The background cold electron density plays an important role in plasma and wave dynamics. Here, we investigate an event with clear modulation of the particle fluxes and wave intensities by background electron density irregularities based on Van Allen Probes observations. The energies at the peak fluxes of protons and Helium ions of 100 eV to several keV are well correlated with the total electron density variation. Intense electromagnetic ion cyclotron (EMIC) and magnetosonic (MS) waves are simultaneously observed in the high-density regions and disappear in low-density regions. Based on the linear theory of wave growth, the EMIC waves are generated by the ~10 keV protons, while most MS waves are generated by the positive gradient of proton phase space density at several hundred eV in the high-density regions. Our results indicate the importance of background plasma density structures in generation of plasma waves by unstable ion distributions.
Bibliographical noteFunding Information:
This work was supported by National Natural Science Foundation of China (41974191), China Space Agency Project D020303 and Ministry of Science and Technology project 2020YFE0202100. The work at UCLA was supported by RBSP-ECT and EMFISIS funding provided by JHU/APL Contracts 967399 and 921647 under NASA's Prime Contract NAS5-01072 and by NASA Grants NNX16AG21G, NNX15AI96G, NNX14AN85G, and NNX14AI18G. Q. M. would like to acknowledge the NASA Grant 80NSSC20K0196. We thank the EMFISIS team for providing wave data from the Van Allen Probe spacecraft which was supported by JHU/APL Contract 921647 under NASA Prime Contract NAS5-01072 and JHU/APL Contract 131802 under NASA prime Contract NNN06AA01C. We acknowledge use of Van Allen Probes data of the Level 3 HOPE pitch angle dependent particle flux data obtained from the RBSP-ECT website (https://rbsp-ect.newmexicoconsortium.org/data_pub/rbspa/hope/level3/pitchangle/) and EMFISIS data obtained from http://emfisis.physics.uiowa.edu/Flight/. We thank the Space Physics Data Facility at the NASA Goddard Space Flight Center for providing the OMNI data (https://cdaweb.gsfc.nasa.gov/index.html/).
- electromagnetic ion cyclotron
- electron density irregularities
- magnetosonic waves
- suprathermal particles
- wave growth rate
- wave-particle interaction