Open AccessComment [on “The Parker Challenge”]
Author(s) -
Williams L. L.
Publication year - 2002
Publication title -
eos, transactions american geophysical union
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.316
H-Index - 86
eISSN - 2324-9250
pISSN - 0096-3941
DOI - 10.1029/2002eo000329
Subject(s) - magnetohydrodynamics , physics , plasma , coulomb , classical mechanics , mechanics , dissipation , electron , quantum mechanics
Fundamental to considering the relative merits of a ( B, V ) versus an ( E, j ) description of a plasma, one must first define the bulk fluid velocity and characterize the dissipation mechanism responsible for fluid cohesion. While the equations of magnetohydrodynamics (MHD) owe a heritage to studies of Coulomb‐collisionally dominated plasma, many geospace regions of interest are, in fact, Coulomb‐collisionless. Yet, the fluid equations of collisional MHD give a remarkably good and predictive description of this plasma. Still, collisionless plasma have qualities not captured by the collisional MHD paradigm, and their recognition requires an interpretation of the bulk fluid velocity that distinguishes the frozen‐in frame and the flux‐defined fluid velocity of conventional MHD.