Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...278..637l&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 278, no. 2, p. 637-643
Astronomy and Astrophysics
Astrophysics
4
Doppler Effect, Solar Atmosphere, Solar Wind, Space Plasmas, Sunspots, Angular Velocity, Charge Coupled Devices, Error Analysis, Solar Optical Telescope, Spectrographs
Scientific paper
Motions of slowly evolving sunspots and the rotation velocity of the plasma around them were determined within periods of one to three weeks each year from 1990 until 1992. The sunspots were divided into two classes depending on the size and number of proceeding and/or following umbrae. Most of the sunspots were Zuerich type H, too large and complex sunspots were rejected. The main aim was a determination of plasma and sunspot velocities within larger fields of activity and a search for special patterns of plasma flows, which may be caused by interaction of the magnetized and unmagnetized plasmas. Around a total of 34 sunspots about 130 plasma velocity fields with sizes of about 120 by 70 arcseconds could be scanned. Within these fields the plasma rotation velocity was determined using the non-split solar spectral line at 5576 A with respect to laboratory iodine lines for an array of 400 by 240 points. The averaging of sub-fields +5 degrees in longitude (west) of the sunspots compared with those -5 degrees (east) of the sunspots showed a difference of 50 m/s to 70 m/s for the mean values with the same sign and about the same values for the two classes of sunspots selected. The amount of this determined asymmetry of the plasma rotation velocities in longitude depends on the excess rotation velocity of the sunspots as compared to the mean plasma rotation velocity at the latitudes where the sunspots were observed. While no dependence on the longitude distribution of the sunspots could be found, there is for both classes fo sunspots a more pronounced asymmetry of the plasma rotation velocity in the southern as compared to the northern hemisphere. Systematic errors are discussed and excluded. Some attempts are given to explain the new findings.
Lustig G.
Woehl Hubertus
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