Auroral orientation curves and the auroral oval I

A comparison has been made between the auroral orientation curves and the auroral oval determined from the occurrence of the aurora. It has been found that the auroral orientation curve crossing the midnight meridian at 67° corrected geomagnetic latitude is located within the auroral oval. The largest difference between the location of the auroral oval and the 67° curve occurs in the morning hours and it has been argued that the auroral orientation curve gives a better definition of the true auroral oval in this time interval. The auroral orientation curves have also been related to the hydrogen emission and it has been found that the 66° curve of auroral orientation represents the oval of hydrogen emission except in the morning hours, where the data are ambiguous.