STRONG HYDROMAGNETIC TURBULENCE ASSOCIATED WITH COMET GIACOBINI-ZINNER

The turbulence surrounding comet Giacobini-Zinner reached intensities three orders of magnitudes above that of 'intermediate' solar wind conditions, was characterized by DELTA B/B//o almost equal to one, and extended to cometocentric distances beyond 10**6 km. The strong spectral peak at f approximately 10** minus **2 Hz and the general intensity profile of the turbulence (a lack of emissions close to the nucleus less than 2. 5 multiplied by 10**4 km! , peak intensities near the bow wave, and a spatial extend greater than 10**6 km) are in excellent agreement with generation by plasma instabilities associated with the pickup of H//2O** plus group ions. The total energy of the magnetic turbulence near f to approximately 10** minus **2 Hz is estimated to be approximately 5 multiplied by 10**1**5 joules and that of ion energization due to solar wind pickup approximately 6 multiplied by 10**1**3 watts. It thus takes a minimum of approximately 100 s to build up the magnetic turbulence. This scale is approximately the linear growth rate of the ion pickup instability, giving a consistent picture of the energy source of the turbulence.