Physics – Plasma Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh21c..06k&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SH21C-06
Physics
Plasma Physics
7800 Space Plasma Physics, 7811 Discontinuities, 7815 Electrostatic Structures, 7835 Magnetic Reconnection
Scientific paper
Magnetic holes are sudden depletions of solar wind magnetic field strength with durations of seconds to hours. First discovered with IMP 6 magnetic field observations in 1977, their origin, evolution and spatial structure are still subject to debate. Magnetic holes lasting on the order of hours have been studied extensively with field, plasma and composition experiments, most recently with ACE and Ulysses. Due to their large size relative to a proton gyroradius a fluid treatment is often employed to model these holes as pressure balanced structures. It is not clear that this can be extended to the smallest magnetic holes, where kinetic effects such as instabilities may play a dominant role. To date the short duration of kinetic-scale magnetic holes has placed them below the time resolution of existing ion instruments capable of measuring the velocity distributions needed to study kinetic phenomena. All observational details of kinetic-scale magnetic holes are based on magnetic field measurements and extrapolations of the features of large-scale holes. A method has been developed for extracting solar wind ion parameters once every 1.5 seconds from existing 90 second spectra recorded by the Wind/SWE Faraday Cup instruments since the start of the mission in 1994. In our first scientific application of this increased time resolution we report observations of ion properties within kinetic-scale magnetic holes. Characterizing the velocity distribution of protons as bi-Maxwellian distribution, we determine their density, velocity, and parallel and perpendicular temperatures. In these first-ever observations of the ion distribution function within kinetic-scale magnetic holes, observations are compared to a simple double adiabatic equation of state. Temperature anisotropy is discussed in terms of limits imposed by the firehose and mirror instabilities.
Kasper Justin Christophe
Lazarus Andrew J.
Seeluangsawat P.
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