Plumes are one of the most representative dynamic features observed in prominences and play a key role in mass and magnetic transport within them. However, their physical nature and triggering processes remain actively debated. Based on limb Hα observations from the New Vacuum Solar Telescope (NVST) during 2013–2025, we statistically investigated 34 plumes with clear and complete evolutions by developing an automated image-processing pipeline. It is revealed that plume lifetimes mainly range from 300 s to 700 s, with vertical displacements between 3–7 Mm. The mean widths and velocities are concentrated in the range of 0.5–1.5 Mm and 10–20 km s^-1, respectively. Besides wide distribution ranges, plume parameters exhibit irregular evolution fluctuations, indicating that the formation and evolution of various plumes may exhibit different physical patterns. Correlation analysis among the parameters further reveals that: (1) Positive correlations were found among lifetime, vertical displacement, and mean width, indicating an intrinsic coupling between the temporal and spatial scales of plumes. (2) Trajectory curvature is negatively correlated with lifetime, vertical displacement, and velocity. Accelerating and width-contracting plumes typically have lower curvature, suggesting that curvature may reflect environmental influences and the stability of plumes. (3) Plumes with higher initial velocities were more likely to be accompanied by precursor brightening, suggesting that these plumes may be triggered by magnetic reconnection. Furthermore, we infer that some plumes in non-bubble regions may be inherently driven by mini-filament eruptions. These results establish a statistical framework for prominence plumes and reveal diversity in their dynamical evolution and triggering mechanisms.

Accurate calibration of the Sky Brightness Monitors (SBMs) is crucial for reliable astronomical site evaluation and solar coronal observation planning. However, the measurement accuracy and the mutual consistency between SBMs developed by different teams remain unverified, limiting the integration of data sets from multiple instruments. In this study, we present a comprehensive cross calibration of the SBMs respectively developed by the Chinese Giant Solar Telescope (CGST) team and the Advanced Technology Solar Telescope (ATST, previous name for the 4 m DKIST) team, based on three calibration campaigns conducted at Zhaotong, Ali and Daocheng sites. By overcoming the harsh conditions brought by high-altitude field observation, we used the two sets of SBM equipments to observe simultaneously at these sites, and obtained the data profile of each site for a whole day, enabling a robust analysis for the cross-calibration of the SBMs. The results show that the efficacy of the calibration process is highly dependent on site-specific atmospheric stability conditions, with Daocheng providing the most stable and reliable calibration environment. The analysis further distinguishes site-dependent atmospheric effects from instrument-intrinsic calibration offsets, showing that the latter persist under stable observing conditions and can be robustly quantified at Daocheng. Based on the complete measurement records at Daocheng, the final calibration values at 530 nm are determined to be -0.92 & times; 10(-6)I(circle dot) (I-circle dot: solar disk-center brightness) and -0.515 & times; 10(-6)I(circle dot)/airmass (airmass: air mass along the line of sight for observation) for the two instruments, i.e., the measurement value of CGST SBM is only 1 & times; 10(-6)I(circle dot )less than that of ATST SBM equipment, which is completely within the measurement error range of the equipment itself. The high consistency achieved validates the integration of CGST SBM data sets into ATST-related analyses and confirms both instruments' suitability for routine sky brightness monitoring at optimal sites.

Understanding the filament rising process is crucial for unveiling the triggering mechanisms of coronal mass ejections and forecasting space weather. In this paper, we present a detailed study of the filament initial eruption under a fan–spine structure. It was found that the filament underwent two distinct acceleration stages corresponding to class M1.0 and M4.6 flare events. The first acceleration stage commenced with the filament splitting, after which the upper portion was subsequently heated, being a hot channel, and slowly rose at an average speed of 22 km s ^−1 . A set of hot reverse C-shaped loops appeared repeatedly during the filament splitting, and a hook structure was recognized at this phase, suggesting ongoing growth of the magnetic flux rope (MFR). When it reached a certain altitude, the hot channel appeared to get into a quasi-static phase with its upper edge seriously decelerated and its lower edge expanding downward. Approximately 30 minutes later, as a distinct annular ribbon appeared outside the hook structure, the hot channel rose again at a velocity of over 50 km s ^−1 accompanied by rapidly drifting footpoints and experienced a second acceleration stage with its axial flux increased to 1.1 × 10 ^21 Mx. It is deduced that the filament initial eruption under a magnetic dome possesses multiple kinetic processes. We suggest that the magnetic reconnection taking place within and beneath the filament continues to trigger the growth of preeruptive MFR and the first acceleration, when the magnetic reconnection above the filament plays a key role in the second acceleration.

