Synchronous Events Research Articles

Photon-Assisted Synchronization of Molecular Electrochemical Oscillators

Abstract Formation of hydronium and carbonate ions from carbon dioxide in the aqueous phase is a reversible process and can both produce and consume ions. These equilibrium reactions represent molecular electrochemical oscillators in pure water. Reversible switching of ionic dynamics is a chaotic process, which is influenced by the CO2 level, temperature and other factors. As demonstrated in previous works, weak variations of magnetic fields induce different electrochemical reactivity and generate ionic waves caused by mutual synchronization of molecular oscillators. Such waves correlate between transparent electrochemical cells, suggesting macroscopic mechanisms for their interaction. This work explores these observations by monitoring the high-resolution ionic dynamics and temperature of independent fluidic cells with electrochemical impedance spectroscopy. Synchronization effects are shown to occur primarily in the CO2 dissolving scenario on the 3-10 minute scale. Without CO2 access, mutual synchronization is either non-existent or negligible. Maximal correlations with r>0.9 are achieved between 4-6 cells. The number of synchronization events is about five times lower when cells are separated between non-transparent containers. To explain such results, we consider the hypothesis of molecular quantum networks that operate with spin conversion of water isomers, investigation of these mechanisms can lead to new quantum sensing technologies.

A review of synchronization of extreme precipitation events in monsoons from complex network perspective

A review of synchronization of extreme precipitation events in monsoons from complex network perspective

Building a Multilake Paleoseismometer for the Xianshuihe Fault (Tibetan Plateau, China)

AbstractThe Xianshuihe fault, located in the southeastern Tibetan Plateau, stands as one of the most active faults in China. As assessing earthquake hazard relies on access to long‐term paleoseismological archives, this paper seeks to optimize the interpretation of paleoseismological records. We retrieved nine sediment cores from three lakes over a 30 km fault segment. Earthquake‐related deposits were identified through grain‐size analysis, XRF core scanning, and SEM observations of thin sections. Age models based on short‐lived radionuclides correlate these events with historical earthquakes, which are recorded with varying sensitivities to seismic intensity across the three lakes. We developed a code that evaluates the plausibility of rupture scenarios against sedimentary evidence: Each site is used as a binary paleoseismometer, indicating whether or not an earthquake reached a local intensity threshold. The combined evidence from the three sites allows to evaluate rupture scenarios on the Xianshuihe fault, according to rupture length‐magnitude scaling laws and intensity prediction equations. The most probable scenarios allow to discriminate the rupture area and magnitude range providing a good agreement with historical reconstructions. Our work demonstrates the potential of combining earthquake records to infer the magnitude and rupture zone of paleo‐earthquakes, even with a limited data set. Our approach, applicable across diverse geological settings and timescales, offers enhanced precision in understanding long‐term paleoseismology covering multiple earthquake cycles. However, establishing the synchronicity of events in such an active area—where earthquake return times are typically <100 years—demands highly accurate age models, which remains challenging.

Making Meaningful Places: Augmented Reality for Digital Placemaking in Clearwater, Florida

Enhancing public art installations with augmented reality (AR) merges the physical and digital worlds and creates a strong sense of place attachment in urban settings. AR is an established tool for digital placemaking, which is a participatory form of embodied space-based social practice. While there is disagreement over whether digital placemaking is best achieved through organic engagement with locative media, deliberate urban planning initiatives, or a combination of both, it is increasingly clear that well-designed AR can impact how citizens perceive and engage with their physical surroundings and can invigorate urban spaces. In this article, we explore the design and development of ARTours Clearwater, an AR app that was developed as part of a city-led public art initiative aimed at increasing foot traffic and enlivening a downtown district through the creation of vivid, memorable, “imageable” spaces. The app development workflow encompassed terrestrial lidar scanning of the murals, the identification of tracking images in Vuforia, the development and scaling of digital animations in Unity, and onsite testing to evaluate environmental conditions. The project came to fruition at a public launch, which promoted novel forms of people-place interactions by bringing together multiple stakeholder groups in a synchronous event that enlivened the city’s downtown.

