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Survey of the Favorable Conditions for Magnetosonic Wave Excitation
Author(s) -
Kim KyungChan,
Shprits Yuri
Publication year - 2018
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2017ja024865
Subject(s) - plasmasphere , physics , magnetosphere , ring current , proton , excitation , atomic physics , van allen probes , excited state , very low frequency , cyclotron , computational physics , plasma , nuclear physics , van allen radiation belt , quantum mechanics , astronomy
The ratio of the proton ring velocity ( V R ) to the local Alfven speed ( V A ), in addition to proton ring distributions, plays a key factor in the excitation of magnetosonic waves at frequencies between the proton cyclotron frequency f cp and the lower hybrid resonance frequency f LHR 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 ( E R , corresponding to V R ) to the Alfven energy ( E A , corresponding to V A ) to determine the favorable conditions under which magnetosonic waves in each of two frequency bands ( f cp < f ≤ 0.5 f LHR and 0.5 f LHR < f < f LHR ) 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 E R is comparable to or lower than E A , and those in lower‐frequency bands ( f cp < f ≤ 0.5 f LHR ) occur around the postnoon sector inside the plasmapause when E R / E A > ~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.