Polar Plumes Observed at Extreme Coronal Altitudes

Details Polar Plumes Observed at Extreme Coronal Altitudes Polar Plumes Observed at Extreme Coronal Altitudes

Sep 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...19410801d&link_type=abstract

American Astronomical Society Meeting 194, #108.01

Astronomy and Astrophysics

Astronomy

1

Scientific paper

Polar plumes, unipolar high density structures in the polar coronal holes, are key to our understanding of solar wind acceleration and coronal heating. Because unipolar magnetic flux concentrations in the coronal hole account for approximately 50 leaves the coronal hole (DeForest et al., 1996), plumes (which arise from some such concentrations) are tracers of a type of magnetic structure that fills nearly half of the solar system at solar minimum. Plumes have been observed up to altitudes of about 10 solar radii with the LASCO instrument (DeForest et al., 1996), above which they fade into the coronal background. There is some contention (Habbal and Woo, 1997; Paetzold and Bird, 1998) over whether plumes extend into the interplanetary medium or become mixed with the interplume solar wind at altitudes between 10 and 100 solar radii. Several mechanisms, including the Kelvin-Helmholtz two-stream instability and cross-mode resonant wave scattering near the alfvenic point in the wind's acceleration, have been proposed that could break up the structure of the observed plumes. Using the LASCO C-3 instrument aboard SOHO (Brueckner et al, 1995) to accumulate multiple images that we then recombine, we have generated coronal images with effective exposure times in the thousands of seconds and actual durations of less than four hours. These images clearly show polar plumes extending to altitudes of 25 solar radii or more, very close to the outer edge of the C-3 field of view and above the likely alfvenic point of the wind flow.

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