The Lyot filter, a fundamental element of the Yunnan Observatories Coronagraph Green-line Imaging System (YOGIS) at Lijiang Observatory, utilizes a Liquid Crystal Variable Retarder (LCVR) for swift electrical modulation. This filter allows for precise observations of the coronal green line (Fe XIV, central wavelength 5303 Å) with a narrow full-width at half-maximum (FWHM) of 1 Å and enables rapid adjustment of the transmission band wavelength. This feature aids in capturing the sky background intensity around the green line and images of two line wings (offset by ±0.45 Å from the central wavelength), crucial for determining the green line’s Doppler shift. By employing sky background subtraction and processing line wing images, an improved signal-to-noise ratio (SNR) in coronal green line images is achieved. The YOGIS Lyot filter, an enhancement of the NOrikura Green-line Imaging System (NOGIS) filter, operates at a wavelength of 5303 Å, offers a wavelength tuning range of ±2 Å, and tunes within <60 ms. This study elucidates the filter’s design principles, outlines essential calibration procedures, and validates its performance through on-site observations using the YOGIS.

High-precision ground-based observations of the inner corona (1.05-2.0 R circle dot) are fundamentally constrained by instrumental stray light, particularly the additive background from dynamic dust accumulation on the objective lens. To address this issue, we propose a correction method for the Spectral Imaging Coronagraph (SICG) based on dual-path real-time monitoring and forward physical modeling. By simultaneously imaging the objective lens surface, we obtain deterministic prior information on dust distribution. We construct a physical point-spread function using optical defocus parameters and reconstruct the nonuniform scattering background via convolution. Model parameters are retrieved through data-driven inversion constrained by polar coronal holes. The method demonstrates excellent robustness under varying contamination conditions. After correction, the rms noise in the polar background is reduced by approximately 67% on average, and the signal-to-background ratio improves by a factor of up to 3.7 under heavy contamination conditions. Comparisons with space-based Solar Dynamics Observatory/Atmospheric Imaging Assembly observations indicate that the corrected images recover the morphological structures of streamers with high fidelity. Further radial intensity analysis reveals that the correction process successfully restores the hydrostatic exponential decay characteristic of inner coronal radiation. The fitted decay coefficient corresponds to a plasma temperature of approximately 2.0 MK, consistent with the characteristic formation temperature of the Fe xiv 530.3 nm line. These results demonstrate that the method effectively eliminates the dominant systematic bias in ground-based observations, providing a reliable data foundation for high-precision coronal thermodynamic and dynamic research with the SICG.

As a core ground-based coronal observation facility in the low-latitude and high-altitude regions of China, the Lijiang Coronagraph takes advantage of the natural endowments of the Lijiang Astronomical Observation Station, such as an altitude of 3200 m and low atmospheric turbulence. It has gone through a complete development process from introduction through Chinese–Japanese cooperation to independent innovation and iteration. This paper systematically summarizes the core technological innovation achievements of this facility, including the upgrade of the automatic operating system, the integration of the dual-band observation system, the stray light suppression technology based on the image difference method before and after cleaning, and the high-precision image calibration and registration technology. These innovations have significantly improved observation efficiency and data quality, laying a solid foundation for high-quality observations. At the scientific research level, the observation data reveal that 1.1 R⊙ (solar radius) is a highly correlated region between coronal green line brightness and magnetic field intensity. This study also confirms a strong correlation between the coronal green line and the SDO/AIA 211 Å extreme ultraviolet band (correlation coefficient: 0.89–0.99), which can support the research on early warning of Coronal Mass Ejections (CMEs). These achievements provide key data support for the verification of coronal heating mechanisms and the exploration of the origin of the slow solar wind. The technical experience accumulated from the Lijiang Coronagraph has not only laid a solid foundation for the research and development of China’s next-generation large-aperture coronagraphs, but also facilitated and accelerated substantial progress in China’s technical capabilities for low coronal observation, enabling the country to establish internationally parallel competitive capabilities in this field. This system has also become an important part of the global coronal observation network.

