface Continuous Rank Probability Score (CRPS) errors, improves the overall predictive skill by 2.6–7.9% (maximum at the 12 h spin-up period), and increases ensemble spread by 2–5.8%, mitigating under-dispersion. Probabilistic precipitation forecasts show uniform area under the relative operating characteristic curve (AROC) improvements across all thresholds, 1.16–5.77% for light rain, 3.03–8.97% for moderate rain, and 6.00–12.07% for heavy rain, with these maxima consistently occurring at the 12 h spin-up time. Although Brier scores are marginally larger, these AROC gains confirm the enhanced discrimination of convective rainfall. At 500 hPa, CRPS reductions of 7.1–15.6% emerge after 24 h (largest 15.6% for geopotential height at 24 h), zonal wind CRPS is reduced by 2.2% at 12 h, and ensemble spread increases by 3.1–7.0% for all three variables. These improvements, particularly the pronounced benefits during the initial 12 h, demonstrate that the remote sensing-driven cloud analysis effectively shortens spin-up. Mechanistically, the gains arise from physically coordinated hydrometeor-latent heat perturbations and subsequent cloud radiation feedback that continuously regulate thermal-dynamic structures. This study establishes that assimilating diverse remote sensing data via cloud analysis is an effective approach for overcoming spin-up challenges in convective-scale ensembles. Full article

Clarifying how vegetation restoration regulates wind erosion, sediment redistribution, and soil improvement is essential for ecological management in desert photovoltaic power stations. This study was conducted in a high-clearance flexible-support photovoltaic power station at the edge of the Kubuqi Desert. Three restoration measures were compared: reed mulch combined with Atriplex canescens planting along the panel front edge (M1), A. canescens planting along the panel front edge alone (M2), and reed mulch combined with grass seeding (M3). The panel front-edge zone (QY), under-panel zone (BX), and pedestal zone (JZ) were used as functional units to analyze surface sediment grain-size characteristics, soil moisture, soil nutrients, windbreak efficiency, aerodynamic roughness length, and cumulative sand-fixing efficiency. All restoration measures altered the surface sediment structure, with Mz ranging from 2.005 to 2.364 and D₀ from 1.459 to 1.935. Soil moisture ranged from 0.58% to 4.34%, with the highest value occurring in the 20–30 cm layer of QY under M1. M1 also showed higher soil organic matter in QY and JZ, reaching 1.87 and 1.16 g·kg⁻¹, respectively. Windbreak efficiency decreased with height under all measures. M1 maintained the highest and most stable values, decreasing only from 61.16% at 10 cm to 55.52% at 100 cm. The total cumulative sand-fixing efficiency was also highest under M1 (233.66%), while M2 (215.05%) and M3 (214.58%) showed comparable total effects but different zonal responses. Wind-eroded materials shifted from fine-sand dominance toward a higher relative contribution of medium sand, reflecting the reduction in finer transported fractions rather than true grain coarsening. The novelty of this study lies in linking wind-erodible sediment redistribution, soil water and nutrient responses, and windbreak–sand-fixing performance across internal functional zones of a flexible-support photovoltaic array. These results indicate that vegetation restoration in desert photovoltaic power stations should be configured by functional zone, with composite interception at the panel front edge, structural maintenance in the under-panel zone, and cover-based sand trapping in deposition-prone areas. Full article

Increasing greenhouse gas concentrations are placing severe pressure on the Earth system, particularly on the ocean, which plays a vital role in carbon and heat uptake, and overall climate regulation. Consequently, the ocean is experiencing an accelerated warming, leading to an increase in the occurrence of extreme seawater temperature events, called Marine Heatwaves (MHWs). According to the most common definition, an MHW event is identified when local temperatures exceed the 90th percentile threshold of the climatology for at least five consecutive days. In this study, the definition was modified by calculating both the mean and the 90th percentile of SST over the entire available historical period (1982–2022), rather than using a fixed 30-year baseline. While MHWs can develop as a function of multiple drivers (including subsurface heat re-emergence, anomalously warm water masses, ocean heat advection, reduced vertical mixing, and mixed-layer stratification associated with surface heat gain), this study focuses on synoptic-scale atmospheric conditions associated with MHW occurrence and characteristics in the North Atlantic basin, from 1982 to 2022, with the objectives of identifying spatial-temporal trends of MHWs, examining the atmospheric conditions associated with their occurrence and exploring their relationship with prevalent climate variability modes. The results show positive trends in MHW frequency, duration, and intensity, albeit characterised by significant zonal and meridional variability, with noticeable differences between composite patterns of frequency and maximum intensity, according to the prevailing North Atlantic Oscillation (NAO) mode. The annual NAO appears to modulate the spatial distribution of MHWs, with its positive phase favouring MHWs in mid-latitude regions, while the negative phase impacts subpolar and tropical regions. Furthermore, concerning case-specific events, the stationarity of high-pressure systems, with weak pressure gradients, reduced wind speeds and increased solar radiation appears to be associated with the occurrence of the analysed events, while atmospheric instability appears to signal their decline, likely linked to enhanced wind-induced ocean mixing. Full article

