New evidence for the origin of giant pulsations

We report on an extended interval of giant pulsation activity in the magnet osphere observed at multiple ground stations and in geosynchronous spacecra ft particle data. The pulsations display wave properties typical of previou sly reported giant pulsations, including reversal of phase across the latit ude of maximum amplitude as expected for field line resonances, comparable H (geomagnetic northward) and D (geomagnetic eastward) component amplitudes , and strong localization in latitude to within a few degrees. The recordin g of pulsation activity at numerous ground sites provides an opportunity to examine the local time dependence of the frequency of giant pulsations. We find that. throughout a long-lasting event, the frequencies of giant pulsa tions are fixed at particular local times but decrease systematically as lo cal time increases between midnight and noon. Geosynchronous proton fluxes between 100 and 150 keV oscillated at the same frequency as pulsations obse rved on the ground in the same local time sector. Nearly conjugate observat ions indicate the observed giant pulsations have odd spatial symmetry in th e magnetosphere. Calculations of the azimuthal wave number using three Nort hern Hemisphere stations and one Southern Hemisphere station also suggest t he observed giant pulsations have odd symmetry. Numerical calculations of r esonant particle energies and the combined ground and spacecraft observatio ns presented support the view that giant pulsations have odd spatial symmet ry and are driven by a population of particles in drift resonance.