Climatological characteristics of the auroral ionosphere in terms of electric field and ionospheric conductance

The contributions of the north-south component of the electric field and the Hall conductance to the auroral electrojet are examined separately. For this purpose, 52 days of measurements from the Chatanika incoherent scatter radar, which was located near one of the standard AE stations, College, are utilized. A number of interesting characteristics of the auroralelectrojet system and auroral electrojet indices are noted: (1) The electric field distribution along the auroral region is roughly symmetric with respect to the 1100-2300 magnetic local time meridian. (2) The electric field, particularly the southward component, becomes a dominant feature along auroral latitudes with increasing magnetic activity. (3) The Hall conductance distribution in the postnoon sector is mainly determined by the Sun, thus making the eastward electrojet and the AU index dependent upon season. On the other hand, the Hall conductance associated with the major part of the westward electrojet in the midnight-postmidnight sector is controlled by precipitating electrons. (4) Since the Hall conductance of solar origin in the postnoon sector can be estimated, it would be possible to monitor electric field enhancements contributing to the eastward electrojet. By assuming the same electric field, except for the sign being applied to the westward electrojet, the AL index can be used to estimate the contribution of the Hall conductance associated with particle precipitation. This is a clear indication that the two indices, AU and AL, are governed by different physical processes. Thus it is recommended to use the two indices separately, rather than the combined AE, in monitoring the auroral electrojet system. (5) The Harang discontinuity seems to be a boundary separating the region of precipitating energetic particles on its northeast side from that of soft particles on its southwest side.