Ring-Current Ion Angular Distributions: CAMMICE Observations

The evolution of ring current ion angular distributions is important to understanding transport and loss process. It is also important for understanding ENA images. Chen et al. Compared 40 - 150 keV proton pitch angle distributions with simulations involving transport and charge exchange losses (Chen et al., 1998, 1999). The He+ and O+ ions were not examined in those papers. Recent work has shown that at lower energies (below 5 to 25 keV) the ring current ions often have field aligned angular distributions in the inner magnetosphere. In the current study we examine the ring current ion angular distributions for H+, He+, He++ and O+ over the wide energy range (1 to 200 keV/q) covered by the Polar CAMMICE observations. For example, during a quiet period on 9 May 1999 the H+ and He+ angular distributions at 40 keV/q could be represented by Sin^N(alpha) with N=0.6 and 2.9 respectively at L=3.5 while N=0.25 for both near L=6.5. During quiet times, the O+ fluxes were too low to obtain a valid fit on short time scales. During the May 4, 1998 magnetic storm CAMMICE observed bi-directional field-aligned < 10 keV H+, He+ and O+ ions for more than 30 minutes at L<6 Re while observing distributions peaked at 90 deg. for higher energies. We will provide such snapshots of the ring current ion angular distributions during both quiet and storm times plus statistical average angular distributions for the dominate species.