Trans-auroral zone auroral infrasonic wave observations

The auroral infrasonic wave (AIW) substorm morphologies are compared for two trans-auroral zone stations, Inuvik, N.W.T. Canada (70°·4 dip lat) and College, Alaska (64°·6 dip lat), that lie along the same magnetic meridian with a north-south separation of 738 km. Statistical studies of the number of AIW received at College over a 5 yr period and at Inuvik over a 2 yr period as well as studies of individual auroral substorms observed at both stations have shown that in the morning sector many more AIW are observed at College than at Inuvik. This difference is related to the changing location of the westward auroral electroject with local time (Weins and Rostoker, 1973). The distribution of frequency of occurrence of AIW horizontal trace velocity V_η is presented for College data together with a discussion of the effects on the distribution of (1) source speed, (2) wind shear, (3) geometry of the AIW mach cone with respect to the observing station, (4) the filtering of AIW with high ray path apogees and (5) the decrease in AIW amplitude with increasing mach number.