Quantitative determinations are made of the correlation coefficients and their standard deviations between variations in the cosmic noise absorption by the ionosphere and variations in magnetic field in the period range ~20-100 s, as measured at Siple, Antarctica. Several intervals during four magnetic storms were identified where the correlations were significant at the 3-4&sgr; level. During a number of these intervals the correlations between the magnetic field fluctuations in the northern and the southern hemisphere are <2? and often <1&sgr;. The magnitudes of the magnetic field fluctuations together with the absorption variations are consistent with changes in the ionospheric conductivity at ~100 km produced by particle precipitation. The particle precipitation may at times be evidence of the modulation of particle pitch angle distributions by highly localized hydromagnetic waves in the earth's magnetosphere.