Summertime westward-to-eastward zonal wind reversal near the mesopause is a key manifestation of wave–mean flow interaction in the mesosphere and lower thermosphere. We examined this zonal wind reversal over Langfang, China, during May–July 2024 using co-located MF and meteor–radar winds together with SD-WACCM output. The reversal height and vertical shear near the reversal height were obtained from a linear fitting. Both radars showed pronounced temporal dependence for the zonal wind-reversal height, with a higher height at the beginning of summer, which decreased from May to July. The MF radar placed the transition slightly higher than meteor radar, both of which are confined to the mesopause region. The SD-WACCM output showed clear zonal wind reversal, but the reversal heights were between MF and meteor observations. Moreover, the decreasing trend of the zonal wind-reversal height in the SD-WACCM output was less evident than in radar observations. Nevertheless, the zonal wind reversal exhibited clear diurnal variations. The total zonal wind tendency due to gravity wave-breaking in the SD-WACCM output was utilized to diagnostically analyze the reasons, wherein diurnal variations in the wind-reversal height corresponded well to the diurnal variations in gravity wave-dragging. Monthly model diagnostics further showed the positive strengthening of gravity wave drag near 80–90 km from May to July. Our analysis showed that the temporal variation in the background flow and the reversal layers during 2024 were intimately related to gravity wave momentum deposition locally and globally. Full article

The atmospheric boundary layer (ABL) has strong diurnal variability, but routine radiosonde launches at 00:00 and 12:00 UTC cannot fully resolve its daily evolution. This study develops and evaluates a 13-year (2007–2019) hourly ABL profile dataset using Aircraft Meteorological Data Relay (AMDAR) observations from 42 selected European airports, and applies it to characterize airport-scale diurnal, seasonal, and regional variations in ABL structure. AMDAR-derived temperature and wind profiles were validated against collocated radiosonde observations by season, pressure layer, and airport–radiosonde distance. Errors decrease for shorter separation distances and lower-tropospheric layers. For separations < 50 km and pressures > 850 hPa, spring, summer, autumn, and winter RMSEs are 0.9/1.0/1.4/1.2 K for temperature, 1.7/2.0/1.9/1.9 m/s for zonal wind, and 1.4/1.6/1.9/1.6 m/s for meridional wind. Hourly AMDAR profiles reveal distinct diurnal ABL evolution at airport scale. Seasonal ABL height (ABLH) composites are mainly 250–900 m, with available nighttime and early-morning values of about 300–450 m and spring–summer afternoon maxima of 800–900 m at far-inland airports. Coastal airports show weaker daytime growth, mostly below 600–650 m. These results demonstrate AMDAR’s value as a supplementary profile dataset for characterizing European airport-scale ABL structure and diurnal variability. Full article

