A Shock Surface Geometry: the February 15-16, 1967 Event

Tho flare associated interplanetary (IP) shock of February 15-16, 1967 observed by Explorer 33 and Pioneer 7 is analyzed to yield an estimntion of the ecliptic plane geometry of the shock surface near 1 AU. These spacocraft were separated by 23° in heliocentric longitude and Pioneer 7 was at a distance of 1.12 AU from the sun. There was an 18.9 hour delay between the two observations. The estimated shock normal, using a least squares shock parameter fitting procedure for the Explorer 33 data, is found to be 0PI = -53° and C, = 1980 which is close to the estimate of Hirshhbrg et al. (1970) of ined by using the magnetic coplanarity theorem and the Ames Research Center magnetometer data from Explorer 33. The (95% certainty) error cone angle for the shock normal of the Explorer 33 observation was approximately 7 ° . This severely inclined shock normal is not typical for IP shocks. The shock normal at Pioneer 7 position is found to be E -14° and OP = -161° using the magnetic coplanarity theorem and GSFC magnetic field data. However, the uncertainty is large (, 25 for I a cone angle). Although a data gap occurred at the apparent time of passage of the disturbance at Pioneer 6, which was 85 in heliocentric longitude from Pioneer 7 and at 0.83 AU, the recovered data did suggest such a passage. A consistent picture of the shock propagation is given to explain the difference in arrival times at Pioneers 6, 7, and Explorer 33 and the difference of the shock normals observed by Pioneer 7 and Explorer 33. The average shock speed from the sun to each spacecraft and the local speed at Explorer 33 and their relations to the position of the initiating solar flare are obtained and discussed. In the region of space between the Earth and Pioneer 7 the shock surface radius of curvature in the ecliptic plane was 0.4 AU or less.