Dry soil moisture on the Tibetan plateau drives synchronous extreme heatwaves in Europe and East Asia

Recently, extreme heatwaves have frequently concurrently swept across Europe and East Asia, causing severe cascading socioeconomic consequences. However, the nonlinear synchronization relationship between these heatwaves and their underlying physical mechanisms remains poorly understood. Utilizing the event synchronization climate network method, atmospheric dynamic diagnostics, and numerical experiments, we revealed robust synchronization between heatwaves over Europe and East Asia, strongly associated with dry soil moisture conditions over the Tibetan Plateau from the preceding winter to summer. Dry soil moisture triggers an equivalent barotropic anticyclone north of the Tibetan Plateau, coinciding with the subtropical westerly jet waveguide and initiating circumglobal atmospheric Rossby waves propagating westward and eastward. Consequently, an equivalent barotropic anticyclone develops over Europe. These anticyclones induce simultaneous heatwaves across Europe and East Asia by increasing downward solar radiation and adiabatic sinking, amplified by positive land-atmosphere feedback. Our findings significantly enhance the understanding and predictive capabilities of these synchronous heatwaves across Eurasia.

Propagations From Extreme Integrated Vapor Transport to Extreme Precipitation Events in North America

AbstractExtreme integrated vapor transport (IVT) is a crucial driving factor of extreme precipitation events (EPEs). This paper presents a complex network‐based characterization of propagations from extreme IVT to EPEs. Specifically, the propagations are tracked from extreme IVT to EPEs by event synchronization; and then the source zones of extreme IVT contributing to EPEs are identified by two‐layer complex network. A case study is devised for North America based on the daily NCEP/NCAR Reanalysis 1 from 1948 to 2021. Overall, eight communities of EPEs are identified: the west coast of United States (US) tend to receive substantial EPEs from the Pacific Ocean; the Gulf of Alaska tends to receive oceanic EPEs propagating inland; western Canada typically experiences large amount of out tendencies and the EPEs tend to accumulate in the Baffin Island and Labrador Peninsula; the southeastern US and the northern Great Plains tend to experience northward propagations from Mexico. Along the west coast of North America, the propagations from extreme IVT to EPEs typically originate from the eastern North Pacific between 160°W and 110°W, and make landfalls in 4 days. These propagations are influenced by anomalous cyclonic circulations developing over the Gulf of Alaska forced by eastward Rossby waves. The coincidence rate of these propagations with atmospheric rivers is, respectively, 85.31% in autumn, 91.35% in winter, 73.94% in spring, and 64.52% in summer. Overall, the observed propagations from extreme IVT to EPEs yield insights into the mechanism of atmospheric moisture transport and the predictability of precipitation.

Characterisation and synchronisation of a netted software defined radio radar

AbstractThe present work intends to characterise the combination of two netted software defined radios (SDR) and different radio frequency (RF) front‐ends installed in them, together with a two‐stratum time dissemination and synchronisation system. A modified implementation of the Network Time Protocol is used as coarse event synchronisation for either SDR back‐end. The White rabbit light embedded node implementation of the commonly known white rabbit synchronisation system (IEEE 1588 PTP‐2019) or arbitrary wave form generators are used as fine time dissemination system for either SDR. The resulting netted transceiver system is intended to compose a demonstrator for proof‐of‐concept experiments. The findings presented in this article show that the chosen combination of hardware and software is suitable for radar applications operating within L‐, S‐ and C‐bands. A channel coherency throughout the network with a relative modified Allan deviation of less than 80 fs for averaging intervals of 1 s, a phase noise better than −118 dBc/Hz at 10 Hz frequency offset and a fractional frequency lower than was measured. Within a single transceiver node, a fractional frequency lower than and phase noise of −124 dBc/Hz at 10 Hz frequency offset were measured as well. Multistatic radar systems exploit wide spatial diversity to enhance target detection and tracking, albeit with increased complexity when compared to a monostatic configuration. To exploit these benefits, all participating transceiver nodes within the netted radar need to synchronise to a common time base . The achieved synchronisation level increases the accuracy with which the chain of timed events at the transmitter and at the receiver side occur, intending to maximise the signal‐to‐noise ratio available at the receiver. The Universal software radio peripheral model X310 with two different daughterboard models as RF front‐end was used as SDR on either radar node. A network combining data and synchronisation purposes allowed the radar nodes under test to operate synchronously. The two‐stratum synchronisation system used glass fibres between 2 m and 5 km of length or coaxial cables with 2 m in length for network traffic, time and frequency dissemination purposes. The multiple RF front‐ends were stimulated by means of arbitrary waveform generators with calibrated traceability. Up‐chirp and sinusoid waveforms were used as stimuli for measuring the offset of either channel with regards of to ultimately estimate the achievable coherency limits of the system under test. Both analogue and digital evaluation methods were considered.

