SM41H-2577
Statistical analysis of plasmaspheric magnetosonic mode waves from Van Allen Probes observations
Thursday, 17 December 2015
Poster Hall (Moscone South)
Koji Nomura1, Yoshizumi Miyoshi1, Kunihiro Keika1, Masafumi Shoji2, Satoshi Kurita1, Naritoshi Kitamura3, Shinobu Machida1, Ondrej Santolik4, Craig Kletzing5 and Scott A Boardsen6, (1)Nagoya University, Nagoya, Japan, (2)Nagoya University, Solar-Terrestrial Environment Laboratory, Nagoya, Japan, (3)ISAS Institute of Space and Astronautical Science, JAXA Japan Aerospace Exploration Agency, Kanagawa, Japan, (4)Institute of Atmospheric Physics ACSR, Praha 4, Czech Republic, (5)University of Iowa, Iowa City, IA, United States, (6)NASA Goddard Space Flight Center, Heliophysics Science Division, Greenbelt, MD, United States
Abstract:
Magnetosonic waves (MSWs) are electromagnetic emissions whose properites can be described by the cold plasma extraordinary mode, which are typically generated at frequencies (f) between the proton cyclotron frequency (fcp) and the lower hybrid resonant frequency. It has been suggested that MSWs can contribute to the acceleration of relativistic electrons in the radiation belts. In this study, we investigate the Poynting vector of plasmaspheric MSWs using the spectral matrix data from the EMFISIS instrument onboard the Van Allen Probes spacecraft. We derived the polarization and planarity from the spectrum matrix using the SVD method (Santolik et al., 2003) and also estimated the Poynting vector. The planarity is used as a proxy to distinguish presence of a single wave vector from mixture of waves propagating in different directions. The Poynting vector of MSWs with high planarity shows that the MSWs are observed to propagate radially as well as longitudinally. The occurrence probability of the propagation directions depends on the geomagnetic activities. During the geomagnetically quiet periods　(Kp < 3), the percentage of inward, outward, and longitudinal propagations of MSWs at 60 Hz are 22%, 36% and 42% respectively. On the other hand, during the geomagnetically active periods (Kp > 5), the percentages are 53%, 21%, and 26%, respectively. The result indicates that the MSWs tend to propagate inward during the geomagnetically active periods. Since the fundamental frequency of the ion Bernstein mode would be local cyclotron frequency, we also investigate the source of MSWs from the minimum frequency of MSWs. It is found that a large number of MSWs tend to be generated at L=3.0-3.5 inside the plasmapause. We will also discuss the validity of the Poynting flux computation as a function of f/fcp.
