Distribution of Auroras in the Southern Hemisphere. II. Nightly Probability of Overhead Aurora

The probability P of overhead occurrence of aurora during a night is estimated for 22 southern hemisphere stations during the I.G.Y. The distribution of probability of occurrence is represented in terms of three measures of colatitude: 81 is defined in terms of the eccentric dipole representation of the geomagnetic field; 82 is defined in terms of projections from circles in the equatorial plane, along the geomagnetic lines of force, onto the Earth; 83 is defined in terms of the integral invariant f; (I-F IF m)!dl of charged particle motion in the geomagnetic field.