Abstract Quantifying the terrestrial response of solar variability across the 11-year Schwabe cycle remains an open challenge in solar-terrestrial physics, due to the dominance of anthropogenic warming signals and the limitations of conventional statistical approaches. We present a Physics-Informed Neural Network (PINN) constrained by the zero-dimensional energy balance equation C dT /dt = αS(t) + γ CO2(t) − βT (t), trained on 1488 months of detrended global surface temperature anomalies (1900--2023). By jointly minimising data misfit and the energy balance residual, the PINN learns forcing parameters directly from observations while remaining physically constrained. The model achieves R^2 = 0.844 +/- 0.002 on held-out test data, compared to R^2 = 0.178 for conventional multiple linear regression (MLR) applied to the same detrended dataset, demonstrating that physics-constrained temporal modelling provides both the predictive skill and the parameter stability that instantaneous regression and unconstrained temporal models cannot simultaneously achieve. The found learned solar sensitivity α = 0.088 +/- 0.001 is physically consistent with published estimates of solar climate sensitivity. Spectral analysis of the model-isolated solar component independently recovers the Schwabe solar cycle at ~10.2 yr without prior specification of the expected period. The solar forcing share expressed as α/(α + γ) = 15.5 +/- 0.3%, stable across five independent training realisations, quantifies the solar contribution to total modelled radiative forcing sensitivity in the detrended residual record. Applying the same framework across spatial scales reveals systematic degradation of predictive skill from global to urban station scale (R^2 = 0.844 to R^2 ~0), while the solar share remains physically consistent (14.7--18.5 +/- 0.5%) across all converging analyses. A historical Riyadh-city station independently recovers a dominant spectral peak consistent with the mean Schwabe period (11.0 +/- 0.5 yr) with R^2 = 0.577 +/- 0.060, confirming the presence of the solar signal in pre‑urban Arabian Peninsula desert temperature records. The scale‑dependent degradation in model performance demonstrates that anthropogenic urban processes may elevate the effective thermal noise floor beyond the detectable amplitude of the solar signal, with implications for solar–terrestrial studies relying on urban ground‑station datasets. An ablation study confirms that the energy balance physics constraint --- rather than the LSTM temporal memory alone --- is the primary driver of parameter stability and interpretability. Removing this constraint destabilizes the solar attribution from 15.3 +/- 0.6% to 62 +/- 32% across training seeds.

This study presents a comprehensive analysis of atmospheric parameters at the Daocheng site (100 degrees 05' E, 29 degrees 08' N) in China, using the ERA5 reanalysis data spanning 2014-2024. By implementing a physical parametrization scheme, we derive the vertical profiles of temperature, wind speed and optical turbulence strength, characterized by the refractive index structure constant C-n(2)(h). Our analysis reveals exceptional atmospheric stability, characterized by minimal tropopause height variations (range: 17.06-17.81 km; annual amplitude < 0.74 km) and favourable summer conditions, with median 200 hPa wind speeds (V-200) remaining below 20 m s(-1) during June-September. The C-n(2)( h ) profile decreases monotonically from the surface to approximately 11 km, followed by a pronounced peak near 17 km that is strongly correlated with the local thermal structure. The derived optical turbulence parameters demonstrate excellent median seeing conditions (epsilon = 0.72 arcsec), with 25 per cent of values better than 0.48 arcsec, along with key parameters including atmospheric coherence length (r(0) = 14.07 cm), isoplanatic angle (theta(0) = 0.89 arcsec), and wavefront coherence time (tau(0) = 2.21 ms). The atmospheric coherence length consistently exceeds 20 cm during summer months, significantly outperforming spring-winter transitions. Based on this analysis, we develop an integrated forecasting framework combining ARIMA and Holt-Winters methodologies to predict the excellent seeing conditions for 2025. Time series analysis confirms a robust seasonal pattern, quantified by a seasonal intensity coefficient of 0.771. This work provides systematic estimation and forecasting of atmospheric turbulence parameters at the Daocheng site, establishing crucial scientific foundations for atmospheric characterization, adaptive optics system design, and strategic planning of current and future telescope facilities.

