Rapid Variability Research Articles

Rapid variability of Markarian 421 during extreme flaring as seen through the eyes of XMM–Newton

ABSTRACT By studying the variability of blazars across the electromagnetic spectrum, it is possible to resolve the underlying processes responsible for rapid flux increases, so-called flares. We report on an extremely bright X-ray flare in the high-peaked BL Lacertae object Markarian 421 (Mrk 421) that occurred simultaneously with enhanced γ-ray activity detected at very high energies by First G-APD Cherenkov Telescope on 2019 June 9. We triggered an observation with XMM–Newton, which observed the source quasi-continuously for 25 h. We find that the source was in the brightest state ever observed using XMM–Newton, reaching a flux of 2.8 × 10−9 $\mathrm{erg\, cm^{-2}\, s^{-1}}$ over an energy range of 0.3–10 keV. We perform a spectral and timing analysis to reveal the mechanisms of particle acceleration and to search for the shortest source-intrinsic time-scales. Mrk 421 exhibits the typical harder-when-brighter behaviour throughout the observation and shows a clock-wise hysteresis pattern, which indicates that the cooling dominates over the acceleration process. While the X-ray emission in different sub-bands is highly correlated, we can exclude large time lags as the computed z-transformed discrete correlation functions are consistent with a zero lag. We find rapid variability on time-scales of 1 ks for the 0.3–10 keV band and down to 300 s in the hard X-ray band (4–10 keV). Taking these time-scales into account, we discuss different models to explain the observed X-ray flare, and find that a plasmoid-dominated magnetic reconnection process is able to describe our observation best.

Observations of magnetic reconnection in the deep solar atmosphere in the Hεline

Context.Magnetic reconnection in the deep solar atmosphere can give rise to enhanced emission in the Balmer hydrogen lines, a phenomenon known as Ellerman bombs (EBs). It is most common to observe EBs in the Hαand Hβspectral lines. High-quality shorter-wavelength Balmer line observations of EBs are rare, but have the potential to provide the most highly resolved view on magnetic reconnection.Aims.We aim to evaluate the Hε3970 Å line as an EB diagnostic by analyzing high-quality observations in different Balmer lines.Methods.Observations of different targets and viewing angles were acquired with the Swedish 1-m Solar Telescope. These observations sample EBs in different environments: active regions, the quiet Sun, and the penumbra and moat of a sunspot. We employed an automated detection method for quiet-Sun EBs based onk-means clustering.Results.Ellerman bombs in the Hεline show similar characteristics as in the longer-wavelength Balmer lines: a higher intensity than in the surroundings, rapid variability, and a flame-like morphology. In a 24 min quiet-Sun time series, we detected 1674 EBs in the Hεline. This is 1.7 times more EBs than in Hβ. The quiet-Sun EBs measured in Hεare very similar to those in Hβ: They have similar lifetimes and a similar area, brightness, and spatial distribution. Most of the EBs detected in Hεare closer to the limb than their Hβcounterparts because the Hεline core EB emission is formed higher in the atmosphere than the HβEB wing emission.Conclusions.We conclude that the Hεline is well suited for studying EBs, and consequently, for measuring the dynamics of magnetic reconnection in the solar atmosphere at the smallest scales. Our findings suggests that the deep atmosphere in the quiet Sun may host more than 750 000 reconnection events with an EB signature at any time. This is significantly more than what was found in earlier Hβobservations.

The internal Faraday screen of Sagittarius A*

We report on 85−101 GHz light curves of the Galactic Center supermassive black hole, Sagittarius A* (Sgr A*), observed in April 2017 with the Atacama Large Millimeter/submillimeter Array (ALMA). This study of high-cadence full-Stokes data provides new measurements of the fractional linear polarization at a 1−2% level resolved in 4 s time segments, and stringent upper limits on the fractional circular polarization at 0.3%. We compare these findings to ALMA light curves of Sgr A* at 212−230 GHz observed three days later, characterizing a steep depolarization of the source at frequencies below about 150 GHz. We obtain time-dependent rotation measure (RM) values, with the mean RM at 85−101 GHz being a factor of two lower than that at 212−230 GHz. Together with the rapid temporal variability of the RM and its different statistical characteristics in both frequency bands, these results indicate that the Faraday screen in Sgr A* is largely internal, with about half of the Faraday rotation taking place inside the inner 10 gravitational radii, contrary to the common external Faraday screen assumption. We then demonstrate how this observation can be reconciled with theoretical models of radiatively inefficient accretion flows for a reasonable set of physical parameters. Comparisons with numerical general relativistic magnetohydrodynamic simulations suggest that the innermost part of the accretion flow in Sgr A* is much less variable than these models predict; in particular, the observed magnetic field structure appears to be coherent and persistent.