Improved chronostratigraphy and fine-tuned timing for Late Triassic palaeoenvironmental changes in SW Britain using coupled magnetic polarity and carbon isotope stratigraphy

Understanding the synchronicity of global climatic, environmental, and biotic events around the Norian-Rhaetian boundary (NRB) is problematic because of major international differences in biochronology. We instead use magnetostratigraphic and global carbon isotopic changes to produce more precise global correlation. This work focusses on the base and top of the Rhaetian, with principal age control from a new late Norian to latest Rhaetian magnetostratigraphy from Lavernock (southern Wales) which can be directly correlated to the proposed NRB sections at Pignola Abriola (Italy) and Steinbergkogel (Austria). A disconformity exists in the Lavernock section in its late Norian part (Branscombe Mudstone Formation), but the NRB interval is largely complete. The magnetostratigraphy and a composite δ13Corg stratigraphy from three British sections, demonstrate synchronous changes in both terrestrial and marine records. This analysis indicates the older proposed definition of the NRB from Steinbergkogel is in the upper few metres of the Branscombe Mudstone Formation, while the younger NRB definition from Pignola Abriola is in the upper parts of the Blue Anchor Formation. The latest Rhaetian magnetostratigraphy from Lavernock records reverse magnetochrons UT26r and UT28r which closely pre-date and post-date the widely recognised Marshi and Spelae carbon isotope excursions, respectively. Magnetochrons UT28r and UT27r were previously recognised at St Audrie's Bay (SW England), with relationships to the Newark Supergroup which tightly constrain the first phase of CAMP eruptions to overlap the Spelae excursion. The carbon isotope excursions present in the Blue Anchor Formation lacustrine successions, demonstrate the likely atmospheric, and global spread of these perturbations.

CRITICAL CAUSAL EVENTS IN SYSTEMS BASED ON CQRS WITH EVENT SOURCING ARCHITECTURE

Context. The article addresses the problem of causal events asynchrony which appears in the service-oriented information systems that does not guarantee that the events will be delivered in the order they were published. It may cause intermittent faults occurring at intervals, usually irregular, in a system that functions normally at other times. Objective. The goal of the work is the comparison and assessment of several existing approaches and providing a new approach for solving the causal events synchronization issue in application to the systems developed using Command Query Responsibility Segregation (CQRS) with Event Sourcing (ES) architecture approach. Methods. Firstly, the method of estimation of the likelihood of causal events occurring within the systems as the foundation for choosing the solution is suggested. Based on the results of the analysis of several projects based on CQRS with ES architecture it shows that the likelihood of critical causal events depends on the relationships among entities and the use-cases connected with the entities. Secondly, the Container of Events method, which represents a variation of event with full causality history, adapted to the needs of CQRS with ES architecture systems, was proposed in this work. The variants of its practical implementation have also been discussed. Also, the different solutions, such as Synchronous Event Queues and variation of Causal Barrier method were formalized and assessed. Thirdly, the methods described have been discussed and evaluated using performance and modification complexity criteria. To make the complexity-performance comparative assessment more descriptive the integrated assessment formula was also proposed. Results. The evaluation results show that the most effective solution of the issue is to use the Container of Events method. To implement the solution, it is proposed to make the modifications of the Event Delivery Subsystem and event handling infrastructure. Conclusions. The work is focused on the solution of the critical causal events issue for the systems based on CQRS with ES architecture. The method of estimation of the likelihood of critical causal events has been provided and different solutions of the problem have been formalized and evaluated. The most effective solution based on Container of Events method was suggested.