The solar corona has an extremely low density, and its brightness is only about one millionth of that of the photosphere. High-dynamic-range imaging of its faint structure is therefore essential for studying coronal heating, coronal mass ejections, and space weather. Quantitative coronagraph imaging requires flat-field measurement and calibration, which underpin intensity calibration, small-scale feature detection, and long-term cyclic analysis. This paper analyzes the coronagraph imaging chain (baffle–optical system–detector) and the origins of flat-field errors, including optical aberrations, stray light, and pixel-response non-uniformity, and summarizes the resulting calibration requirements of next-generation coronagraphs. On this basis, ground-based and space-based flat-fielding methods are systematically reviewed: the ground-based methods include integrating-sphere uniform light sources, opal glass/diffuser plates, clear-sky and thin-cloud backgrounds, and solar disk scanning, while the space-based methods include internal light sources and diffuser plates, attitude-roll and off-corona offset observations, and multi-phase statistical self-consistent flat-fielding. Their accuracy, resource cost, and applicability are compared. The review shows that no single method is simultaneously high-precision, easy to update, and engineer-friendly; a hierarchical, multi-method calibration framework is therefore recommended. Finally, a new method is proposed in which lithographically generated structured light fields, combined with Fourier optics and machine learning inversion, are used to estimate the pixel-response function. Preliminary experiments show that this method achieves a lower residual error than the integrating-sphere and opal glass methods, providing a high-precision reference for future wide-band, high-resolution coronagraph calibration.

Understanding the link between solar parameters and their influence on green line emissions would help unravel the complexities of eruptive phenomena within the solar corona. This study explores the intricate relationship between green line emissions and various solar indicators, including flares, F10.7 cm flux, and sunspot numbers. Utilizing data from both ground-based and space-based sources spanning from 1996 to 2024, covering solar cycles 23 to 25, the investigation employs the multitaper and cross-correlation analyses. The study reveals distinct behaviors and contributions to green line emissions at low and high latitudes. The F10.7 cm radio flux exhibits zero lag with green line emissions, indicating that both are contemporaneously influenced by solar activity, as shown by their correlation with sunspot numbers. In contrast, B-, M-, and X-class flares typically act as precursors or aftermaths of such activity. C-class flares exhibit a pronounced positive correlation with the green line, causally linked to plasma dynamics, particularly at low latitudes. Sunspots, on the other hand, act as a leading and significant indicator of the green line with positive lag, preceding the emissions. The emissions are found to be an excellent indicator of solar activity, with an immediate response to the F10.7 cm flux and a delayed response to sunspot emergence. The differences in observed impacts could be attributed to the behavior of confined plasma within magnetic loops, influenced by factors such as solar magnetic configurations, differential rotation, and dynamo mechanisms. These factors collectively impact the global coronal structure and influence the green line across latitudes.

The solar corona is the primary driver of the solar storms and space weather.In order to routinely monitor the coronal activities,a dedicated solar telescope is essential,a coronagraph.However,the site conditions suitable for a ground-based coronagraph are rather critical and necessitate stringent site selection criteria.Among the numerous astronomical observatory site parameters,the sky background brightness of the day is recognized as a key parameter in evaluating the quality of a solar observatory for coronal observation before considering to install a coronagraph.To achieve optimal sky brightness observing condition,coronagraphs are usually installed on high mountains where the atmosphere is thin and the background scattered light effects from the sky are significantly reduced.Given the unique characteristics of the Tibetan Plateau,often referred to as the"Third Pole"of the Earth,a scientific assessment is crucial to evaluate its suitability as a potential location for the next-generation Chinese Giant Solar Telescope and large coronagraphs.Here,we report the first results of our measurements of the sky brightness at the Namco Lake location(30°45.0′N,90°40.0′E,4730 m above sea level,the highest large lake in the world),using a new Sky Brightness Monitor during the period 2013 August to December.The results show that the average value of the normalized(per airmass)sky brightness is as low as 13.84 μI⊙ for 530 nm.The excellent sky brightness conditions at the Namco Lake location demonstrate its high suitability for routine coronal observations.Therefore,the Namco site deserves attention for solar observations and we should continue to carry out in-depth monitoring and systematic study of multiple parameters in the future.