The reduction of carbon dioxide related to the energy sector is one of the greatest challenges of this century. To ensure a proper transition towards a sustainable electric power system, innovative solutions are fundamental for the efficient integration of renewable energy sources. Hybrid Renewable Energy Systems (HRES) play a crucial role in this scenario; they can ensure a stable and reliable electricity supply thanks to the combination of different renewable technologies, particularly thanks to the integration of storage systems. However, the optimal sizing process of such systems is a complex challenge due to the multiple uncertainties that can be present, involving demand fluctuations and electricity zonal price variations. The aim of this work was to develop a Mixed-Integer Linear Programming (MILP) optimization approach for the robust sizing of a HRES under multiple sources of uncertainty. The developed hybrid model consists of a wind farm, a photovoltaic (PV) plant, a Battery Energy Storage System (BESS), and an industrial load with the entire infrastructure for connection to the national power grid. Additionally, the model includes the capability to manage the over-generation of renewable resources through curtailment mechanisms. The objective of the sizing tool is to minimize the Net Present Cost (NPC) of the plant, while ensuring the reliability of the system. The developed tool can represent a useful assistant for the evaluation of different possible configurations, helping the decision-making process during the design of a HRES. The results will show the best trade-off between economic and reliability aspects, highlighting the impact that the uncertainty has on the optimal size of the plant. In particular, the best configuration analyzed is able to reduce the NPC of more than 50% compared to a plant with a single renewable source. Full article

This paper investigates the impact of renewable energy source (RES) integration on the Sicilian transmission network, considering the commissioning of new Mediterranean interconnections, namely the TUN-ITA and the Tyrrhenian Link. The expansion of transmission infrastructures and the increasing penetration of RES require an assessment of the Sicilian power system’s capability to accommodate high levels of power injection. This study was carried out in collaboration with the Italian transmission system operator Terna S.p.A. and the University of Palermo. It aims to evaluate the evolution of transmission line loading under future RES integration scenarios consistent with grid connection requests submitted to Terna and with national energy policy targets. The proposed methodology integrates micro-zonal assessments of wind and solar potential, estimation of capacity factors, development of RES capacity expansion scenarios, and steady-state power flow simulations. The simulations were performed using WinCreso^® software version 7.69 for three time horizons: 2028, 2029, and 2035. The results show the most congested transmission lines and the network areas most exposed to congestion. The analysis provides operational insights for prioritizing grid reinforcement measures and proposes a replicable methodological framework for other transmission system operators facing similar RES integration challenges. Full article

This study presents a nonlinear optimization framework for the hourly economic dispatch of interconnected multi-zone power systems integrating thermal, hydroelectric, wind, photovoltaic, and battery energy storage resources. The proposed formulation explicitly models zonal power balance, interzonal power exchange, thermal ramp-rate limits, battery state-of-charge dynamics, storage operating bounds, and hydroelectric energy quotas in order to minimize total system operating cost while preserving technical feasibility. The methodology was implemented in MATLAB and applied to a three-zone interconnected test system under two operating conditions: autonomous zonal operation and coordinated interconnected operation with battery storage support. The results show that the coordinated strategy reduces total operating cost from USD 8.23 million/day to USD 6.60 million/day, corresponding to a 19.8% reduction and an estimated annual saving of USD 595 million. In parallel, the optimized interconnected dispatch increases wind generation from 14.46 to 16.44 GWh/day and reduces thermal generation from 8.12 to 6.08 GWh/day, thereby improving the effective use of renewable resources. A complementary sustainability assessment further shows that coordinated operation increases the renewable share from 71.81% to 78.68%, decreases the carbon intensity of supplied electricity from 189.4 to 146.3 kgCO₂-e/MWh, and yields estimated avoided emissions of 1241.0 tCO₂-e/day. These findings demonstrate that the joint use of interzonal coordination and battery energy storage provides simultaneous economic, operational, and environmental benefits, thereby supporting sustainability-oriented operation of modern multi-zone power systems. Full article

