Low‐latitude particle precipitation and associated local magnetic disturbances

The time variations of optical emissions during low‐latitude auroral events have been shown to correlate well with those of magnetograms in the region where the aurorae are observed. Two events not previously reported are analyzed and are shown to confirm the nature of the correlations found for two earlier events. The maximum optical emissions at mid‐latitudes occur in concert with the maximum positive (northward) excursions in the H trace and with rapid fluctuations in the D trace of nearby magnetograms. The fluctuation in Δ D is usually from the east (positive) to the west (negative) in vicinity of the Δ H perturbation. The positive excursions in H at low‐latitude observatories at the time of the maximum optical emissions are associated with negative H excursions at higher‐latitude observatories in the same longitude sector. The source of the particles has been inferred to be the ring current, with precipitation occurring when the | Dst | index is large at the time of the large short term excursions in the local magnetic field. This result is consistent with the finding of Voss and Smith (1979), derived from a series of rocket measurements of precipitating heavy particles, that the flux correlates better with the product of | Dst | and the exponential of K p than with either alone. In the present case it is shown that the product of | Dst | and the amplitude of the short term excursions in the horizontal component in local magnetograms has better time resolution and better correlation with the observed emission rates than the index using K p .