Seeing is a key factor affecting the image quality of astronomical observations and can be quantitatively described by the Fried parameter r0. The larger the r0 value (in unit of cm), the better the seeing conditions. Currently, daytime seeing measurements are primarily conducted using the Solar Differential Image Motion Monitor (SDIMM) or the spectral ratio method. In this work, we propose a neural network model for estimating daytime r0. The experimental results of the training set and the test set show that this model can currently estimate r0 with an accuracy exceeding 99%. Using this model, we estimate the r0 of the Huairou Solar Observing Station (HSOS) in 22 consecutive years from 1989 to 2010. The median r0 of HSOS in 22 consecutive years was around 2.5 cm, and the best seeing condition was in April and September of one year. This result confirmed the long-term stability of seeing conditions. In addition, we conducted an error analysis comparing the seeing measured by SDIMM and the results obtained by the spectral ratio method both under domeless and domed conditions. The results indicate a significant correlation between the SDIMM results and the spectral ratio method results, with first-order fitting coefficients of 2.2 and 2.9, respectively.

The sky brightness is an important parameter to evaluate the excellence of a coronal observatory, which directly determines whether the coronagraph can measure and monitor the coronal activity for a long time. The Sky Brightness Moniter (SBM) is a precision instrument for accurately measuring important atmospheric parameters such as the sky brightness, water vapor content, and atmospheric extinction. It is also an universal instrument for coronagraph site selection and an important equipment for solar site selection in western China. Before conducting statistical analysis on the accumulated data from Namco, this paper first performs an in-depth analysis using representative data from Namco and Lijiang. The aim is to preliminarily study and understand the characteristics of the sky brightness at the site based on the profiles of the representative data. Firstly, by considering the actual climatic characteristics and the normalized sky brightness, the paper gradually explains the different variations of the sky brightness throughout the day. Secondly, we establish an effective calculation method to measure and reveal the evolution characteristics of the sky brightness. The results show: 1) The sky brightness (green line, 530 nm) at the Lijiang station with an altitude of 3200 meters and the Namco site with an altitude of 4700 meters are both relatively good. The minimum values can reach the order of 10×10−6, ensuring the feasibility of regular corona observations. 2) The sky brightness at the Namco site and the Lijiang station evolves differently over time. The Lijiang station is not suitable for all-day observations, with morning conditions being far superior to those in the afternoon. In contrast, the Namco site has a longer observation time (from 9:00 AM to 4:00 PM), and its cooperation with the observation equipment of other stations can significantly improve the efficiency of space weather ground monitoring. The analysis results not only provides a sample analysis for subsequent statistics on the sky brightness at Namco but also demonstrates the expected characteristics of the sky brightness at Namco.

During solar storms, the polar cusp often exhibits electron populations with distinct velocity distributions, which may be associated with the two-stream instability. This study reveals the evolution of the two-stream instability associated with electron velocities and the interaction between the growth phase of the two-stream instability and the electrostatic solitary waves (ESWs). The results from particle-in-cell (PIC) simulations are compared with satellite observational data and computational outcomes. The potential risks associated with two-stream instability, including surface charge accumulation and communication system interference on spacecraft, are also explored. The findings show that, in the high-latitude polar cusp region, the interaction between the solar wind plasma propagating along magnetic field lines and the upward-moving ionospheric plasma could drive two-stream instability, leading to the formation of electron hole structures in phase space and triggering a bipolar distribution of ESWs. When the spatial magnetic field and wave vector meet specific conditions, the enhanced electron cyclotron motion could suppress the formation of two-stream instability and electron hole structures, leading to a reduction in the amplitude of the ESWs. The results offer valuable insights for a deeper understanding of the impact of solar storms on the polar cusp environment, as well as for monitoring electromagnetic environment and ensuring the stable operation of spacecraft.

A few ground-based solar coronagraphs have been installed in western China for observing the low-layer corona in recent years. However, determining the helioprojective coordinates for the coronagraphic data with high precision is an important but challenging step for further research with other multiwavelength data. In this paper, we propose an automatic coronal image registration method that combines local statistical correlation and feature point matching to achieve accurate registration between ground-based coronal green-line images and space-based 211 & Aring; images. Then, the accurate field of view information of the coronal green-line images can be derived, allowing the images to be mapped to the helioprojective Cartesian coordinates with an accuracy of no less than 0.'' 1 . This method has been extensively validated using 100 days of coronal data spanning an 11 yr period, demonstrating its broad applicability to ground-based coronagraphs equipped with green-line observations. It significantly enhances the scientific value of ground-based coronal data, enabling comprehensive studies of coronal transient activities and facilitating the joint analysis of data from multiple instruments. Additionally, it holds potential for future applications in improving the pointing accuracy of coronagraphs.

