Observation of the Solar Wind and Magnetosphere Interaction Near the Subsolar Point During Active Geomagnetic Periods on October 24 and 31, 2003

In October of 2003 the major axis of the IMAGE spacecraft's orbit was roughly aligned with the Sun-Earth line, with a dayside apogee extending approximately eight Earth radii from the Earth. This fortuitous orientation provided the opportunity to make measurements near the nose of the magnetosphere. Starting at ∼1530 UT on October 24 and again at ∼0530 UT on October 31---both periods of elevated geomagnetic activity---the LENA telescope on IMAGE recorded high counting rates of nominal ∼keV neutral hydrogen distributed in an unusually wide angular distribution centered on the Sun. These LENA signals are unique to these two periods and concurrent plasma and neutral atom measurements from the RPI and HENA instruments on IMAGE also reveal unusual, difficult to explain features. We use solar wind particle measurements from the SWEPAM instrument on the ACE spacecraft to compare the solar wind flux and thermal spread with the LENA data and as an input into magnetopause and bow shock models. These models show magnetospheric contractions that are well aligned with variations in the IMAGE observations, suggesting that the spacecraft may have entered the supersonic solar wind. Although this interpretation explains many of the observations, we continue to examine alternative explanations suggested by some features in the data. We also study the possibility of a connection between the unusual LENA observations and a similar, commonly observed diffuse signal thought to arise from solar wind charge exchange in the magnetosheath