Ultra-high-resolution observations of persistent null-point reconnection in the solar corona.

Magnetic reconnection is a key mechanism involved in solar eruptions and is also a prime possibility to heat the low corona to millions of degrees. Here, we present ultra-high-resolution extreme ultraviolet observations of persistent null-point reconnection in the corona at a scale of about 390 km over one hour observations of the Extreme-Ultraviolet Imager on board Solar Orbiter spacecraft. The observations show formation of a null-point configuration above a minor positive polarity embedded within a region of dominant negative polarity near a sunspot. The gentle phase of the persistent null-point reconnection is evidenced by sustained point-like high-temperature plasma (about 10 MK) near the null-point and constant outflow blobs not only along the outer spine but also along the fan surface. The blobs appear at a higher frequency than previously observed with an average velocity of about 80 km s-1 and life-times of about 40 s. The null-point reconnection also occurs explosively but only for 4 minutes, its coupling with a mini-filament eruption generates a spiral jet. These results suggest that magnetic reconnection, at previously unresolved scales, proceeds continually in a gentle and/or explosive way to persistently transfer mass and energy to the overlying corona.

The role of non-axisymmetry of magnetic flux rope in constraining solar eruptions.

Whether a solar eruption is successful or failed depends on the competition between different components of the Lorentz force exerting on the flux rope that drives the eruption. The present models only consider the strapping force generated by the background magnetic field perpendicular to the flux rope and the tension force generated by the field along the flux rope. Using the observed magnetic field on the photosphere as a time-matching bottom boundary, we perform a data-driven magnetohydrodynamic simulation for the 30 January 2015 confined eruption and successfully reproduce the observed solar flare without a coronal mass ejection. Here we show a Lorentz force component, resulting from the radial magnetic field or the non-axisymmetry of the flux rope, which can essentially constrain the eruption. Our finding contributes to the solar eruption model and presents the necessity of considering the topological structure of a flux rope when studying its eruption behaviour.

[Analysis of 15 cases of avian influenza virus (H7N9) infection].

Objective: To describe the clinical, chest imaging, pathological manifestations and therapeutic experience of human infection with A/H7N9 virus. Methods: The features of 15 laboratory-confirmed cases of human infection with A/H7N9 virus in Taizhou, Jiangsu Province were retrospectively analyzed. Results: The 15 patients with confirmed viral pneumonia included 12 males and 3 females, with a median age of 61 years(ranging from 33 to 81 years). Twelve patients had a history of exposure to the poultry trading places, or direct contact with ill/dead avian, while 3 patients denied exposure or contact. The most common initial symptoms were fever, coughing, and respiratory distress. The illness progressed rapidly to acute respiratory distress syndrome (ARDS). Lab tests showed normal (8 cases) or decreased (7 cases)white blood cell count , decreased (13 cases) lymphocyte count and proportion , increased creatine kinase (CK, 12 cases) and lactate dehydrogenase (LDH, 15 cases), and respiratory failure (13 cases). Chest radiographic examination showed that the most common features were inflammatory infiltration in the lung, with partial consolidation. The average time of the diagnosis with influenza viral nucleic acid and onset of an oral anti-influenza drug were 7.1 days and 6.5 days. All patients were treated by antiviral drugs (oral oseltamivir 150 mg q12 h and/or intravenous paramivir 600 mg qd), with mechanical ventilation in 9 cases, glucocorticoid therapy in 5 cases (intravenous methylprednisolone in 3 and dexamethasone in 2 patients), extracorporeal membrane oxygenation (ECMO) therapy in 2 cases, continuous renal replacement therapy (CRRT) in 6 cases, and artificial liver therapy in 1 case. The pulmonary pathology was observed from post-mortem biopsy for 2 fatal cases. Patient 1 had diffuse alveolar damage with inflammatory exudation, hyaline membrane formation, and cellular infiltration. Patient 2 had widened alveolar septum, lymphocyte and monocyte cell infiltration in the alveolar septa, and interstitial fibrous proliferation. Nine patients were discharged, and 6 died. Conclusions: Patients with influenza A/H7N9 virus mostly presented with fever, cough, and were prone to progression to viral pneumonia. Once acute respiratory distress and important organ dysfunction occurred, the fatality rate was higher. Early diagnosis and rational treatment were critical for better outcomes.