Moreton waves are widely regarded as the chromospheric counterpart of extreme ultraviolet waves propagating in the corona. However, direct observational evidence confirming their simultaneous propagation across multiple atmospheric layers—from the corona through the transition region to the chromosphere—has been lacking. In this study, we present comprehensive observational evidence of a 3D fast-mode wave propagating from the corona through the transition region into the chromosphere, exhibiting a gradual deceleration. Additionally, this wave interacts with three filaments (F1, F2, and F3) along its path, inducing oscillation with multiple amplitudes: filaments F1 and F2 exhibit simultaneous horizontal and vertical large-scale oscillations (∼20 km s ^−1 ), while filament F3 only exhibits vertical small-scale oscillation (∼4 km s ^−1 ). Interestingly, F1 displays a similar oscillation period of about 500 s in both horizontal and vertical directions, whereas F2 shows significantly different periods in these two dimensions (1100 and 750 s), and F3 exhibits only a vertical oscillation with a period of about 450 s. Based on this kinematic behavior, we propose that their oscillations were likely triggered by compression from the flanks of the dome-shaped wave front. We further estimate the magnetic fields of the filaments. The radial (axial) magnetic fields for F1 and F2 are estimated to be 14.9 G (28.6 G) and 9.9 G (18.6 G), respectively. For F3, we estimate its radial magnetic field to be 16.6 G.

A 50 mm balloon-borne white-light coronagraph (BBWLC) to observe white-light solar corona over the altitude range from 1.08 R-circle dot to 1.50 R-circle dot has recently been indigenously developed by Yunnan Observatories in collaboration with Shandong University (in Weihai) and Changchun Institute of Optics, Fine Mechanics and Physics, which will significantly improve the ability of China to detect and measure the inner corona. On 2022 October 4, its first scientific flight took place at the Dachaidan area in Qinghai province of China. We briefly describe the BBWLC mission including its optical design, mechanical structure, pointing system, the first flight and results associated with the data processing approach. Preliminary analysis of the data shows that BBWLC imaged the K-corona with three streamer structures on the west limb of the Sun. To further confirm the coronal signals obtained by BBWLC, comparisons were made with observations of the K-coronagraph of the High Altitude Observatory and the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. We conclude that BBWLC eventually observed the white-light corona in its first scientific flight.

Huairou Solar Observing Station of the National Astronomical Observatories of Chinese Academy of Sciences has been in operation since 1987. During its operation, successful observations of the solar vector magnetic field have been conducted. On the basis of the achievements at Huairou, we analyze the methods of observing the solar magnetic field, including discussions of the approximation of the transfer theory of the solar magnetic field in the atmosphere, wide field of view polarized observation, and some questions on the inversion of solar magnetic field data. We also present relevant challenges for further research.

In this article, we examine the morphological evolution and current distribution of the X9.3-class flare on 6 September 2017 that occurred in the active region (AR) 12673. We combine the high-resolution observations of the Atmospheric Imaging Assembly (AIA) and Helioseismic Magnetic Imager (HMI) instruments on board the Solar Dynamics Observatory. The vertical current intensity and the soft X-ray flux within the active region showed two peaks, corresponding, respectively, to the X2.2 and X9.3 flares on that day, while the latter constituted a more significant increase. A pair of conjugate current ribbons appeared at the same locations consistent with the two ribbons of the flare. These current ribbons underwent sustained and significant changes during the X9.3 flare eruption. In the early period of the flare, there was a substantial decrease in the area of the current ribbons, resulting in the emergence of a series of high-density small current islands. During the later phase, not only did the area of the currents rapidly increase, but also the flare kernels evolved into two flare bands along the sheared magnetic neutral line in the photosphere. The AIA 1600 Å and 304 Å images revealed that the two ribbons of the X9.3 flare formed from small bright kernels. It was also observed that the positions of the flare kernels closely matched those of the current islands. Based on the vertical current distribution and evolution near the highly sheared core field region during the X9.3 flare, we conclude that this flare eruption should be attributed to tether-cutting magnetic reconnection.