Assessing the role of heavy ions in the dynamics of the near-Earth environment
Abstract
Changes in the ion composition throughout the Earth's magnetosphere can have profound implications on plasma structures and dynamics. The ratio of light to heavy ions has been shown to be highly dependent on geomagnetic activity, with the heavy ion content increasing with increasing activity, suggesting that ions of ionospheric origin can become the dominant species in the inner magnetosphere during disturbed times. Numerous studies focused on the transport and energization of O+through the ionosphere-magnetosphere system; however, relatively few have considered the contribution of N+ to the near-Earth plasma, even though past observations have established that N+is a significant ion species in the ionosphere and its presence in the magnetosphere is significant.
In spite of only 12% mass difference, N+ and O+ have different ionization potentials, scale heights and charge exchange cross sections. The latter, together with the geocoronal density distribution, plays a key role in the formation of ENAs, which in turn controls the energy budget of the inner magnetosphere and the overall loss of the ring current. Numerical simulations suggest that the contribution of N+to the ring current dynamics is significant, as the presence of N+, in addition to that of O+, alters the development and the decay rate of the ring current. Electron transfer collisions are far more efficient at removing N+the system, compared with O+ions. These findings suggest that differentiating the N+loss and transport from those of O+in the near-Earth environment has a profound impact on global magnetosphere dynamics,as plasma composition affects both the local and the global properties of the plasma. In addition, the presence of N+adds another frequency band for EMIC waves between the He+and O+cyclotron frequencies, which alters the dispersion characteristics of these waves. Observations show significant variation in density ratio and temperature anisotropy of heavy ions, and these variations can alter the threshold and the growth of the EMIC instability significantly. Based on frequency cutoff information, the concentration of nitrogen ions is found to be similar with those of oxygen ions during storm time.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSM23C..06I
- Keywords:
-
- 2720 Energetic particles: trapped;
- MAGNETOSPHERIC PHYSICSDE: 2772 Plasma waves and instabilities;
- MAGNETOSPHERIC PHYSICSDE: 2778 Ring current;
- MAGNETOSPHERIC PHYSICSDE: 2788 Magnetic storms and substorms;
- MAGNETOSPHERIC PHYSICS