The relationship between EMIC waves, long period ULF waves and wave generation processes in the middle magnetosphere
Abstract
Electromagnetic Ion Cyclotron (EMIC) Waves are important in magnetospheric wave-particle interactions leading to depletion of radiation belt MeV electron populations and erosion of ring current keV ions. Pearl-EMIC waves often exhibit regular time varying amplitude, sometimes appearing as discrete packets of wave energy. The mechanism responsible for this amplitude structure is unclear but may relate to changes in the wave generation growth rate. These EMIC waves are often observed in conjunction with Pc5 ULF waves, particularly around times of increased geomagnetic activity and geomagnetic storms. Previous results from the CRRES satellite magnetometer data have provided examples where Pearl-EMIC waves coexist with long period compressional Pc5 waves where the amplitude of the EMIC wave appears to be related to the Pc5 wave phase. Pearl-EMIC waves are also seen with thermal and energetic protons and heavier oxygen and helium ions, both with and without the presence of longer period Pc5 oscillations. Linear and non-linear wave growth theory indicate that these heavy ion populations can both damp or increase EMIC wave growth, depending on the ion composition. These factors, when considered individually, have not consistently explained the pearl-EMIC packeting structure. However together they may provide a sufficient explanation.
Example EMIC events will be presented from the Van Allen probe data to illustrate that there is an in-phase or anti-phase relationship between the timing of the EMIC packets and the phase of Pc4/5 along with cold and energetic heavy ions and observed density modulation similar to the EMIC packet repetition rate and Pc4/5 frequency. Hybrid simulations are used here to examine both the individual and combined effects of heavy ions and long period hydromagnetic waves on EMIC wave growth. Results indicate that either process can increase the amplitude of the EMIC modulation but together may strengthen or inhibit it completely. These results will be discussed and compared with the events seen in the Van Allen Probes data.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSM51H3262W
- Keywords:
-
- 2730 Magnetosphere: inner;
- MAGNETOSPHERIC PHYSICS;
- 2752 MHD waves and instabilities;
- MAGNETOSPHERIC PHYSICS;
- 2772 Plasma waves and instabilities;
- MAGNETOSPHERIC PHYSICS;
- 2774 Radiation belts;
- MAGNETOSPHERIC PHYSICS