Home » Kim and Shprits 2018

Survey of the Favorable Conditions for Magnetosonic Wave Excitation

Kim K., Y. Shprits, (2018), Survey of the Favorable Conditions for Magnetosonic Wave Excitation, J. of Geophys. Res. [Space Physics], 123, 400-413, doi:10.1002/2017JA024865

Abstract

Abstract The ratio of the proton ring velocity (VR) to the local Alfven speed (VA), in addition to proton ring distributions, plays a key factor in the excitation of magnetosonic waves at frequencies between the proton cyclotron frequency fcp and the lower hybrid resonance frequency fLHR in the Earth's magnetosphere. Here we investigate whether there is a statistically significant relationship between occurrences of proton rings and magnetosonic waves both outside and inside the plasmapause using particle and wave data from Van Allen Probe-A during the time period of October 2012 to December 2015. We also perform a statistical survey of the ratio of the ring energy (ER, corresponding to VR) to the Alfven energy (EA, corresponding to VA) to determine the favorable conditions under which magnetosonic waves in each of two frequency bands (fcp < f ≤ 0.5 fLHR and 0.5 fLHR < f < fLHR) can be excited. The results show that the magnetosonic waves in both frequency bands occur around the postnoon (12–18 magnetic local time, MLT) sector outside the plasmapause when ER is comparable to or lower than EA, and those in lower-frequency bands (fcp < f ≤ 0.5 fLHR) occur around the postnoon sector inside the plasmapause when ER/EA > ~9. However, there is one discrepancy between occurrences of proton rings and magnetosonic waves in low-frequency bands around the prenoon sector (6–12 MLT) outside the plasmapause, which suggests either that the waves may have propagated during active time from the postnoon sector after being excited during quiet time, or they may have locally excited in the prenoon sector during active time.

Authors (sorted by name)

Kim Shprits

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Acknowledgments

This research was supported by the Daegu University Research grant 20160376. We thank the GSFC/SPDF OMNIWeb for the provision of AE index used in this report. The Van Allen Probe data are available from http://emfisis.physics.uiowa.edu/Flight and from https://rbsp‐ect.lanl.gov/data_pub/rbspa. We graciously thank the Van Allen Probes team, especially the EMFISIS and ECT teams. The electron number density derived by Neural‐network‐based Upper hybrid Resonance Determination algorithm for the Van Allen Probes is available from ftp://rbm.epss.ucla.edu/ftpdisk1/NURD.

Bibtex

@article{doi:10.1002/2017JA024865,
author = {Kim, Kyung-Chan and Shprits, Yuri},
title = {Survey of the Favorable Conditions for Magnetosonic Wave Excitation},
journal = {Journal of Geophysical Research: Space Physics},
year = {2018},
volume = {123},
number = {1},
pages = {400-413},
keywords = {magnetosonic equatorial noise, proton ring distribution, Van Allen Probes},
doi = {10.1002/2017JA024865},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017JA024865},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017JA024865},
abstract = {Abstract The ratio of the proton ring velocity (VR) to the local Alfven speed (VA), in addition to proton ring distributions, plays a key factor in the excitation of magnetosonic waves at frequencies between the proton cyclotron frequency fcp and the lower hybrid resonance frequency fLHR in the Earth's magnetosphere. Here we investigate whether there is a statistically significant relationship between occurrences of proton rings and magnetosonic waves both outside and inside the plasmapause using particle and wave data from Van Allen Probe-A during the time period of October 2012 to December 2015. We also perform a statistical survey of the ratio of the ring energy (ER, corresponding to VR) to the Alfven energy (EA, corresponding to VA) to determine the favorable conditions under which magnetosonic waves in each of two frequency bands (fcp < f ≤ 0.5 fLHR and 0.5 fLHR < f < fLHR) can be excited. The results show that the magnetosonic waves in both frequency bands occur around the postnoon (12–18 magnetic local time, MLT) sector outside the plasmapause when ER is comparable to or lower than EA, and those in lower-frequency bands (fcp < f ≤ 0.5 fLHR) occur around the postnoon sector inside the plasmapause when ER/EA > ~9. However, there is one discrepancy between occurrences of proton rings and magnetosonic waves in low-frequency bands around the prenoon sector (6–12 MLT) outside the plasmapause, which suggests either that the waves may have propagated during active time from the postnoon sector after being excited during quiet time, or they may have locally excited in the prenoon sector during active time.}
}