Open AccessReduced dynamical equations for the high‐latitude thermosphere: Ion drag balance
Author(s) -
Kinney R. M.,
McWilliams J. C.
Publication year - 1999
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1999ja900007
Subject(s) - thermosphere , physics , drag , mesoscale meteorology , nonlinear system , mechanics , classical mechanics , computational physics , geophysics , ionosphere , meteorology , quantum mechanics
Although highly variable on small scales, the middle thermosphere shows evidence of slow‐timescale mesoscale dynamics. A reduced set of equations is derived by asymptotic scale analysis. The drag‐balance equations describe the nonlinear evolution of the thermosphere during magnetic quiet times under an approximate balance of pressure, Coriolis, and ion‐drag forces. The equations explicitly remove gravity and sound oscillations, making them well suited for theoretical study of slow‐timescale evolution and efficient for numerical modeling. Linear analysis is used to establish the limits of their validity in terms of timescale separation. The slow‐timescale component is only weakly damped for horizontally broad motions, even when the ion‐neutral collision frequency is large.