High-resolution observation of disk spicules. I. Evolution and kinematics of spicules in the enhanced network

Yoshinori Suematsu, Haimin Wang, Harold Zirin

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Abstract

We present measurements of a 75 minute sequence of CCD spicule observations at Hα -0.65 Å, line center, and +0.65 Å. The observations were made in a region of enhanced network near disk center, where most spicules are longer and tilted further from the vertical than those in truly quiet Sun. Images were reregistered with a correlation coefficient greater than 0.9. We identify the spicules as those elongated jets that radiate from elements of the magnetic network and are the main chromospheric features seen in the wing of Hα. Doppler images produced by red-blue subtraction show an upward radial velocity during the extension phase and a downward velocity during contraction for most spicules. Therefore, the spicules are truly moving up and down. There were a few plagelike cells filled with weak Hα emission, weak magnetic fields, and no spicules. We also found many multiple spicules. The data are presented with commentary on the accompanying videotape. We analyzed the data to understand the spicule lifetimes and trajectories. We found that the entire set of wavelengths and Dopplergrams was required to separate overlapping spicules. Seventy-six of the 96 spicules studied appear in complete upward and downward trajectories. The evidence on motions is not conclusive. Some proper motions are well represented by ballistic trajectories with initial injection velocity about 40 km s-1 for highly inclined spicules. The small decelerations would require the spicules to be tilted typically 60°-70° from the line of sight. Since limb observations favor tilts around 30°, our observations must favor spicules tilted greatly from the radial, as one finds in these enhanced field regions. The positive correlation of lifetimes with projected lengths supports this model. However, the Dopplergrams show that the entire spicule rises and falls as a whole, which favors a fountain jet or some acceleration in the flux tube. The downward trajectory may be slightly offset toward the network center from the upward path. Bright points often appear at the bases of spicules at Hα -0.65 Å, but during the peak extension or receding phase of the spicule rather than the beginning; therefore, the spicule is not a surgelike phenomenon (surges are usually initiated by Hα brightening or a subflare, invariably in a bipolar feature). Further, the magnetic elements, which match the Hα bright points exactly, show no change associated with the brightening. The geometry creates a problem for coronal heating models, as the spicule tops are at least 10″ displaced from the bright-point bases, but no such offset appears in the K line, for example. There is some evidence that the spicule is generated several hundred kilometers above the photosphere.

Original languageEnglish (US)
Pages (from-to)411-421
Number of pages11
JournalAstrophysical Journal
Volume450
Issue number1
DOIs
StatePublished - Sep 1 1995

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Sun: chromosphere
  • Sun: granulation
  • Videotapes

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