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Accelerating waves in polar coronal holes as seen by EIS and SUMER  

Girjesh R Gupta   Submitted: 2010-05-20 05:39

We present EIS/Hinode & SUMER/SoHO observations of propagating disturbances detected in coronal lines in inter-plume and plume regions of a polar coronal hole. The observation was carried out on 13th November 2007 as JOP196/HOP045 programme. The SUMER spectroscopic observation gives the information about the fluctuation in radiance and on both resolved (Doppler shift) and unresolved (Doppler width) line-of-sight velocities whereas EIS 40'' wide slot images detect fluctuations only in radiance but maximizes the probability of overlapping field of view between the two instruments. From distance-time radiance maps, we detect the presence of propagating waves in a polar inter-plume region with a period of 15 min to 20 min and a propagation speed increasing from (130 ? 14) km s-1 just above the limb, to (330 ? 140) km s-1 around 160'' above the limb. These waves can be traced to originate from a bright region of the on-disk part of the coronal hole where the propagation speed is in the range of (25 ? 1.3) km s-1 to (38 ? 4.5) km s-1, with the same periodicity. These on-disk bright regions can be visualized as the base of the coronal funnels. The adjacent plume region also shows the presence of propagating disturbance with the same range of periodicity but with propagation speeds in the range of (135 ? 18) km s-1 to (165 ? 43) km s-1 only. A comparison between the distance-time radiance map of both regions, indicate that the waves within the plumes are not observable (may be getting dissipated) far off-limb whereas this is not the case in the inter-plume region. A correlation analysis was also performed to find out the time delay between the oscillations at several heights in the off-limb region, finding results consistent with those from the analysis of the distance-time maps. To our knowledge, this result provides first spectroscopic evidence of acceleration of propagating disturbances in the polar region close to the Sun (within 1.2 solar radii), which provides clues to the understanding of the origin of these waves. We suggest that the waves are likely either Alfvénic or fast magnetoacoustic in the inter-plume and slow magnetoacoustic in plume regions. This may lead to the conclusion that inter-plumes are preferred channel for the acceleration of the fast solar wind.

Authors: G. R. Gupta, D. Banerjee, L. Teriaca, S. Imada, S. Solanki
Projects: None

Publication Status: Accepted for publication in APJ
Last Modified: 2010-05-20 15:17
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Accelerating waves in polar coronal holes as seen by EIS and SUMER

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