Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh44a..07b&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SH44A-07
Astronomy and Astrophysics
Astrophysics
[7507] Solar Physics, Astrophysics, And Astronomy / Chromosphere, [7509] Solar Physics, Astrophysics, And Astronomy / Corona, [7513] Solar Physics, Astrophysics, And Astronomy / Coronal Mass Ejections, [7531] Solar Physics, Astrophysics, And Astronomy / Prominence Eruptions
Scientific paper
We analyze the downflows in quiescent prominences with respect to width, vertical velocity and acceleration, using sequences of images from the Solar Optical Telescope (SOT) of the Hinode mission. SOT sequences in both 656.3 nm H-alpha and 396.8 nm Ca II H-line bandpasses show that the downflows have typical widths of 300 km, lengths up to 15 Mm, and speeds on the order of 10--20 km/s. Most downflows initiate near the top of the visible-light prominence in the form of bright knots and show an initial acceleration before achieving relatively constant speeds. Downflows typically end either in the chromosphere below the prominence or on large arches that sometimes form lower boundaries to the prominences. In some cases, downflows are strongly deflected by arches indicating a large gradient in the magnetic field at those locations. The vertical coherence of most of the threads over much of the prominence height suggests a continuous stream of plasma. The frozen-field condition implies the presence of vertical magnetic field dragged by the downflow with balanced up and down polarity. This explains the absence of vertical components in magnetic field measurements. The large-scale horizontal field plays an important role in the dynamics of the downflow, in two ways. It compresses the thread plasma and field and presents an obstacle to the downflow. The energy gained by falling in the gravitational field is in part expended in stretching the vertical field, in part in pushing the horizontal field out of the way and in part by covering the radiative losses of the compressed plasma. With total densities of the order of nearly 10^12 cm-3 and horizontal fields of order 10 G, energy and force balance yield vertical velocities of about 10 km/s and temperatures of 7000-8000 K. The threads are nourished by plasma inflow from outside the prominence along largely horizontal fields and sudden onset of gravitational instability.
Berger Thomas E.
Haerendel Gerhard
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