EDP Sciences
Free access
Issue
A&A
Volume 501, Number 3, July III 2009
Page(s) L15 - L18
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361/200912242
Published online 22 June 2009
A&A 501, L15-L18 (2009)
DOI: 10.1051/0004-6361/200912242

Letter

Signatures of Alfvén waves in the polar coronal holes as seen by EIS/Hinode

D. Banerjee1, D. Pérez-Suárez2, and J. G. Doyle2

1  Indian Institute of Astrophysics, Bangalore 560034, India
    e-mail: dipu@iiap.res.in
2  Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland

Received 1 April 2009 / Accepted 10 June 2009

Abstract
Context. We diagnose the properties of the plume and interplume regions in a polar coronal hole and the role of waves in the acceleration of the solar wind.
Aims. We attempt to detect whether Alfvén waves are present in the polar coronal holes through variations in EUV line widths.
Methods. Using spectral observations performed over a polar coronal hole region with the EIS spectrometer on Hinode, we study the variation in the line width and electron density as a function of height. We use the density sensitive line pairs of Fe XII 186.88 Å and 195.119 Å  and Fe XIII 203.82 Å and 202.04 Å.
Results. For the polar region, the line width data show that the nonthermal line-of-sight velocity increases from $26~{\rm km\,s}^{-1}$ at 10´´ above the limb to $42~{\rm km\,s}^{-1}$ some 150´´  (i.e. ~110 000 km) above the limb. The electron density shows a decrease from 3.3 $\times$ $10^9~{\rm cm}^{-3}$ to 1.9 $\times$ $10^8~{\rm cm}^{-3}$ over the same distance.
Conclusions. These results imply that the nonthermal velocity is inversely proportional to the quadratic root of the electron density, in excellent agreement with what is predicted for undamped radially propagating linear Alfvén waves. Our data provide signatures of Alfvén waves in the polar coronal hole regions, which could be important for the acceleration of the solar wind.


Key words: Sun: corona -- Sun: oscillations -- Sun: UV radiation -- line: profiles -- waves



© ESO 2009

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.