A view of the inner heliosphere during the may 10-11, 1999 - Low density anomaly

On May 10 and 11, 1999, near-Earth spacecraft observed the solar wind densi ty drop to below 0.1 particles cm(-3). Using those data, we have mapped sol ar wind parameters back to the Sun from 1 AU using two techniques. The firs t assumed constant-velocity trajectories plus corotation, while the second employed MI-ID-derived magnetofluid parameters. This inverse tracing create s a view of the inner heliosphere useful for identifying the source locatio n on the Sun of the density anomaly. We compare the two methods and show th at the source location of the anomaly predicted by MHD is mapped similar to 20 degrees eastward of the constant-velocity result. The coronal magnetic field maps indicate that the low density event occurred as the polar corona l magnetic field began reversing. We suggest that the event was initiated b y a latitudinal excursion of the low velocity heliospheric current sheet to ward the helioequator. The emergence of this dow flow into the preexisting faster wind produced strong rarefaction and anomalously low densities.