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EMIC waves observed at geosynchronous orbit under quiet geomagnetic conditions ( Kp ≤ 1)
Author(s) -
Park J.S.,
Kim K.H.,
Shiokawa K.,
Lee D.H.,
Lee E.,
Kwon H.J.,
Jin H.,
Jee G.
Publication year - 2016
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021968
Subject(s) - geosynchronous orbit , physics , solar wind , emic and etic , local time , geophysics , van allen probes , geomagnetic storm , earth's magnetic field , magnetosphere , dynamic pressure , interplanetary magnetic field , ring current , quiet , computational physics , astrophysics , geodesy , atmospheric sciences , geology , astronomy , magnetic field , van allen radiation belt , mechanics , satellite , quantum mechanics , mathematics , statistics , sociology , anthropology
We statistically study the local time distribution of the helium band electromagnetic ion cyclotron (EMIC) waves observed at geosynchronous orbit when geomagnetic activity was low ( K p ≤ 1). In order to identify the geosynchronous EMIC waves, we use high time resolution magnetic field data acquired from GOES 10, 11, and 12 over a 2 year period from 2007 and 2008 and examine the local time distribution of EMIC wave events. Unlike previous studies, which reported high EMIC wave occurrence in the postnoon sector with a peak around 1500–1600 magnetic local time (MLT) during magnetically disturbed times (i.e., storm and/or substorm), we observed that quiet time EMIC waves mostly occur in a region from morning (∼0600 MLT) to afternoon (∼1600 MLT) with a peak around 1100–1200 MLT. To investigate whether the quiet time EMIC wave occurrence has a causal relationship with magnetospheric convection enhancement or solar wind dynamic pressure variations, we performed a superposed epoch analysis of solar wind parameters (solar wind speed, density, dynamic pressure, and interplanetary magnetic field B z ) and geomagnetic indices ( A E and S Y M ‐ H ). From the superposed epoch analysis we found that solar wind dynamic pressure variation is a more important parameter than A E and S Y M ‐ H for quiet time EMIC wave occurrence.