Polar Magnetic Substorms 03 - 06 Ut December 5,1968

Magnetic effects associated with a westward travelling surge are illustrated by analysis of simple bays which occurred during three moderately weak substorms, 03 - 06 U.T. on December 5, 1968. South of the electrojet centre, at <t>= 57°, magne tic effects are shown to be attributable solely to the auroral electrojet and i ts return curren ts. The azimuth of the Thule current vector, previously shown to reflecc the westward extension of the electrojet in the auroral oval, is used to identify individual substorms, to estimate the rate of westward rotation of the oval, and to distinguish between trigger and main bays. Ail storms show a rapid decay and eastward swing in the final phase. The westward rotation of the oval, deduced from the azimuth of the Thule vector and the velocity of the D demarcation line, is found to be highly irregular.