HR: 0830h
AN: SH21B-0139    [PDF]
TI: A Simulation Study of the May 10-11, 1999 Low Density Anomaly
AU: * Usmanov, A V
EM: arcadi.usmanov@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Code 692, Greenbelt, MD 20771 United States
AU: Goldstein, M L
EM: arcadi.usmanov@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Code 692, Greenbelt, MD 20771 United States
AU: Ogilvie, K W
EM: keith.w.ogilvie@nasa.gov
AF: NASA Goddard Space Flight Center, Code 692, Greenbelt, MD 20771 United States
AU: Farrell, W M
EM: melvyn.l.goldstein@nasa.gov
AF: NASA Goddard Space Flight Center, Code 695, Greenbelt, MD 20771 United States
AU: Lawrence, G R
EM: grl@kreutz.nascom.nasa.gov
AF: NASA Goddard Space Flight Center, Code 682.3, Greenbelt, MD 20771 United States
AB: On May 10-11, 1999 solar wind density dropped to anomalously low values of $\sim$0.1~cm$^{-3}$. The density depletion occurred on a relatively slow wind background in between of faster flows and was apparently not associated with a coronal mass ejection or a fast corotating stream. While magnetic field intensity did not show a notable variation across the depletion, the SWEPAM analyzer on the ACE spacecraft revealed an abnormally strong non-radial flow component, with the azimuthal speed peaking at $\sim$100~km~s$^{-1}$. {\it Usmanov et al.} [2000] suggested that the density anomaly was in fact a rarefaction on the trailing edge of a relatively faster flow and that the rarefaction formed as a result of suppression of coronal outflow from a region that earlier provided the faster solar wind. The suppression in turn was supposed to appear due to a quick restructuring of solar magnetic fields during polar field reversal. In present work, we show results of a two-dimensional time-dependent MHD simulation in the equatorial plane with initially longitude-homogeneous Parker solar wind and spiraling magnetic being disturbed by a slower velocity/higher density pulse on an inner computational boundary at 20 solar radii. We follow the development and propagation of the rarefaction out to Earth orbit and compare pseudo-time series with ACE measurements. We show that a strong rarefaction indeed can develop behind faster flow and that simulation results and ACE observations are in good agreement. The simulated radial magnetic field shows a relatively small variation across the density anomaly compared to that in density. The stream interaction generates strong azimuthal velocities in the slow flow region, as observed. The simulation shows also a sub-Alfv\'enic flow region embedded into the low density region. The sub-Alfvenic region does not extend all the way to the Sun, but gets disconnected as the depletion propagates to Earth orbit.
DE: 2134 Interplanetary magnetic fields
DE: 2164 Solar wind plasma
DE: 2169 Sources of the solar wind
DE: 7509 Corona
DE: 7511 Coronal holes
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting