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On the generation of solar spicules and Alfvénic waves

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Science  23 Jun 2017:
Vol. 356, Issue 6344, pp. 1269-1272
DOI: 10.1126/science.aah5412
  • Fig. 1 Spicule-like features (indicated by arrows) occur in our radiative MHD simulations.

    They appear as dense, cool intrusions in the hot corona, originating from the boundaries of the strong magnetic regions. (A) Temperature and (B) density maps are shown on a logarithmic color map with white magnetic field lines (A) and black contours where plasma β = 1 (B). t, time.

  • Fig. 2 Spicules form when strong magnetic tension is diffused into the upper chromosphere, where its release drives strong flows, heating, and Alfvénic waves.

    (A to P) A time series is shown of temperature, absolute velocity (|u|), ambipolar diffusion (ηamb), and current perpendicular to the plane (Jy). The thick white contour is at 105 K in (E) to (P). The region of strong tension is illustrated in (A) to (C) with white magnetic field lines. The fully formed spicule is shown in the rightmost panels. White arrows in (I) to (L) show ambipolar velocities leading to upward diffusion of the high-tension region. Strong ambipolar diffusion in the expanding emerging flux bubble at t = 1280 s concentrates the perpendicular current at the edges of the bubble, amplifying the tension. Pink contours in (G) show locations of a strong plasma pressure gradient (driving spicular flows upward) resulting from the release of magnetic tension (pink arrow).

  • Fig. 3 Heating of spicules from dissipation of electrical currents through ambipolar diffusion.

    (A to X) Time series of maps of temperature, absolute velocity, density, and Joule heating per particle from ambipolar diffusion (where Qjamb is Joule heating per volume and ρ is density). The median temperature (F), maximum velocity (L), median density (R), and median Joule heating per particle from ambipolar diffusion (X) within the spicule (<105 K) are shown as a function of time and height. Magnetic field lines are in white in (A) to (E), and the thick white contour is at 105 K in the three bottom rows. The rightmost column includes a thin contour at 8 × 103 K.

  • Fig. 4 Synthetic observations of a simulated spicule compared with observations from the Swedish 1-m Solar Telescope (SST) and the Interface Region Imaging Spectrograph (IRIS).

    (A to D) Wavelength-space plots of synthetic observations of Caii 8542 Å (middle chromosphere), Mgii h 2803 Å (upper chromosphere), Siiv 1403 Å (transition region), and Feix 171 Å (corona). The spicular signal appears as a blueward excursion around 3 to 6 arc sec (red arrows). The signals are offset spatially because the spicule is inclined from the vertical. (E to H) A disk observation of a spicule (or RBE) in Caii 8542 Å (SST), Mgii h 2803 Å (IRIS), and Siiv 1403 Å (IRIS), and a map of the blue wing (–41 km s−1) of Hα 6563 Å (SST). The white dotted line in (H) indicates the location of the IRIS slit. The spatial range in (A) to (D) corresponds to the region shown in Fig. 3 at t = 929 s.

Supplementary Materials

  • On the generation of solar spicules and Alfvénic waves

    J. Martínez-Sykora, B. De Pontieu, V. H. Hansteen, L. Rouppe van der Voort, M. Carlsson, T. M. D. Pereira

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Supplementary Text
    • Figs. S1 to S6
    • Table S1
    • Captions for Movies S1 to S5
    • References

    Images, Video, and Other Media

    Movie S1
    The large-scale simulation reveals distinct regions where different processes occur. Spicule-like features naturally occur in these radiative MHD simulations. They appear as dense, relatively cool intrusions in the hot corona, originating from the boundaries of the strong magnetic field regions. The simulated spicules reach heights up to 10 Mm. Temperature (A) and density maps (B) are shown in a logarithmic scale. Magnetic field lines are drawn in white on the top panel and the height at which plasma β=1 is the thick red contour (A) and black contour (B).
    Movie S2
    Spicules form when regions of strong magnetic tension, generated at the solar surface from the interaction between vertical magnetic flux concentrations and horizontal fields, are diffused into the low plasma β upper chromospheric region. This results in a violent release of the tension which drives strong flows and heating, and generates Alfvén waves. Time evolution of maps of temperature, ambipolar diffusion, absolute velocity and current perpendicular to the plane maps are shown in panels A-D. The temperature contour at 105 K is the thick white contour. Magnetic field lines are drawn in white and they are advected taking into account the advection of the fluid and the ambipolar velocity. These lines are highlighting the region of strong magnetic tension. Strong ambipolar diffusion (t=1280s) in the expanding emerging flux bubble concentrates the perpendicular current at the edges of the bubble, amplifying the tension
    Movie S3
    Heating of spicules from dissipation of electrical currents through ambipolar diffusion. The modeled spicule undergoes vigorous heating and reaches temperatures above 104 K within two minutes. The total lifetime (as measured at higher temperatures) is ~8 min, which is in agreement with observations. Time series of maps are shown for temperature (A), absolute velocity (C), density (E) and Joule heating per particle due to the ambipolar diffusion (G). The right column shows the median temperature (B), maximum velocity (D), median density (F) and median Joule heating per particle due to the ambipolar diffusion (H) within the spicule, i.e., over temperatures lower than 105 K, as a function of height and time. Magnetic field lines are drawn in white (A). Temperature contours at 105 K are shown in the three bottom rows. The right column also includes a temperature contour at 8x103 K. The red dashed lines in panel C shows the region where we calculated the medians or maximums for the right panels.
    Movie S4
    Hot loops (up to 2 MK) are formed in association with spicules. This can be seen with the temperature maps of the simulation with ambipolar diffusion and temperature contour at 105 K shown in this movie.
    Movie S5
    Transverse waves propagating parallel to the photosphere drive supersonic flows along the bent field lines. Time series of maps of energy flux of transverse waves with magnetic field lines in white are shown in panel A, absolute velocity parallel and perpendicular to the magnetic field in panels B-C respectively. The top contours correspond to a 105 K temperature and the bottom contours correspond to plasma beta unity. Magnetic field lines are drawn in white on panel A.

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