Study of the Rapid Variability of a Dwarf Nova SS Cyg at Different Brightness Levels

Study of the Rapid Variability of a Dwarf Nova SS Cyg at Different Brightness Levels

Intranight Variability of Ultraviolet Emission from High-z Blazars

Rapid intranight variability of continuum and polarization in blazars is a valuable tool for probing the beaming of a relativistic jet and the associated population of the relativistic particles. Although such intranight variability in the rest-frame optical continuum has been extensively studied, there is a scarcity in the rest-frame ultraviolet (UV), where the variability might be caused by a secondary population of relativistic particles. To address this gap, we recently reported, for the first time, an intranight variability study of a sample of high-z blazars (Chand et al., 2022), with the monitored optical radiation is being their rest-frame UV radiation. Here, we discuss in detail the implications of this investigation, including a proper comparison of high-z blazar samples with fractional optical polarization (popt) lower and greater than 3%. In this context, we also report an intranight variability study of an additional high-z blazar at z = 2.347, namely J161942.38+525613.41, monitored over three sessions, each lasting approximately five hours. Our investigation does not reveal any compelling evidence for a stronger intranight variability of the UV emission in high polarization blazars, in contrast to the blazars monitored in the rest-frame blue-optical. We also discuss this trend in the light of the suggestion that the synchrotron radiation of blazar jets in the UV/X-ray regime may arise from a relativistic particle population different from that radiating up to near-infrared/optical frequencies.

Cellulose acetate/metal-organic framework composite beads with macroporous adsorption channels as a novel hemoadsorbent for effective virus capture.

Due to their rapid spread, high variability, and drug-resistant strains, new viral infections are continuously emerging. A lack of effective antiviral drugs and vaccines, resulting in disease and death, has significant socioeconomic consequences. Hemoperfusion can effectively adsorb and remove toxins from the blood, thus purifying the blood and serving as an acute treatment. Therefore, the aim of this study was to construct adsorbents to selectively remove viruses from the blood to quickly treat pathogen infection. We reported on new metal-organic framework (MOF)-polymer beads based on MIL-53(Al) and cellulose acetate (CNC), which were prepared by a one-step phase inversion method and applied as a viral hemo-adsorbent for the first time. The characterization results demonstrated that MIL-53(Al) was well dispersed in the CNC matrix. The adsorption results demonstrated that the capture efficiency of the human immunodeficiency virus (HIV) could exceed 99.93%, and the corresponding infectious titer decreased by approximately 103 times in clinical application. Moreover, CNC/MIL-53 exhibited low hemolysis ratios and good anticoagulant properties. Furthermore, molecular dynamics simulations revealed that the interplay of hydrogen bonding was the governing physisorption mechanism. Overall, CNC/MIL-53 could serve as a new type of hemoperfusion adsorbent for virus removal from blood and provide a new treatment pathway to mitigate epidemics.

