TY - JOUR
T1 - Test of Ion Cyclotron Resonance Instability Using Proton Distributions Obtained From Van Allen Probe-A Observations
AU - Noh, Sung Jun
AU - Lee, Dae Young
AU - Choi, Cheong Rim
AU - Kim, Hyomin
AU - Skoug, Ruth
N1 - Funding Information:
This research at Chungbuk National University was supported by the National Meteorological Satellite Center of Korea, by the Korea Astronomy and Space Science Institute under the R&D program supervised by the Ministry of Science, ICT and Future Planning, and by the National Research Foundation of Korea (2016M1A3A3A02017017). The work at the New Jersey Institute of Technology was supported by the NASA Van Allen Probes RBSPICE instrument project provided by JHU/APL subcontract 131803 under NASA prime contract NNN06AA01C. The Van Allen Probes data used for this paper can be obtained from NASA’s CDAWeb FTP server, ftp://cdaweb.gsfc.nasa.gov, and from the EMFISIS website for the magnetic field data at http://emfisis. physics.uiowa.edu/, plasma density data at http://www.space.umn.edu/, and proton flux data from ECT-HOPE at https://rbsp-ect.lanl.gov/data_pub/ and those from RBSPICE at http://rbspicea. ftecs.com/. The data shown in Figure 9 is theoretical and can be obtained by solving equation (10) based on the method described in detail in the main text of section 5. The authors are grateful to C. A. Keltzing and Sheng Tian for checking the quality of the magnetic and electric field data. S. Noh is grateful to K. Min and L. W. Blum for their useful comments on the present work.
Funding Information:
This research at Chungbuk National University was supported by the National Meteorological Satellite Center of Korea, by the Korea Astronomy and Space Science Institute under the R&D program supervised by the Ministry of Science, ICT and Future Planning, and by the National Research Foundation of Korea (2016M1A3A3A02017017). The work at the New Jersey Institute of Technology was supported by the NASA Van Allen Probes RBSPICE instrument project provided by JHU/APL subcontract 131803 under NASA prime contract NNN06AA01C. The Van Allen Probes data used for this paper can be obtained from NASA's CDAWeb FTP server, ftp://cdaweb.gsfc.nasa.gov, and from the EMFISIS website for the magnetic field data at http://emfisis.physics.uiowa.edu/, plasma density data at http://www.space.umn.edu/, and proton flux data from ECT-HOPE at https://rbsp-ect.lanl.gov/data_pub/ and those from RBSPICE at http://rbspicea.ftecs.com/. The data shown in Figure 9 is theoretical and can be obtained by solving equation based on the method described in detail in the main text of section 5. The authors are grateful to C. A. Keltzing and Sheng Tian for checking the quality of the magnetic and electric field data. S. Noh is grateful to K. Min and L. W. Blum for their useful comments on the present work.
Publisher Copyright:
©2018. American Geophysical Union. All Rights Reserved.
PY - 2018/8
Y1 - 2018/8
N2 - Anisotropic velocity distributions of protons have long been considered as free energy sources for exciting electromagnetic ion cyclotron (EMIC) waves in the Earth's magnetosphere. Here we rigorously calculated the proton anisotropy parameter using proton data obtained from Van Allen Probe-A observations. The calculations are performed for times during EMIC wave events (distinguishing the times immediately after and before EMIC wave onsets) and for times exhibiting no EMIC waves. We find that the anisotropy values are often larger immediately after EMIC wave onsets than the times just before EMIC wave onsets and the non-EMIC wave times. The increase in anisotropy immediately after the EMIC wave onsets is rather small but discernible, such that the average increase is by ~15% relative to the anisotropy values during the non-EMIC wave times and ~8% compared to those just before the EMIC wave onsets. Based on the calculated anisotropy values, we test the criterion for ion cyclotron instability suggested by Kennel and Petschek (1966, https://doi.org/10.1029/JZ071i001p00001) by applying it to the EMIC wave events. We find that despite the weak increase in anisotropy, the majority of the EMIC wave events satisfy the instability criterion. We suggest that the proton distributions often remain close to the marginal state to ion cyclotron instability, and consequently, the proton anisotropy values should often be observed near threshold values for ion cyclotron instability. Additionally, we demonstrate the usefulness and limitation of the instability criteria expressed in the form of an inverse relation between the anisotropy and plasma beta.
AB - Anisotropic velocity distributions of protons have long been considered as free energy sources for exciting electromagnetic ion cyclotron (EMIC) waves in the Earth's magnetosphere. Here we rigorously calculated the proton anisotropy parameter using proton data obtained from Van Allen Probe-A observations. The calculations are performed for times during EMIC wave events (distinguishing the times immediately after and before EMIC wave onsets) and for times exhibiting no EMIC waves. We find that the anisotropy values are often larger immediately after EMIC wave onsets than the times just before EMIC wave onsets and the non-EMIC wave times. The increase in anisotropy immediately after the EMIC wave onsets is rather small but discernible, such that the average increase is by ~15% relative to the anisotropy values during the non-EMIC wave times and ~8% compared to those just before the EMIC wave onsets. Based on the calculated anisotropy values, we test the criterion for ion cyclotron instability suggested by Kennel and Petschek (1966, https://doi.org/10.1029/JZ071i001p00001) by applying it to the EMIC wave events. We find that despite the weak increase in anisotropy, the majority of the EMIC wave events satisfy the instability criterion. We suggest that the proton distributions often remain close to the marginal state to ion cyclotron instability, and consequently, the proton anisotropy values should often be observed near threshold values for ion cyclotron instability. Additionally, we demonstrate the usefulness and limitation of the instability criteria expressed in the form of an inverse relation between the anisotropy and plasma beta.
KW - EMIC waves
KW - RBSP
KW - Van Allen Probes
KW - ion cyclotron instability
KW - temperature anisotropy
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U2 - 10.1029/2018JA025385
DO - 10.1029/2018JA025385
M3 - Article
AN - SCOPUS:85052388436
SN - 2169-9380
VL - 123
SP - 6591
EP - 6610
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
IS - 8
ER -