Observational Evidence for Coronal and Interplanetary Shocks: The Workshop Events

Michael L. Kaiser

Abstract

There is a controversy surrounding solar shocks that cause type II radio bursts.  The controversy concerns the possible causal difference between the rather ubiquitous metric wavelength type II bursts in the low corona reported by ground-based radio observatories and the much longer wavelength interplanetary type II bursts reported by observers using spacecraft receivers.  Some researchers propose that the metric bursts are caused primarily by shocks associated with impulsive explosions, such as large flares, and are not driven by material.  These shocks die out relatively close to the sun.  Others would say that the metric bursts are caused by CMEs. On the other hand, hectometric to kilometric wavelength type II bursts at great distances from the sun (> 10 solar radii) are apparently all associated with CME-driven shocks.  The WAVES instrument on the Wind spacecraft covers a previously poorly explored decametric to hectometric wavelength range, between the usual spacecraft and ground-based bands.  WAVES can probe the solar altitude range down to perhaps 2 solar radii, well into the range where impulsive and CME-driven shocks might coexist, possibly producing two different type II bursts.  We examine the ground-based metric data and the WAVES decametric-hectometric data for the 28 workshop events to try to determine if the type II bursts observed in the two different wavelength regimes can be interpreted as one continuous event.  Our technique is to attempt to fit the observed drift rates and start times with existing (or slightly modified) coronal density models.

  Authors: M. L. Kaiser and M. J. Reiner

  Organization: NASA/Goddard Space Flight Center
     Telephone: 301-286-5461
           Fax: 301-286-1683
        e-mail: kaiser@panacea.gsfc.nasa.gov
       Address: Code 695
   Greenbelt, MD 20771