THE ORIGIN OF TYPE I SPICULE OSCILLATIONS

D. B. Jess*, D. J. Pascoe, D. J. Christian, M. Mathioudakis, P. H. Keys, F. P. Keenan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

56 Citations (Scopus)

Abstract

We use images of high spatial and temporal resolution, obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope, to reveal how the generation of transverse waves in Type I spicules is a direct result of longitudinal oscillations occurring in the photosphere. Here we show how pressure oscillations, with periodicities in the range of 130-440 s, manifest in small-scale photospheric magnetic bright points, and generate kink waves in the Sun's outer atmosphere with transverse velocities approaching the local sound speed. Through comparison of our observations with advanced two-dimensional magnetohydrodynamic simulations, we provide evidence for how magnetoacoustic oscillations, generated at the solar surface, funnel upward along Type I spicule structures, before undergoing longitudinal-to-transverse mode conversion into waves at twice the initial driving frequency. The resulting kink modes are visible in chromospheric plasma, with periodicities of 65-220 s, and amplitudes often exceeding 400 km. A sausage mode oscillation also arises as a consequence of the photospheric driver, which is visible in both simulated and observational time series. We conclude that the mode conversion and period modification is a direct consequence of the 90 degrees phase shift encompassing opposite sides of the photospheric driver. The chromospheric energy flux of these waves are estimated to be approximate to 3 x 10(5) W m(-2), which indicates that they are sufficiently energetic to accelerate the solar wind and heat the localized corona to its multi-million degree temperatures.

Original languageEnglish
Article number5
Number of pages6
JournalAstrophysical Journal Letters
Volume744
Issue number1
DOIs
Publication statusPublished - 1 Jan 2012

Keywords

  • magnetohydrodynamics (MHD)
  • methods: numerical
  • Sun: atmosphere
  • Sun: chromosphere
  • Sun: oscillations
  • Sun: photosphere
  • MAGNETIC BRIGHT POINTS
  • ALFVEN WAVES
  • SOLAR ATMOSPHERE
  • CHROMOSPHERIC NETWORK
  • FLUX TUBES
  • MHD WAVES
  • QUIET SUN
  • CORONA
  • SUFFICIENT
  • PLASMA

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