Journal
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
Volume 121, Issue 2, Pages 1377-1390Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2015JA021968
Keywords
EMIC waves; geosynchronous orbit; solar wind dynamic pressure
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Funding
- BK21+ through the National Research Foundation (NRF) - Ministry of Education of Korea
- Basic Science Research Program through NRF [NRF-2013R1A1A2A10004414]
- Korea Polar Research Institute [PE15090]
- JSPS KAKENHI [15H05815]
- Korea Institute of Marine Science & Technology Promotion (KIMST) [PE15090] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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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 (Kp 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 2year 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 (approximate to 0600MLT) to afternoon (approximate to 1600MLT) with a peak around 1100-1200MLT. 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 (AE and SYM-H). From the superposed epoch analysis we found that solar wind dynamic pressure variation is a more important parameter than AE and SYM-H for quiet time EMIC wave occurrence.
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