On joint analysing <i>XMM-NuSTAR</i> spectra of active galactic nuclei

A recently released <i>XMM-Newton</i> note revealed a significant calibration issue between nuclear spectroscopic telescope array (<i>NuSTAR)</i> and <i>XMM-Newton</i> European Photon Imaging Camera (EPIC) and provided an empirical correction to the EPIC effective area. To quantify the bias caused by the calibration issue in the joint analysis of <i>XMM-NuSTAR</i> spectra and verify the effectiveness of the correction, in this work, we perform joint-fitting of the <i>NuSTAR</i> and EPIC-pn spectra for a large sample of 104 observation pairs of 44 X-ray bright active galactic nuclei (AGN). The spectra were extracted after requiring perfect simultaneity between the <i>XMM-Newton</i> and <i>NuSTAR</i> exposures (merging Good Time Intervals, GTIs from two missions) to avoid bias due to the rapid spectral variability of the AGN. Before the correction, the EPIC-pn spectra are systematically harder than the corresponding <i>NuSTAR</i> spectra by <inline-formula><tex-math id="M1">\begin{document}$\Delta \varGamma \sim 0.1 $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0160_M1.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0160_M1.png"/></alternatives></inline-formula>, subsequently yielding significantly underestimated cutoff energy <i>E</i><sub>cut</sub> and the strength of reflection component <i>R</i> when performing joint-fitting. We confirm that the correction is highly effective and can commendably erase the discrepancy in best-fit <i>Γ</i>, <i>E</i><sub>cut</sub>, and <i>R</i>. We thus urge the community to apply the correction when joint-fitting <i>XMM</i>-<i>NuSTAR</i> spectra, but note that the correction is limited to 3–12 keV and therefore not applicable when the soft X-ray band data are included. Besides, we show that as merging GTIs from two missions would cause severe loss of <i>NuSTAR</i> net exposure time, in many cases, joint-fitting yields no advantage compared with utilizing <i>NuSTAR</i> data alone. We finally present a technical note on filtering periods of high background flares for <i>XMM-Newton</i> EPIC-pn exposures in the Small Window mode.

Трансформаційні процеси в менеджменті підприємств в умовах війни

The article discusses the transformation processes that have taken place in the management of enterprises in extremely changing conditions of their functioning, which is war. For sustainability and development, these processes require, in particular, rapid adaptation, revision of the following: paradigms of management, security, personnel policy, information flows, business processes and business models; implementation of the principles of inclusiveness and accessibility, cost optimization; introduction of modern digital technologies; increase of productivity. The aim of the article is to substantiate and systematize the transformation processes of enterprise management during the wartime. To achieve this goal, the following tasks have been performed: the main problems in the management of enterprises that hinder their development in wartime have been systematized and characterized; the main blocks that unite the transformation processes in the management of enterprises during wartime are allocated on the basis of an analysis of the experience of various Ukrainian and international companies, this will allow other economic entities to lead their enterprises to sustainability, success, and efficiency. As result of the study, the authors determined that the main challenge in management in peacetime and in wartime is the rapid variability of factors of external influence, which leads to ultra-risky managerial decisions. During the war, it is difficult to foresee all sources of risks in management decisions that affect the business processes of the enterprise. At that, challenges appear quickly due to the variability of external factors, which leads to the rapid adaptation of managerial decisions and the need for their urgent solution. The loss of planning ability directly affects the decrease in the efficiency of the enterprise. Therefore, enterprises are trying to form certain patterns to stabilize their activities in extremely changing conditions of their functioning. Obviously, management has become the key instrument in this. The ability to make management decisions quickly, adapt to changing external factors, and implement high-quality communication with the team are crucial for success. Despite the lack of a one-size-fits-all approach, adhering to these core principles helps leaders navigate wartime and lead their businesses to sustainability, success, and efficiency.

Archaeology, rapid climate changes in the Holocene, and adaptive strategies

The article presents the concepts of repeating cycles of rapid climate variability in the Holocene, including rapid cooling cycles, cold events, ice-rafting events, and rapid climate change recorded in palaeoclimate archives. It also discusses the concepts of adaptation strategies embedded in the catastrophic scenarios of collapse on the one hand, and panarchy, resilience, and adaptation cycle on the other, i.e. the processes of transforming social hierarchical structures into dynamic, adaptive entities. In the rapid climate change series we focus on the 9.2 ka and 8.2 ka climate events associated with the Neolithisation process and the transition to farming. The 5.9 IRD event and/or period of rapid climate change from 6000–5200 cal yr BP are associated with the cultural, economic, and demographic collapse of the Early Neolithic Linear Pottery culture in central and western Europe. We also discuss the triad of recent weakening of North Atlantic ocean circulation, decreased solar activity, and the hypothesised transition to a cold period, the well-known historical scenario associated with the transition to Little Ice Age between 1450 and 1850.