Spatiotemporal desynchronization in the propagation from meteorological to soil moisture drought in the Loess Plateau, China

Study RegionThe Loess Plateau (LP) of China Study FocusMeteorological drought (MD) would propagate to soil moisture drought (SMD) with spatiotemporal desynchronization. The spatial desynchronization between them has frequently been ignored in previous studies due to limitation of identified droughts, which did not consider their 3-dimensional (3D, i.e. longitude, latitude and time) properties. This study presents a 3D perspective on the spatiotemporal desynchronization in the propagation from meteorological to soil moisture drought in the the Loess Plateau (LP) of China, using an improved drought matching method. Event Synchronization (ES) is extended to determine temporal linkage of the two types of droughts and spatial connection is tested using overlapping area. New Hydrological Insights for the RegionThe results showed that: (1) the improved method is reasonable for identifying MDs that trigger SMDs, down to specific clusters; (2) 8 SMDs preceded MDs 1 month, while approximately 79 % of SMDs did not recover after the determination of MDs; (3) severity of MD is an impact factor on recovery lag, while antecedent soil moisture dominates onset lag with the relative importance of approximately 50 %; and (4) incompletely overlap in migration trajectory between the two types of droughts was mainly caused by temperature, followed by antecedent soil moisture and potential evapotranspiration, with relative importance of 55 %, 14 % and 12 %, respectively.

Synchronization evaluation of digital twin for a robotic assembly system using computer vision

Traditional production processes are profoundly transforming in the era of Industry 4.0 and smart manufacturing. Smart manufacturing, a core element of Industry 4.0, employs advanced technologies such as automation, robotics, AI, big data analytics, and machine learning to boost productivity and manufacturing performance. Central to this evolution is the Digital Twin (DT), digital replicas of physical assets that blend real-time data with advanced analytics and simulations. Ensuring synchronization between the digital replica and its physical counterpart is crucial for the success of Digital Twins. This paper addresses the challenge of achieving and quantifying synchronization within DTs, focusing on replicating physical system behaviour and measuring deviations or delays. The study delves into the critical aspects of synchronization within digital twin applications, focusing on its implications for a robotic assembly system. The research successfully harnessed YOLOv8 to facilitate real-time event tracking and synchronization characterization, highlighting the potential of computer vision in enhancing synchronization accuracy and, consequently, the efficiency and reliability of manufacturing processes.

Concurrent droughts across Major River Basins of the World modulated by El Niño–Southern Oscillation

Droughts are among the costliest natural disasters with far-reaching impacts. Focusing on the influence of El Niño–Southern Oscillation (ENSO) on worldwide droughts, this paper presents a formulation of the complex network of concurrent droughts across the Major River Basins (MRBs) of the World. Specifically, concurrent droughts are measured by event synchronization and interconnections of concurrent droughts are determined by significance test. Event coincidence analysis is incorporated into interconnections to quantify the effects of El Niño and La Niña events. A case study is devised for the 3-monthly standardized precipitation index (SPI) of Global Drought and Flood Catalogue during the period from 1950 to 2016. The results highlight that owing to the synchronization of droughts, there exist nine communities of the MRBs, each covering MRBs across different continents. While the correlation between SPI and ENSO exhibits mixed patterns for MRBs grouped by continent, there exist distinct patterns of correlation for MRBs grouped by community. Overall, 28.88% of concurrent droughts tend to be modulated by El Niño events, especially over MRBs in South-West Pacific, South Africa, northern South America and South Asia. In the meantime, 23.51% of concurrent droughts tend to be modulated by La Niña events, especially over MRBs in the United States, southwestern South America, northern China and Central Asia. The modulation of El Niño and La Niña is confirmed by composite analysis of SPI and detailed analysis of the Yangtze River Basin. Overall, the complex network provides useful information for drought forecasting and disaster mitigation.

