Cusp latitude magnetic impulse events: 3. Associated low‐latitude signatures

Abstract

Low‐latitude magnetic perturbations at San Juan, Puerto Rico, occurring simultaneously with the set of South Pole magnetic impulse events (MIEs) discussed by Lanzerotti et al. (1991) and Konik et al. (1994) are examined. The amplitudes of the magnetic deflections at the times of the MIEs at South Pole and at San Juan are compared to the magnetic deflections seen at these two stations during storm sudden commencements (SSCs). At the South Pole, we find the mean deflections in the magnetic H and V components to be larger for the MIEs than for the SSCs. At San Juan, we find the opposite to be true; the mean amplitudes of the deflections in the H and V components of the field are much smaller during the MIEs than during the SSCs. The interplanetary plasma conditions prevailing at the times of the MIEs are also examined and contrasted to those found during SSCs. We find that while the MIEs are characterized by changes in the solar wind dynamic pressure at the noise level, the SSCs are concurrent with large changes in the dynamic pressure. Examining the correlations between MIE amplitudes and dynamic pressure changes, we find no correlation for the MIE deflections at the South Pole, but a strong correlation for the concurrent deflections seen at San Juan. In contrast, we find strong correlations between SSC amplitudes and dynamic pressure changes at both the South Pole and San Juan. We conclude that the MIE signatures at the South Pole are not predominantly generated by dynamic pressure fluctuations, and that the concurrent ground magnetic signatures at San Juan are unrelated to those at the South Pole. We also examine our data in order to deduce any amplitude dependence upon local time and in particular whether larger ground signatures are found in local morning than in local afternoon. We find that for both the sets of MIEs and SSCs, the amplitudes of deflections at the South Pole exhibit no significant local time pattern.