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 13 ^ { th } 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 \arcsec 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 ~ { } \pm~ { } 14 ) km s ^ { -1 } just above the limb , to ( 330 ~ { } \pm~ { } 140 ) km s ^ { -1 } around 160 \arcsec 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 ~ { } \pm~ { } 1.3 ) km s ^ { -1 } to ( 38 ~ { } \pm~ { } 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 ~ { } \pm~ { } 18 ) km s ^ { -1 } to ( 165 ~ { } \pm~ { } 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 R/R _ { \odot } ) , 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 .