Period Increase and Amplitude Distribution of Kink Oscillation of Coronal Loop.

Coronal loops exist ubiquitously in the solar atmosphere. These loops puzzle astronomers over half a century. Solar magneto-seismology (SMS) provides a unique way to constrain the physical parameters of coronal loops. Here, we study the evolution of oscillations of a coronal loop observed by the Atmospheric Imaging Assembly (AIA). We measure geometric and physical parameters of the loop oscillations. In particular, we find that the mean period of the oscillations increased from 1048 to 1264 s during three oscillatory cycles. We employ the differential emission measure method and apply the tools of SMS. The evolution of densities inside and outside the loop is analyzed. We found that an increase of density inside the loop and decrease of the magnetic field strength along the loop are the main reasons for the increase in the period during the oscillations. Besides, we also found that the amplitude profile of the loop is different from a profile would it be a homogeneous loop. It is proposed that the distribution of magnetic strength along the loop rather than density stratification is responsible for this deviation. The variation in period and distribution of amplitude provide, in terms of SMS, a new and unprecedented insight into coronal loop diagnostics.

Observationally quantified reconnection providing a viable mechanism for active region coronal heating.

The heating of the Sun's corona has been explained by several different mechanisms including wave dissipation and magnetic reconnection. While both have been shown capable of supplying the requisite power, neither has been used in a quantitative model of observations fed by measured inputs. Here we show that impulsive reconnection is capable of producing an active region corona agreeing both qualitatively and quantitatively with extreme-ultraviolet observations. We calculate the heating power proportional to the velocity difference between magnetic footpoints and the photospheric plasma, called the non-ideal velocity. The length scale of flux elements reconnected in the corona is found to be around 160 km. The differential emission measure of the model corona agrees with that derived using multi-wavelength images. Synthesized extreme-ultraviolet images resemble observations both in their loop-dominated appearance and their intensity histograms. This work provides compelling evidence that impulsive reconnection events are a viable mechanism for heating the corona.

A circular white-light flare with impulsive and gradual white-light kernels.

White-light flares are the flares with emissions visible in the optical continuum. They are thought to be rare and pose the most stringent requirements in energy transport and heating in the lower atmosphere. Here we present a nearly circular white-light flare on 10 March 2015 that was well observed by the Optical and Near-infrared Solar Eruption Tracer and Solar Dynamics Observatory. In this flare, there appear simultaneously both impulsive and gradual white-light kernels. The generally accepted thick-target model would be responsible for the impulsive kernels but not sufficient to interpret the gradual kernels. Some other mechanisms including soft X-ray backwarming or downward-propagating Alfvén waves, acting jointly with electron beam bombardment, provide a possible interpretation. However, the origin of this kind of white-light kernel is still an open question that induces more observations and researches in the future to decipher it.

Extreme ultraviolet imaging of three-dimensional magnetic reconnection in a solar eruption.

Magnetic reconnection, a change of magnetic field connectivity, is a fundamental physical process in which magnetic energy is released explosively, and it is responsible for various eruptive phenomena in the universe. However, this process is difficult to observe directly. Here, the magnetic topology associated with a solar reconnection event is studied in three dimensions using the combined perspectives of two spacecraft. The sequence of extreme ultraviolet images clearly shows that two groups of oppositely directed and non-coplanar magnetic loops gradually approach each other, forming a separator or quasi-separator and then reconnecting. The plasma near the reconnection site is subsequently heated from ∼1 to ≥5 MK. Shortly afterwards, warm flare loops (∼3 MK) appear underneath the hot plasma. Other observational signatures of reconnection, including plasma inflows and downflows, are unambiguously revealed and quantitatively measured. These observations provide direct evidence of magnetic reconnection in a three-dimensional configuration and reveal its origin.