THE TEMPERATURE-DEPENDENT NATURE OF CORONAL DIMMINGS

Journal Article · Wed Sep 01 00:00:00 EDT 2010 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/720/1/L88· OSTI ID:21452841

Robbrecht, Eva ^[1]

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1. Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels (Belgium)

The opening-up of the magnetic field during solar eruptive events is often accompanied by a dimming of the local coronal emission. From observations of filament eruptions recorded with the Extreme-Ultraviolet Imager on STEREO during 2008-2009, it is evident that these dimmings are much more pronounced in 19.5 nm than in the lower-temperature line 17.1 nm, as viewed either on the disk or above the limb. We conclude that most of the cooler coronal plasma is not ejected but remains gravitationally bound when the loops open up. This result is consistent with Doppler measurements by Imada and coworkers, who found that the upflow speeds in a transient coronal hole increased dramatically above a temperature of 1 MK; it is also consistent with the quasistatic behavior of polar plumes, as compared with the hotter interplume regions that are the main source of the fast solar wind. When the open flux reconnects and closes down again, the trapped plasma is initially heated to such high temperatures that it is no longer visible at Fe IX 17.1 nm. Correspondingly, 17.1 nm images show a dark ribbon or 'heat wave' propagating away from the polarity inversion line and coinciding with the brightened Fe XV 28.4 nm and Fe XII 19.5 nm post-eruptive loops and their footpoint areas. Such dark ribbons provide a clear example of dimmings that are not caused by a density depletion. The propagation of the 'heat wave' is driven by the closing-down, not the opening-up, of the flux and can be observed both off-limb and on-disk.

• OSTI ID: 21452841
• Journal Information: Astrophysical Journal Letters, Vol. 720, Issue 1; Other Information: DOI: 10.1088/2041-8205/720/1/L88; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
EMISSION
ERUPTION
EXTREME ULTRAVIOLET RADIATION
MAGNETIC FIELDS
PLASMA
SOLAR CORONA
SOLAR FLARES
SOLAR RADIATION
SOLAR WIND
SUN
TEMPERATURE DEPENDENCE
ATMOSPHERES
ELECTROMAGNETIC RADIATION
MAIN SEQUENCE STARS
RADIATIONS
SOLAR ACTIVITY
SOLAR ATMOSPHERE
STARS
STELLAR ACTIVITY
STELLAR ATMOSPHERES
STELLAR CORONAE
STELLAR FLARES
STELLAR RADIATION
STELLAR WINDS
ULTRAVIOLET RADIATION