Truncated, tilted discs as a possible source of Quasi-Periodic Oscillations

ABSTRACT Many accreting black holes and neutron stars exhibit rapid variability in their X-ray light curves, termed quasi-periodic oscillations (QPOs). The most commonly observed type is the low-frequency (≲10 Hz), type-C QPO, while only a handful of sources exhibit high-frequency QPOs (≳60 Hz). The leading model for the type-C QPO is Lense-Thirring precession of a hot, geometrically thick accretion flow that is misaligned with the black hole’s spin axis. However, existing versions of this model have not taken into account the effects of a surrounding, geometrically thin disc on the precessing, inner, geometrically thick flow. In Bollimpalli et. al 2023, using a set of GRMHD simulations of tilted, truncated accretion discs, we confirmed that the outer thin disc slows down the precession rate of the precessing torus, which has direct observational implications for type-C QPOs. In this paper, we provide a detailed analysis of those simulations and compare them with an aligned truncated disc simulation. We find that the misalignment of the disc excites additional variability in the inner hot flow, which is absent in the comparable aligned-disc simulations. This suggests that the misalignment may be a crucial requirement for producing QPOs. We attribute this variability to global vertical oscillations of the inner torus at epicyclic frequencies corresponding to the transition radius. This explanation is consistent with current observations of higher frequency QPOs in black hole X-ray binary systems.

On the impact of «red leak» of filters on brightness estimates of late stars using the example of observations of rapid variability of symbiotic stars

The results of modeling the dependence of the «red leak» of photometric filters on various factors (color index 𝑉 −𝑅, luminosity class, interstellar reddening, air mass and PWV) during observations of stars are presented. The error arising from not taking into account the «red leak» in the case of filters used on the 0.6-m telescope of the CMO SAI can amount to 0.6 𝑚 − 0.8 𝑚 for late stars. Algorithms for reducing observational data are presented for filters 𝑈 and 𝐵. The results of observations of the rapid variability of two symbiotic stars CH Cyg and SU Lyn with cold components of very late spectral types are presented. For CH Cyg, rapid variability was detected on both observation dates. Taking into account the «red leak» effect, the amplitude in the 𝐵 band was 0.10𝑚 on November 6, 2019 and 0.19𝑚 on December 15, 2022, with a characteristic variability time of about 20 minutes. For SU Lyn, no rapid brightness variability was detected in the 𝐵 band on February 2, 2023 (with an accuracy of 0.003𝑚)

Rapid seasonal changes in phenotypes in a wild Drosophila population

Seasonal environmental change is one of the most rapid and striking environmental variables. Although relatively rapid adaptation to environmental changes over several years or several decades has been described in many taxa, rapid responses to seasonal environments are delicate, and therefore, the detection of the evolutionary responses requires sensitive methods. In this study, we examined seasonal changes in phenotypes related to thermal tolerance and morphological traits of Drosophila lutescens collected at the spring and autumn periods from a single location. We first demonstrated that flies in the two seasonal periods were almost genetically identical using double-digest restriction site-associated DNA sequencing and analysis. Using an experimental design to eliminate the effect of possible confounding factors that influence phenotypes (i.e., maternal effects and the environmental conditions in which each phenotype was analyzed), we showed that the heat tolerance of D. lutescens was significantly higher in the autumn population than in the spring population. Furthermore, cold tolerance was slightly higher in the spring population than in the autumn one. Although wing length and thorax length did not change significantly between seasons, the ratio of wing length to thorax length changed significantly between them. These results suggest that seasonal environmental heterogeneity induces rapid phenotypic changes within a year. Finally, we discuss the possibility of rapid evolutionary responses to seasonal changes.

Formal derivation of a new sediment transport model using a multiscale procedure: Numerical Validation

We study in this work structures formed under a unidirectional flow. The main problem that addresses sediment transport by aquatic flow. We present the formal derivation of a new sediment transport model by using a multiscale procedure in time and space. We consider two non-miscible layers of different materials with physical properties by including friction. Interactions at the fluid-sediment interface and those internally sediment are also taken into account. The derived model is the Saint–Venant–Exner type obtained by coupling a Saint-Venant system governing the hydrodynamic component and an Exner equation describing the morphodynamical component. The first part of this work takes into account two major contributions namely the formal derivation of new unidirectional Saint–Venant–Exner model inspired by the work in Fernández-Nieto et al. (2017) and the introduction of a new multiscale parameterization in space-time characterized by the combination of classical variability and rapid variability of solutions. However, we have limited ourselves to the case of a first order approximation which does not include viscosity terms. Further analysis of the second order approach leading to a viscous model can be deduced from the work in Fernández-Nieto et al. (2013). We also propose a numerical study of the derived model. Thus, we develop finite volume numerical schemes. The numerical approach employs a Riemann solver, and various options ranging from an exact solver to an approximate Riemann HLL-type and HLLC-type solvers. We did some numerical tests leading to consistent and effective results.

