Could We Have Forecast "The Day the Solar Wind Died"?

Abstract

In 1999 May an interval of unusually slow (<300 km s^-1) and rarefied (<1 cm^-3) solar wind was observed upstream of Earth by the ACE spacecraft. The event has been dubbed "The Day the Solar Wind Died." We apply our solar wind forecast model to the interval in question, to ask whether we could have predicted the phenomenon. The model fails, but by the manner in which it fails, we support the conclusion that the rarefaction was caused by a suppression of coronal outflow from a region that earlier provided fast wind flow, possibly caused by a rapid restructuring of solar magnetic fields.