The interplanetary shock of September 24, 1998: Arrival at Earth

At close to 2345 UT on September 24, 1998, the magnetosphere was suddenly c ompressed by the passage of an interplanetary shock. In order to properly i nterpret the magnetospheric events triggered by the arrival of this shock, we calculate the orientation of the shock, its velocity, and its estimated time of arrival at the nose of the magnetosphere. Our best fit shock normal has an orientation of (-0.981 -0.157 -0.112) in solar ecliptic coordinates , a speed of 769 km/s, and an arrival time of 2344:19 at the magnetopause a t 10 R-E. Since measurements of the solar wind and interplanetary magnetic field are available from multiple spacecraft, we can compare several differ ent techniques of shock-normal determination. Of the single spacecraft tech niques the magnetic coplanarity solution is most accurate and the mixed mod e solution is of lesser accuracy. Uncertainty in the timing and location of the IMP 8 spacecraft limits the accuracy of solutions using the time of ar rival at the position of IMP 8.