SH53B-2511
Ion-Driven Instabilities in the Solar Wind: Wind Observations of 19 March 2005
Friday, 18 December 2015
Poster Hall (Moscone South)
S Peter Gary, Los Alamos National Laboratory, Los Alamos, NM, United States, Lan Jian, University of Maryland College Park, College Park, MD, United States, Thomas W Broiles, Southwest Research Institute, San Antonio, TX, United States, Michael Louis Stevens, Smithsonian Astrophysical Observatory, Cambridge, MA, United States, John J Podesta, Space Science Institute Boulder, Center for Space Plasma Physics, Boulder, CO, United States and Justin Christophe Kasper, University of Michigan, Ann Arbor, MI, United States
Abstract:
Analysis of magnetic field measurements from the Wind spacecraft under the relatively slow (flow speed ~ 390 km/s) solar wind conditions of 19 March 2005 demonstrates seven events of enhanced magnetic fluctuations at spacecraft-frame frequencies somewhat above the proton cyclotron frequency and propagation approximately parallel or antiparallel to the background magnetic field Bo. Plasma measurements from Wind show that the proton velocity distributions during these events are characterized by two components: a more dense, slower core and a less dense, faster beam. Average plasma parameters are used in the kinetic linear dispersion equation for fluctuations at k x Bo = 0; the results show one event is weakly unstable to the left-hand polarized Alfven-cyclotron instability driven by the proton core temperature anisotropy Tperp/T|| > 1, and four events are weakly unstable to the right-hand polarized magnetosonic instability driven by the beam/core relative flow. Although solar wind instabilities driven by proton temperature anisotropies have been studied extensively, these results suggest that the beam/core magnetosonic instability is a likely source of many of the observed proton-cyclotron events and is worthy of further attention.
