Physics – Plasma Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh51d..06s&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH51D-06
Physics
Plasma Physics
[2159] Interplanetary Physics / Plasma Waves And Turbulence, [7829] Space Plasma Physics / Kinetic Waves And Instabilities
Scientific paper
There is a growing body of evidence that the solar wind (and, by implication, generic weakly collisional plasmas) is marginal with respect to firehose and mirror instabilities. The question remains unanswered how this marginality is achieved. This question is not just interesting in itself, but also crucial for a plethora of astrophysical applications, where everything anyone cares about is some effective closure prescription suitable for modelling large-scale dynamics. The basic dilemma is whether pressure is isotropised via increased "anomalous" collisionality due to small-scale fluctuations at the stability boundaries or due to some rearrangement of the field structure effectively limiting the pressure anisotropy (equivalently the large-scale rate of strain). The choice is, roughly speaking, between less viscosity (=more collisions) or more viscosity (=limits on rate of strain). I will discuss (1) how one might construct the appropriate closures, (2) what we learn from the few cases in which analytical solution is available for the nonlinear evolution of the firehose and mirror fluctuations (no evidence of anomalous collisionality), (3) and how solar-wind observations might help us choose the right closures. Some relevant background references: 1. M. S. Rosin et al., MNRAS 413, 7 (2011) [e-print arXiv:1002.4017] 2. A. A. Schekochihin et al., MNRAS 405, 291 (2010) [e-print arXiv:0912.1359] 3. M. W. Kunz et al., MNRAS 410, 2446 (2011) [e-print arXiv:1003.2719] 4. A. A. Schekochihin et al., PRL 100, 081301 (2008) [e-print arXiv:0709.3828]
Cowley Stan
Kunz Martin
Rincon Felipe
Rosin M.
Schekochihin Alexander A.
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