On the Influence of ‘‘Red Leak’’ of Light Filters on the Brightness Estimates of Stars of Late Spectral Types Illustrated by the Observations of Rapid Variability of Symbiotic Stars

On the Influence of ‘‘Red Leak’’ of Light Filters on the Brightness Estimates of Stars of Late Spectral Types Illustrated by the Observations of Rapid Variability of Symbiotic Stars

The Rapid Optical Variability of the Nearby Radio-loud AGN Pictor A: Introducing the Quaver Pipeline for AGN Science with TESS

The sampling strategy of the Transiting Exoplanet Survey Satellite (TESS) makes TESS light curves extremely valuable for investigating the high cadence optical variability of active galactic nuclei (AGN). However, because the TESS instrument was primarily designed for exoplanet science, the use of the satellite for other applications requires careful treatment of the data. In this paper, we introduce Quaver, a new software tool designed specifically to extract TESS light curves of extended and faint sources presenting stochastic variability. We then use this new tool to extract light curves of the nearby radio-loud AGN Pictor A, and perform a temporal and power spectral analysis of its high-cadence optical variability. The obtained light curves are well fit with a damped random walk (DRW) model, exhibiting both stochastic AGN variations and flaring behavior. The DRW characteristic timescales are τ DRW ∼ 3–6 days during more quiet periods, and τ DRW ∼ 0.8 day for periods with strong flares, even when the flares themselves are masked from the DRW fit. The observed timescales are consistent with the dynamical, orbital, and thermal timescales expected for the low black hole mass of Pictor A.

Magnetized Accretion Disks with Outflows for Changing-look AGNs

Changing-look active galactic nuclei (CL-AGNs) challenge the standard accretion theory, owing to their rapid variability. Recent numerical simulations have shown that, for the sub-Eddington accretion case, the disk is magnetic pressure–dominated, thermally stable, and geometrically thicker than the standard disk. In addition, outflows were found in the simulations. Observationally, high blueshifted velocities absorption lines indicate that outflows exist in AGNs. In this work, based on the simulation results, we investigate the magnetic pressure–dominated disk, and find that the accretion timescale is significantly shorter than that of the standard thin disk. However, such a timescale is still longer than that of the CL-AGNs. Moreover, if the role of outflows is taken into account, then the accretion timescale can be shortened even further. By the detailed comparison of the theoretical accretion timescale with the observations, we propose that the magnetic pressure–dominated disk incorporating outflows can be responsible for the rapid variability of CL-AGNs.

Detection of X-ray/UV delay in NGC 4051 using AstroSat observations

ABSTRACT We study the connection between the variations in the far-ultraviolet (FUV), near-ultraviolet (NUV), and X-ray band emission from NGC 4051 using 4 d long AstroSat observations performed during 5–9 June 2016. NGC 4051 showed rapid variability in all three bands with the strongest variability amplitude in the X-ray band ($F_{\mathrm{ var}} \sim 37~{{\ \rm per\ cent}}$) and much weaker variability in the UV bands ($F_{\mathrm{ var}} \sim 3{\!-\!}5~{{\ \rm per\ cent}}$). Cross-correlation analysis performed using interpolated cross-correlation functions and discrete cross-correlation functions revealed a robust correlation (∼0.75) between the UV and X-ray light curves. The variations in the X-ray band are found to lead those in the FUV and NUV bands by ∼7.4 ks and ∼24.2 ks, respectively. The UV lags favour the thermal disc reprocessing model. The FUV and NUV bands are strongly correlated (∼0.9) and the variations in the FUV band lead those in the NUV band by ∼13 ks. Comparison of the UV lags found using the AstroSat observations with those reported earlier and the theoretical model for thermal reverberation timelag suggests a possible change in either the geometry of the accretion disc/corona or the height of the corona.