Late mesozoic exhumation of silurian – Devonian and permian Ni-Co sulfide deposits in the East Kunlun orogenic belt: Constraints from zircon fission track ages

Ni-Co sulfide deposits of late Silurian – early Devonian and Permian ages hosted within in basic-ultrabasic rock bodies in the East Kunlun orogenic belt have been extensively investigated. Nevertheless, we have only a limited understanding of the history and dynamics of uplift, exhumation, and tectonic deformation of the basic-ultrabasic ore-bearing rock bodies of these Ni-Co sulfide deposits. We used the zircon fission track ages of seven samples obtained from basic-ultrabasic ore-bearing rocks to determine the timing of the exhumation of these Ni-Co sulfide deposits. Combining our results with published data on the timing of orogenesis, cooling events, magmatic activities, and basin infilling in adjacent areas, we conclude the following: 1) The ZFT ages obtained in this study indicate the exhumation during 169.6 ± 5.5–142.2 ± 3.2 Ma; 2) Combined with previous results, our data indicate that the exhumation during the Jurassic – Cretaceous occurred across a large area along the East Kunlun orogenic belt to the Alxa block; 3) The synchroneity of orogeny, magmatic activity, and basin infilling events suggests that the late Mesozoic exhumation was a geomorphological response to the Lhasa-Qiangtang collision driven by the breakup of Gondwanaland.

Pine woodland fire dynamics mirror industrial history at New River Gorge National Park and Preserve, West Virginia, USA

Fire is an important biophysical process in pine (Pinus) and mixed pine-oak (Quercus) forests and woodlands across the Central Appalachian Mountains. Decades of fire exclusion, however, particularly on public lands, have resulted in a well-documented homogenization of species composition and forest structure. Our objective was to inform management and restoration efforts by expanding on previous dendroecological research at New River Gorge National Park and Preserve and adjacent Babcock State Park in southern West Virginia. Specifically, we assessed pine woodland fire activity in the context of local industrial history, land management, and regional drought. Samples cut from 110 fire-scarred pine trees, distributed across four sites, were used to develop a fire-scar record that spans the period 1842–2010; however, sample depth diminishes rapidly before the 1860s. Fires occurred frequently and extensively in the early–mid 20th century, coinciding with peak coal production and population density. Eleven major fires, or years when at least two trees and 25 % of samples recorded a fire scar at an individual site, were documented in the tree-ring record, but none occurred during the federal land management era (1978–present). Synchronous fire events recorded at two or more sites were associated with drier than average September–May (‘dormant season’) climate conditions. Our results indicate that, since the late 19th century, fire activity in pine woodlands at the New River Gorge has been driven primarily by human ignitions associated with industrial activities, and that periods of drought have amplified landscape-scale fire occurrence. Land managers should consider these historical fire patterns when developing restoration strategies that may include prescribed fire, thinning treatments, and managed wildfires.

Lysophospholipid remodeling mediated by the LplT and Aas protein complex in the bacterial envelope

Lysophospholipid transporter LplT and acyltransferase Aas consist of a lysophospholipid-remodeling system ubiquitously found in gram-negative microorganisms. LplT flips lysophospholipids across the inner membrane, which are subsequently acylated by Aas on the cytoplasmic membrane surface. Our previous study showed that the proper functioning of this system is important to protecting E. coli from phospholipase-mediated host attack by maintaining the integrity of the bacterial cell envelope. However, the working mechanism of this system is still unclear. Herein, we report that LplT and Aas form a membrane protein complex in E. coli which allows these two enzymes to cooperate efficiently to move lysophospholipids across the bacterial membrane and catalyze their acylation. The direct interaction of LplT and Aas was demonstrated both in vivo and in vitro with a binding affinity of 2.3 μM. We found that a cytoplasmic loop of LplT adjacent to the exit of the substrate translocation pathway plays an important role in maintaining its interaction with Aas. Aas contains an acyl-acyl carrier protein synthase domain and an acyl-transferase domain. Its interaction with LplT is mediated exclusively by its transferase domain. Mutations within the three loops near the putative catalytic site of the transferase domain, respectively, disrupt its interaction with LplT and lysophospholipid acylation activity. These results support a hypothesis of the functional coupling mechanism, in which LplT directly interacts with the transferase domain of Aas for specific substrate membrane migration, providing synchronization of substrate translocation and biosynthetic events.

