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Soho Observations of Density Fluctuations in Coronal Holes |
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| Authors: | L Ofman M Romoli G Noci G Poletto J L Kohl R A Howard C St Cyr C E Deforest |
| Institution: | (1) Raytheon ITSS and NASA GSFC, Code 682, Greenbelt, MD 20771, USA;(2) Dept. of Astronomy, University of Florence, Largo Fermi 5, I-50125 Florence, Italy;(3) Arcetri Observatory, Largo Fermi 5, I-50125 Florence, Italy;(4) Harvard Smithsonian CfA, 60 Garden St, Cambridge, MA 02138, USA;(5) Naval Research Lab., Code 7660, Washington, DC, 20375, USA;(6) Naval Research Lab and NASA GSFC, Code 682, Greenbelt, MD 20771, USA;(7) Stanford University and NASA GSFC, Code 682, Greenbelt, MD 20771, USA |
| Abstract: | In recent UVCS/SOHO White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes at heliocentric distances of 1.9 to 2.45 solar radii. The motivation for the observation is the 2.5D MHD model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes. In February 1998 we performed new observations using the UVCS/WLC in the coronal hole and obtained additional data. The new data corroborate our earlier findings with higher statistical significance. The new longer observations show that the power spectrum peaks in the 10–12 minute range. These timescales agree with EIT observations of brightness fluctuations in polar plumes. We performed preliminary LASCO/C2 observations in an effort to further establish the coronal origin of the fluctuations. This revised version was published online in June 2006 with corrections to the Cover Date. |
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