| Summary: | Large auroral and ionospheric databases, covering a solar cycle (1978-1986), were used to obtain a comprehensive evaluation of the auroral electrojet effect (as inferred from the auroral AE-index) on the ionospheric response in both hemispheres from sub-auroral to equatorial latitudes. The study was limited to the East Asian-Australian longitudinal sector where data are available from a chain of nine latitudinally displaced stations. Enhancement in the standard ionospheric parameter, the virtual height of the F-region (Delta h'F) recorded by vertical-incidence ionosondes. was used to trace the ionospheric disturbance. Unlike the previous studies of this type, the total magnetic and ionospheric data, in hourly intervals, were used to derive the correlation coefficient r between two intrinsically different parameters: Delta h'F and AE-index for the local nighttime (20-06 LT or 10-20 UT). A suitable averaging and smoothing technique was applied to the data to enhance the correlation trend between these parameters. It is evident that the height fluctuations of sub-auroral ionosphere (for stations: Yakutsk in Siberia and Hobart and Canberra in Australia) closely resemble the auroral electrojet surges, inferred from the AE-index over the solar cycle. The linear coefficient r is highly significant, being close to 0.6 for most of the time; during the years of maximum auroral activity (1981-1983) r approached 0.8. The consistently high correlation r, regardless of the season, applies only to the most poleward station used in this study, Yakutsk. The sub-auroral stations (Hobart and Canberra) positioned further equatorwards show a strong decline in the correlation coefficient r during the local summer but have high r during winter and the equinoxes. There is a general decline in r towards lower latitudes, suggesting that the response to auroral substorms is on the whole diminishing with the distance from the auroral source to the equator. There appears to be an anomalous increase in r as observed around 10 degrees invariant latitude. These findings appear to be the first long-term proof of the symmetry of the ionospheric responses to auroral substorm activity in the northern and southern auroral ovals which is an important contribution to space climatology. It is suggested that the aurorally generated acoustic gravity waves (AGWs), manifested in the global ionosphere as large scale travelling ionospheric disturbances (LSTIDs), may contribute to the observed auroral-ionospheric phenomena. (C) 1999 Elsevier Science Ltd. All rights reserved.
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