Symposium 4: Reflections on Hybridity in the Malta Networked Learning Forum 2021

This paper discusses the practicality, successes and possible failures of the Malta Networked Learning (NL) Forum held in May 2021. The forum was held in a hybrid synchronous face-to-face and virtual context, with a wide range of international participants, planned at short notice due to continuing uncertainty of Covid-19 restrictions. The paper outlines contexts and understandings of hybridity in both events and pedagogical approaches, noting varying definitions and concepts that may utilise this term to indicate forms of barrier breaking, overcoming limitation or supporting flexibility. Further context highlights recent literature concerning other digitally hybrid conference events, the need for which have been accelerated in light of the Covid-19 pandemic and additional considerations of climate change for reducing the carbon footprint of academic communities. Discussion leads to the type of hybridity implemented for the Malta NL Forum in May 2021, where pandemic international travel restrictions, local regulations and participant planning uncertainty required the adoption of a face-to-face and virtual synchronous event. The local organising team (authoring this paper) provides commentary to critically reflect on the strengths and weaknesses of the modality adopted. Emphasis is placed on designing for hybridity in future events, to improve planning and organisation for flexible and agile awareness to support the full range of participants in hybrid contexts and activities. The paper attempts to support those whose role is to convene and host similar events aiming to foster rewarding engagement for those participating, both presenting as well as attending.

Deliberative Behaviors and Prefrontal-Hippocampal Coupling are Disrupted in a Rat Model of Fetal Alcohol Spectrum Disorders.

Fetal alcohol spectrum disorders (FASDs) are characterized by a range of physical, cognitive, and behavioral impairments. Determining how temporally specific alcohol exposure (AE) affects neural circuits is crucial to understanding the FASD phenotype. Third trimester AE can be modeled in rats by administering alcohol during the first two postnatal weeks, which damages the medial prefrontal cortex (mPFC), thalamic nucleus reuniens, and hippocampus (HPC), structures whose functional interactions are required for working memory and executive function. Therefore, we hypothesized that AE during this period would impair working memory, disrupt choice behaviors, and alter mPFC-HPC oscillatory synchrony. To test this hypothesis, we recorded local field potentials from the mPFC and dorsal HPC as AE and sham intubated (SI) rats performed a spatial working memory task in adulthood and implemented algorithms to detect vicarious trial and errors (VTEs), behaviors associated with deliberative decision-making. We found that, compared to the SI group, the AE group performed fewer VTEs and demonstrated a disturbed relationship between VTEs and choice outcomes, while spatial working memory was unimpaired. This behavioral disruption was accompanied by alterations to mPFC and HPC oscillatory activity in the theta and beta bands, respectively, and a reduced prevalence of mPFC-HPC synchronous events. When trained on multiple behavioral variables, a machine learning algorithm could accurately predict whether rats were in the AE or SI group, thus characterizing a potential phenotype following third trimester AE. Together, these findings indicate that third trimester AE disrupts mPFC-HPC oscillatory interactions and choice behaviors.

Virtual Time III, Part 3: Throttling and Message Cancellation

This is Part 3 of a trio of papers that unify in a natural way the two historically distinct parallel discrete event synchronization paradigms, optimistic and conservative, combining the best properties of both into a single framework called Unified Virtual Time (UVT) . In this part we survey the synchronization effects that can be achieved by restricting to corner cases the relationships permitted among the control variables, GVT , CVT , TVT , and LVT , which were defined in Part 1 . We also survey various throttling policies from the literature and describe how they can be implemented in UVT by controlling the value of TVT , including policies that can take advantage of rollback in addition to LP blocking. A significant result is a new category of efficient and higher precision throttling algorithms for optimistic execution that are based on optimistic lookahead , defined in a way that is symmetric to what we now call the conservative lookahead information that is traditionally used for conservative synchronization. Finally, we present a novel algorithm allowing the choice between lazy and aggressive cancellation to be made on a message-by-message basis using either external logic expressed in the model code, or policy code internal to the simulator, or a mixture of both.

