17:15 〜 19:15
[PEM13-P14] Statistical properties of the distribution of EMIC waves in the magnetosphere observed by Cluster satellite in 2011-2022
キーワード：EMIC波動、統計解析、Cluster衛星
Electromagnetic ion cyclotron (EMIC) waves are left-hand polarized plasma waves that propagate in the frequency range below the proton gyrofrequency. These waves are known to play a significant role in wave-particle interactions in the Earth's magnetosphere, leading to the precipitation of radiation belt electrons and ring current ions into the atmosphere. Understanding the generation mechanisms, propagation characteristics, and spatial distribution of EMIC waves is crucial for an understanding of magnetospheric dynamics and space weather phenomena.
Previous statistical studies of EMIC waves using Cluster data have been performed in the period from 2001 to 2010(Allen+ 2015,2016). We extend the analysis to the period from 2011 to 2022 to investigate the statistical properties of EMIC waves in different solar cycles. The period from 2011 onwards corresponds to solar cycle 24, whose solar activities were weaker than those in solar cycle 23. Furthermore, since the Cluster's orbital coverage has changed since the earlier studies, extending the statistical analysis to the period of 2011-2022 is expected to yield new insights into EMIC wave characteristics under different solar activity levels and spatial coverage. The Cluster’s polar orbit provides a unique advantage, enabling us to investigate EMIC wave properties at higher latitudes and throughout a wider range of L-shell.
In the present study, we show statistical distribution on the occurrence probability, spatial distribution, and polarization characteristics of EMIC waves in the magnetosphere observed by Cluster in the period of 2011-2022. We analyze the dataset covering the range of magnetic latitude up to 60 degrees and L-values up to 15. The nearly dipolar inner magnetosphere (L < 6) is almost equally covered for all MLTs. However, the middle to outer magnetosphere (L > 6) is strongly affected by magnetospheric compression and stretching, resulting in asymmetric dwell times. This asymmetry in Cluster dwell times covers the day side magnetosphere well but is insufficient for a statistical analysis of most of the midnight side outer magnetosphere. We investigate the dependence of EMIC wave occurrence and properties on solar activity indices, geomagnetic indices, and solar wind parameters (e.g., solar wind speed, interplanetary magnetic field). By comparing our results with previous statistical studies based om the Cluster and Arase satellite observations, we aim to provide a more comprehensive understanding of EMIC wave behavior in the Earth's magnetosphere.
Previous statistical studies of EMIC waves using Cluster data have been performed in the period from 2001 to 2010(Allen+ 2015,2016). We extend the analysis to the period from 2011 to 2022 to investigate the statistical properties of EMIC waves in different solar cycles. The period from 2011 onwards corresponds to solar cycle 24, whose solar activities were weaker than those in solar cycle 23. Furthermore, since the Cluster's orbital coverage has changed since the earlier studies, extending the statistical analysis to the period of 2011-2022 is expected to yield new insights into EMIC wave characteristics under different solar activity levels and spatial coverage. The Cluster’s polar orbit provides a unique advantage, enabling us to investigate EMIC wave properties at higher latitudes and throughout a wider range of L-shell.
In the present study, we show statistical distribution on the occurrence probability, spatial distribution, and polarization characteristics of EMIC waves in the magnetosphere observed by Cluster in the period of 2011-2022. We analyze the dataset covering the range of magnetic latitude up to 60 degrees and L-values up to 15. The nearly dipolar inner magnetosphere (L < 6) is almost equally covered for all MLTs. However, the middle to outer magnetosphere (L > 6) is strongly affected by magnetospheric compression and stretching, resulting in asymmetric dwell times. This asymmetry in Cluster dwell times covers the day side magnetosphere well but is insufficient for a statistical analysis of most of the midnight side outer magnetosphere. We investigate the dependence of EMIC wave occurrence and properties on solar activity indices, geomagnetic indices, and solar wind parameters (e.g., solar wind speed, interplanetary magnetic field). By comparing our results with previous statistical studies based om the Cluster and Arase satellite observations, we aim to provide a more comprehensive understanding of EMIC wave behavior in the Earth's magnetosphere.