Photoproduction of P-wave doubly charmed baryon at future e+e− collider

The photoproduction of P-wave doubly charmed baryon (Ξcc) is investigated in the context of future high-energy and high-luminosity e+e− colliders. The direct photoproduction via the sub-process γ+γ→Ξcc+c¯+c¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\gamma +\\gamma \ o {\\Xi}_{cc}+\\overline{c}+\\overline{c} $$\\end{document} and the resolved channel γ+g→Ξcc+c¯+c¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\gamma +g\ o {\\Xi}_{cc}+\\overline{c}+\\overline{c} $$\\end{document} are considered. Within the framework of non-relativistic QCD, the calculation encompasses four P-wave (cc)-diquark configurations: cc3¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {(cc)}_{\\overline{\ extbf{3}}} $$\\end{document}[1P1], (cc)6[3P0], (cc)6[3P1] and (cc)6[3P2]. The two S-wave states, cc3¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {(cc)}_{\\overline{\ extbf{3}}} $$\\end{document}[3S1] and (cc)6[1S0], are also included for comparison. The cross sections, as well as the differential distributions involving transverse momentum, rapidity, and angular variables, have been computed. Numerical results reveal that the resolved photoproduction process plays a significant role and can provide dominant contributions. The photoproduction rate of the P-wave Ξcc is approximately one order of magnitude lower than that of the S-wave.

Key factors for quantitative precipitation nowcasting using ground weather radar data based on deep learning

Abstract. Quantitative precipitation nowcasting (QPN) can help to reduce the enormous socioeconomic damage caused by extreme weather. The QPN has been a challenging topic due to rapid atmospheric variability. Recent QPN studies have proposed data-driven models using deep learning (DL) and ground weather radar. Previous studies have primarily focused on developing DL models, but other factors for DL-QPN have not been thoroughly investigated. This study examined four critical factors in DL-QPN, focusing on their impact on forecasting performance. These factors are the deep learning model (U-Net, as well as a convolutional long short-term memory, or ConvLSTM), input past sequence length (1, 2, or 3 h), loss function (mean squared error, MSE, or balanced MSE, BMSE), and ensemble aggregation. A total of 24 schemes were designed to measure the effects of each factor using weather radar data from South Korea with a maximum lead time of 2 h. A long-term evaluation was conducted for the summers of 2020–2022 from an operational perspective, and a heavy rainfall event was analyzed to examine an extreme case. In both evaluations, U-Net outperformed ConvLSTM in overall accuracy metrics. For the critical success index (CSI), MSE loss yielded better results for both models in the weak intensity range (≤ 5 mm h−1), whereas BMSE loss was more effective for heavier precipitation. There was a small trend where a longer input time (3 h) gave better results in terms of MSE and BMSE, but this effect was less significant than other factors. The ensemble by averaging results of using MSE and BMSE losses provided balanced performance across all aspects, suggesting a potential strategy to improve skill scores when implemented with optimal weights for each member. All DL-QPN schemes exhibited problems with underestimation and overestimation when trained by MSE and BMSE losses, respectively. All DL models produced blurry results as the lead time increased, while the non-DL model retained detail in prediction. With a comprehensive comparison of these crucial factors, this study offers a modeling strategy for future DL-QPN work using weather radar data.

Quantitative Analysis of Climate Variability and Human Activities on Vegetation Variations in the Qilian Mountain National Nature Reserve from 1986 to 2021

Rapid climate variability and intense human activities generate obvious impacts on the Qilian Mountains ecosystem. The time series of fractional vegetation coverage (FVC) from 1986 to 2021 were used to quantify the impact of climate variability and human activities on vegetation variations in the Qilian Mountain National Nature Reserve (QMNNR), using 3147 land satellite images based on the Google Earth Engine cloud platform. The contributions of climate variability and human activities to FVC were quantified using multiple regression residual analysis. Partial correlation and correlation methods were used to quantify the impact of temperature, precipitation, and human activity footprints on FVC. The results showed that from 1986 to 2021, the increase rate of FVC was 1.7 × 10−3 y−1, and the high vegetation coverage of the FVC was mainly distributed in the southeastern part of the reserve. In contrast, the low vegetation coverage was mainly distributed in the northwest part of the reserve. The Mann–Kendall mutation test found that the year of 2009 was the year of the mutation. The growth rate of FVC from 2010 to 2021 was greater than that from 1986 to 2009. In addition, climate variability and human activities exhibited a remarkable spatial heterogeneity in FVC changes. Climate variability and human activities contributed 49% and 51% to the increase in FVC in the reserve, respectively, and the contribution of human activities was greater than that of climate variability. The warming and humidification phenomena in the reserve were obvious. However, precipitation was the dominant factor affecting the dynamic changes in FVC. This study improves our understanding of the response of vegetation dynamics to the climate and human activities in the QMNNR.