Auroral kilometric radiation and the auroral electrojet index for the January 1997 magnetic cloud event

Auroral kilometric radiation (AKR) observations by Polar and Geotail are compared with the auroral electrojet index for the January 1997 magnetic cloud event. These two‐spacecraft measurements are complementary in covering the AKR emission cones throughout the event and, together, reasonably represent the auroral electrojet A E index. We point out, however, limitations of both the AKR index and the A E index in providing truly global measurements of substorm activity.