For the environment and the daily life of urban settlements, in the context of contemporary challenges, severe meteorological events rank second worldwide. Therefore, these events tend to become a real threat to human society and to specific economic activities. The main objective of this study is to analyze the spatio-temporal evolution of severe meteorological events in urban environments and to assess their relationship with atmospheric circulation regimes and urban thermal conditions. The analysis focuses on five types of severe events (significant atmospheric precipitation, hail, strong winds, tornadic structures, and cloud-to-ground lightning) recorded in 11 cities located in the historical region of Muntenia, Romania, over the period 2014–2024. The methodological framework is based on three complementary components. First, a new database was developed by integrating information from multiple sources, including the National Meteorological Administration (ANM), the European Severe Storms Laboratory (ESSL), international databases, and validated media reports, with spatio-temporal filtering and aggregation into synoptic episodes. Second, atmospheric circulation regimes were identified using ECMWF ERA5 reanalysis data, based on geopotential height anomalies at the 500 hPa level, allowing the classification of large-scale synoptic patterns. Third, urban thermal conditions were assessed using the ECMWF CERRA regional reanalysis dataset, which provides high-resolution air temperature data, enabling the analysis of urban–peri-urban thermal contrasts and the estimation of the urban heat island effect. The results highlight a total of 997 severe meteorological events, of which 253 (25.6%) were recorded in the analyzed urban areas, 85 (15.9%) in other towns, and 583 (58.5%) in rural areas. The analysis reveals pronounced interannual and intraseasonal variability, as well as distinct spatial clustering patterns, particularly in urban and peri-urban zones. Among the circulation regimes, the Zonal Regime exhibits the highest event rate, suggesting increased favorability for severe weather occurrence, while other regimes show weaker or even inhibitory effects. In addition, most severe events were associated with positive urban–peri-urban temperature contrasts, indicating an active contribution of the urban heat island effect. By combining observational data, synoptic-scale analysis, and urban-scale thermal assessment, this study provides an integrated regional perspective on severe meteorological events and contributes to the enrichment of data sources in the region, while improving the understanding of their dynamics in urban environments affected by data limitations. Full article

This study investigates subauroral phenomena during the main phase of the 10 May 2024 geomagnetic storm using a combination of ground-based observations from the WD IZMIRAN observatory (magnetometer, ionosonde, and all-sky imager) and Global Self-consistent Model of the Thermosphere, Ionosphere, Protonosphere (GSM TIP) simulations. During 18:00–20:00 UT, we identified the simultaneous occurrence of ionospheric signatures of Polarization Jets (PJ)/Sub-Auroral Ion Drifts (SAID) and Strong Thermal Emission Velocity Enhancement (STEVE) over Kaliningrad, consistent with previously reported PJ/SAID identification from DMSP drift velocity measurements. This identification is supported by: (1) characteristic purple emissions (clearly visible in all three channels) moving rapidly westward; (2) U-shaped structures in ionogram sequences; (3) the reproduction of supersonic westward plasma drifts within a narrow latitudinal band by the first-principles model; and (4) observed and simulated significant Ne depletion. The estimated ion drift velocity from all-sky imaging (assuming an emission altitude of 200 km) is consistent with GSM TIP simulations, which predicted PJ/SAID velocities of ~750 m/s driven by a latitudinally narrow (~3°) but longitudinally extended (>50°) poleward electric field (40 mV/m). Simulations reveal that this PJ/SAID phenomenon causes a reversal of the zonal thermospheric wind at 250 km and induces Ne disturbances across the 200–700 km altitude range. The electron temperature enhancement (up to 1500 K) exhibits a “falling drop” shape, peaking at 350 km, while ion heating exceeds 150 K. The neutral temperature shows a dual response: frictional heating at 120–160 km and localized cooling at 175–250 km due to drop in electron density. Additionally, an increase in atomic oxygen concentration was predicted within the 90–200 km range across the PJ/SAID longitudinal sector. Full article

The significant interannual variability in Madden–Julian Oscillation (MJO) intensity remains incompletely understood. Empirical orthogonal function (EOF) analysis reveals that the first three leading EOF modes of the annual mean MJO intensity are significantly correlated with the Quasi-Biennial Oscillation (QBO), Eastern Pacific El Niño-Southern Oscillation (ENSO), and Central Pacific ENSO. Focusing on the distinct EOFs related to three key tropical interannual variabilities, we conduct an investigation into the potential governing processes through which the changes in background mean states impact MJO intensity based on the MJO moisture mode theory. Observations suggest that the accumulation of moist static energy (MSE) during MJO moistening phases and its dissipation during drying phases play a crucial role in regulating MJO amplitude. At the interannual timescale, regions characterized by positive EOF values display positive (negative) MSE tendency anomalies during MJO moistening (drying) phases, leading to amplified MSE accumulation (dissipation) throughout the MJO lifecycle and subsequently facilitating an increase in MJO amplitude. Conversely, regions with negative EOF values exhibit opposing trends. Further analysis reveals that these MSE tendency anomalies are mainly associated with the zonal advection term, which is influenced by interannual changes in the background mean MSE and low-level winds. The spatial pattern of the background mean MSE is strongly linked to sea surface temperature (SST) anomalies, with low-level background winds aligning well with the horizontal gradients of SST anomalies. Full article