Impulsive events marked by durations ranging from 5 to 15 min and peak-to-peak variations in the H component exceeding 40 nT are common in observations by high-latitude dayside ground magnetometers. We survey observations by a global network of high-latitude ground magnetometers to distinguish between their proposed causes. Peak event amplitudes and occurrence rates occur prior to local noon in the range of geomagnetic latitudes from 70¿ to 76¿. Although most events can be associated with abrupt changes in the interplanetary magnetic field (IMF) orientation, few can be associated with abrupt changes in the solar wind dynamic pressure. Many events can be observed during intervals of steadily northward IMF orientation, but only a few can be observed during intervals of steadily southward IMF orientation. We suggest an interpretation of the events in terms of a model in which changes in the IMF orientation modulate the fraction of the solar wind pressure applied to the magnetosphere. ¿ American Geophysical Union 1996