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Summary: Astronomy & Astrophysics manuscript no. Ban12242 c ESO 2009
June 18, 2009
LETTER TO THE EDITOR
Signatures of Alfv´en waves in the polar coronal holes as seen by
EIS/Hinode
D. Banerjee1, D. P´erez-Su´arez2, and J.G. Doyle2
1
Indian Institute of Astrophysics, Bangalore 560034, India
2
Armagh Observatory, College Hill, Armagh BT61 9DG, N.Ireland
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 Alfv´en 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 &
195.119 Å and Fe XIII 203.82 Å & 202.04 Å .
Results. For the polar region, the line width data show that the nonthermal line-of-sight velocity increases from 26 km s-1
at 10
above the limb to 42 km s-1
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