Search Publications
Rayleigh-Taylor and Richtmyer-Meshkov instabilities: A journey through scales
Zhou, Ye; Williams, Robin J. R.; Ramaprabhu, Praveen +9 more
Hydrodynamic instabilities such as Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities usually appear in conjunction with the Kelvin-Helmholtz (KH) instability and are found in many natural phenomena and engineering applications. They frequently result in turbulent mixing, which has a major impact on the overall flow development and othe…
Slow-Mode Magnetoacoustic Waves in Coronal Loops
Reale, Fabio; Srivastava, Abhishek K.; Ofman, Leon +3 more
Rapidly decaying long-period oscillations often occur in hot coronal loops of active regions associated with small (or micro-) flares. This kind of wave activity was first discovered with the SOHO/SUMER spectrometer from Doppler velocity measurements of hot emission lines, thus also often called "SUMER" oscillations. They were mainly interpreted a…
Solar force-free magnetic fields
Wiegelmann, Thomas; Sakurai, Takashi
The structure and dynamics of the solar corona is dominated by the magnetic field. In most areas in the corona magnetic forces are so dominant that all non-magnetic forces such as plasma pressure gradients and gravity can be neglected in the lowest order. This model assumption is called the force-free field assumption, as the Lorentz force vanishe…
Reconnection nanojets in the solar corona
Antolin, Patrick; Pagano, Paolo; Testa, Paola +2 more
The solar corona is shaped and mysteriously heated to millions of degrees by the Sun's magnetic field. It has long been hypothesized that the heating results from a myriad of tiny magnetic energy outbursts called nanoflares, driven by the fundamental process of magnetic reconnection. Misaligned magnetic field lines can break and reconnect, produci…
Solar oxygen abundance
Carlsson, Mats; Reiners, Ansgar; Bergemann, Maria +10 more
Motivated by the controversy over the surface metallicity of the Sun, we present a re-analysis of the solar photospheric oxygen (O) abundance. New atomic models of O and Ni are used to perform non-local thermodynamic equilibrium (NLTE) calculations with 1D hydrostatic (MARCS) and 3D hydrodynamical (Stagger and Bifrost) models. The Bifrost 3D MHD s…
A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)
Reeves, Katharine K.; Polito, Vanessa; Liu, Wei +11 more
The Interface Region Imaging Spectrograph (IRIS) has been obtaining near- and far-ultraviolet images and spectra of the solar atmosphere since July 2013. IRIS is the highest resolution observatory to provide seamless coverage of spectra and images from the photosphere into the low corona. The unique combination of near- and far-ultraviolet spectra…
First Fermi-LAT Solar Flare Catalog
Troja, E.; Orlando, E.; Ajello, M. +82 more
We present the first Fermi-Large Area Telescope (LAT) solar flare catalog covering the 24th solar cycle. This catalog contains 45 Fermi-LAT solar flares (FLSFs) with emission in the γ-ray energy band (30 MeV-10 GeV) detected with a significance of ≥5σ over the years 2010-2018. A subsample containing 37 of these flares exhibits delayed emission bey…
Mapping solar magnetic fields from the photosphere to the base of the corona
Hara, Hirohisa; De Pontieu, Bart; Carlsson, Mats +25 more
Routine ultraviolet imaging of the Sun's upper atmosphere shows the spectacular manifestation of solar activity; yet we remain blind to its main driver, the magnetic field. Here we report unprecedented spectropolarimetric observations of an active region plage and its surrounding enhanced network, showing circular polarization in ultraviolet (Mg I…
Upflows in the Upper Solar Atmosphere
Tian, Hui; Brooks, David H.; Baker, Deborah +2 more
Spectroscopic observations at extreme- and far-ultraviolet wavelengths have revealed systematic upflows in the solar transition region and corona. These upflows are best seen in the network structures of the quiet Sun and coronal holes, boundaries of active regions, and dimming regions associated with coronal mass ejections. They have been intensi…
Coronal Hole Detection and Open Magnetic Flux
Temmer, Manuela; Vršnak, Bojan; Pinto, Rui F. +14 more
Many scientists use coronal hole (CH) detections to infer open magnetic flux. Detection techniques differ in the areas that they assign as open, and may obtain different values for the open magnetic flux. We characterize the uncertainties of these methods, by applying six different detection methods to deduce the area and open flux of a near-disk …