Response of neutral atom emissions in the low-latitude and high-latitude magnetosheath direction to the magnetopause motion under extreme solar wind conditions

[1] On 11 April 2001 the high velocity and density of the solar wind and the strong southward interplanetary magnetic field moved the dayside magnetopause inside of geosynchronous orbit. The Low Energy Neutral Atom (LENA) imager on the Imager for Magnetopause-to-Aurora Global Exploration ( IMAGE) spacecraft in the magnetosphere observed significant emission in the magnetosheath direction. The total neutral atom flux from the dayside region, ignoring the neutral solar wind flux directly from the Sun, shows a threefold enhancement, and each of the three increases is coincident with the occurrence of the magnetopause inside 6.6 R-E. Observations by LENA also show that emission in the direction of the low-latitude and high-latitude magnetosheath is modulated in such a manner that the sources shift earthward/sunward and equatorward/ poleward in the low-latitude and high-latitude sheath, respectively. A model based on the distributions of the sheath flux and of the number density of the hydrogen exosphere explains these characteristics as a result of the motion of the magnetopause having an indentation at the cusp, suggesting a means for monitoring the cusp motion using IMAGE/LENA.