Theory and Simulations of Auroral Undulations Associated with Instabilities in the Dusk Sector Plasma Sheet

Ion drift wave theory and simulations of large-scale auroral undulations are presented for the observations in Lewis et al (2005). These undulations are identified as a nonlinear stage of the drift balloning-interchange mode in the presence of a sheared E×B flow for high Richardson's number in the dusk sector of the plasma sheet. The system is ideal MHD stable. Theoretical density, temperature and pressure profiles are constructed and constrained from data and used as input for a 2-1/2 D nonlinear Chebyshev-Fourier-tau pseudospectral code which reproduces the undulation structure to a good degree. Undulations were observed on February 6, 2002 along the equatorward edge of the auroral oval with the Far-Ultraviolet Wideband Imaging Camera on NASA's IMAGE satellite during the recovery phase of a moderate magnetic storm. The undulations occurred in the 18.5-14.5 magnetic local time sector between 63° and 71° magnetic latitude. Their wavelength and crest-to-base length averaged 292~km and 224~km, respectively; and they propagated westward with an average speed of 0.90±0.06~km/s. Such undulations are a relatively uncommon auroral phenomenon, and the mechanism that produce them and the magnetospheric conditions under which they occur are not well understood. Work supported by the National Science Foundation. [1] W.~S. Lewis, J.~L. Burch, J. Goldstein, W. Horton, J.~C. Perez, H.~U. Frey and P.~C. Anderson, submitted to GRL (2005).