The Magnetic Response of the Solar Atmosphere to Umbral Flashes

S. J. Houston, D. B. Jess, A. Asensio Ramos, S. D. T. Grant, C. Beck, A. A. Norton, S. Krishna Prasad

Research output: Contribution to journalArticle

10 Citations (Scopus)
162 Downloads (Pure)

Abstract

Chromospheric observations of sunspot umbrae offer an exceptional view of magnetoacoustic shock phenomena and the impact they have on the surrounding magnetically dominated plasma. We employ simultaneous slit-based spectro-polarimetry and spectral imaging observations of the chromospheric He I 10830 Å and Ca II 8542 Å lines to examine fluctuations in the umbral magnetic field caused by the steepening of magnetoacoustic waves into umbral flashes. Following the application of modern inversion routines, we find evidence to support the scenario that umbral shock events cause expansion of the embedded magnetic field lines due to the increased adiabatic pressure. The large number statistics employed allow us to calculate the adiabatic index, γ = 1.12± 0.01, for chromospheric umbral locations. Examination of the vector magnetic field fluctuations perpendicular to the solar normal revealed changes up to ∼200 G at the locations of umbral flashes. Such transversal magnetic field fluctuations have not been described before. Through comparisons with nonlinear force-free field extrapolations, we find that the perturbations of the transverse field components are oriented in the same direction as the quiescent field geometries. This implies that magnetic field enhancements produced by umbral flashes are directed along the motion path of the developing shock, hence producing relatively small changes, up to a maximum of ∼8°, in the inclination and/or azimuthal directions of the magnetic field. Importantly, this work highlights that umbral flashes are able to modify the full vector magnetic field, with the detection of the weaker transverse magnetic field components made possible by high-resolution data combined with modern inversion routines.
Original languageEnglish
Article number28
Number of pages13
JournalThe Astrophysical Journal
Volume860
Issue number1
DOIs
Publication statusPublished - 07 Jun 2018

Keywords

  • shock waves
  • Sun: chromosphere
  • Sun: magnetic fields
  • Sun: oscillations
  • Sun: photosphere
  • sunspots

Fingerprint Dive into the research topics of 'The Magnetic Response of the Solar Atmosphere to Umbral Flashes'. Together they form a unique fingerprint.

Cite this