| Summary: | One hundred and sixty-one sudden increases in auroral riometer absorption (SAI events), recorded over three years, were compared for two conjugate stations : Macquarie Island (L-value = 5.2) and College (L-value = 5.2), located in the southern and northern auroral zones, respectively. Additional riometer data, from two more auroral stations (Syowa Base, (L-value = 6.1) and Kiruna, L-value = 5.4), were used to deduce the drift velocities of the absorption events. It is evident that the SAI events tend to occur closely in time at the conjugate stations before the local magnetic midnight. They propagate mainly westward with average velocities 2.7 4.5 km s 1. The longitudinal position of the conjugate point to Macquarie Island was verified using absorption drift considerations. There arc appreciable hemispheric differences in the auroral absorption levels at College and Macquarie Island, consistent with the previous results on the relative auroral absorption and luminosity magnitudes at the conjugate locations. The cases of a complete conjugacy breakdown, detected during the southern winter solstice period, appear to be related to a seasonal change in the latitude (L-value) of the conjugate point location.
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