Investigating the spatial propagation patterns of meteorological drought events and underlying mechanisms using complex network theory: A case study of the Yangtze River Basin, China

The spatial propagation patterns of meteorological drought events (MDEs) and underlying mechanisms contribute to elucidating and forecasting drought evolution. In this study, gridded MDEs in the Yangtze River Basin (YRB) throughout the entire year, wet season and dry season were extracted from 3-month Standardized Precipitation Evapotranspiration Index (SPEI-3) series. Event synchronization (ES) and complex networks (CN) were employed to construct the MDE synchronization networks and MDE spatial propagation networks for various periods. The former were utilized to identify MDE synchronized subregions where MDEs co-occur and co-evolve in the YRB, while the latter were used to quantify the MDE spatial propagation patterns over both the basin and its subregions. The driving mechanisms behind MDE spatial propagation were further investigated by diagnosing the concomitant drought-inducing climate systems. The findings reveal the presence of four MDE synchronized subregions during the wet season and five subregions during the entire year and dry season. These subregions exhibited distinct spatial propagation patterns of MDEs, aligning with overall findings across the YRB. Notable differences were observed between wet and dry seasons, with various subregions exhibiting distinctive spatial propagation patterns during each season. These patterns are driven by variations in the controlling atmospheric circulation systems, leading to anomalies of wind patterns and moisture distribution, ultimately resulting in deficient moisture supply. The variations of tropical sea surface thermal conditions, influences of the Tibetan Plateau and MDE self-propagation triggered by land–atmosphere feedback are considered as three primary influencing factors for MDE spatial propagation in the YRB.

Drought and wetness events encounter and cascade effect in the Yangtze River and Yellow River Basin

Under the background of global change, the multivariate attributes, multi-temporal and multi-watershed regional characteristics of extreme drought and flood disasters are significant. It is very important to identify the drought and wetness encounter law and spatial cascade effect in the source region-upper-middle-lower reaches of the basin. In this paper, the Yangtze River and Yellow River basins are taken as the research objects. Based on the standardized precipitation index (SPI) characterizing meteorological drought and wetness and the standardized runoff index (SRI) characterizing hydrological drought and wetness, the evolution law of extreme drought and flood events in the source region-upper-middle-lower reaches of the two basins is analyzed. On this basis, the correlation analysis and transfer function analysis are used to explore the response relationship and lag effect between the two in different partitions. A two-dimensional joint distribution model is constructed by Copula function to quantitatively analyze the joint probability of drought and wetness encounters of 9 combined events, and to deeply analyze the impact of different drought and wetness encounter scenarios. The results show that: from 1957 to 2020, the two basins showed a trend from drought to wet. The SPI-12 in the Yellow River Basin ranged from-1.57 to 1.32, and that in the Yangtze River Basin ranged from-1.24 to 1.11. The severity of drought and wetness in the Yellow River Basin was higher than that in the Yangtze River Basin; The correlation coefficients between SPI and SRI in the source-upper-middle-lower reaches of the Yellow River (Yangtze River) were 0.78 (0.76), 0.23 (0.73), 0.44 (0.55) and 0.23 (0.63), respectively. The correlation degree of meteorological-hydrological drought and wetness in the Yangtze River Basin was significantly higher than that in the Yellow River Basin. The average probability of synchronous combination events of drought and wetness in the two basins is greater than 51.43 %. The probability of drought in the Yellow River Basin is greater than that of flood, while the Yangtze River Basin is the opposite. In the same drought and wetness scenario, an average of 54.1% of the event pairs were aggravated by disasters, and more than 52 % of the events in the wetness-drought scenario had obvious drought mitigation effects. The research results can provide important support for improving the early warning and risk management of river basin disasters.