Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sh41b12n&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SH41B-12
Physics
2134 Interplanetary Magnetic Fields, 2139 Interplanetary Shocks, 7509 Corona, 7851 Shock Waves
Scientific paper
In order to investigate the seemingly poor correlation between coronal and inter-planetary (IP) shocks we examined the characteristics of the ambient medium through which the shocks propagate. We looked at a series of metric type II bursts from June 1997 through July 2000 and created a profile of the fast mode speed from the inner corona to IP space. We generated a map of the Alfven speed, the dominant coronal speed, by calculating radial magnetic and density variations using magnetic data from the Michelson Doppler Imager (MDI) with density information supplied by the Extreme Ultraviolet Imaging Telescope (EIT), both aboard the Solar and Heliospheric Observatory (SOHO). In quiet regions of the low corona a typical Alfven speed for a magnetic field of 1 G and a density of ~5 *E8 cm-3 is ~175Km/S, this number rises to ~4000Km/S in active regions, where the magnetic field can be 100 G with densities ~3 x 109 cm-3. We find that the Alfven speed peaks in the middle corona and falls off in the outer corona, beyond which the solar wind speed becomes the dominant speed. To generate a profile of the wind speed from the outer corona to 30 solar radii we used data from the Large Angle Spectrometric Coronagraph (LASCO) aboard SOHO. The mid-coronal hump in the Alfven speed seems to contribute to the poor correlation between coronal and IP shocks as the majority of coronal shocks become MHD waves as they propagate through that area. As the dominant speed drops beyond the middle corona, shock waves form more easily, and normal waves can once again form shock waves in IP space.
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