[P-EM13] [EE] Exploring space plasma processes with Magnetospheric Multiscale (MMS) mission

[PEM13-10] Global observations of high-m poloidal waves in the magnetosphere during the recovery phase of the June 2015 magnetic storm

*Guan Le¹, Peter Chi², Robert J Strangeway², Christopher T Russell², James Slavin³, Kazue Takahashi⁴, Howard Singer⁵, Vassilis Angelopoulos², Brain Anderson⁴, Kenneth Bromund¹, David Fischer⁶, Emil Kepko¹, Werner Magnes⁶, Rumi Nakamura⁶, Ferdinand Plaschke⁶, Roy Torbert⁷ (1.NASA Goddard Space Flight Center, USA, 2.University of California, Los Angeles, USA, 3.University of Michigan, USA, 4.The Johns Hopkins University Applied Physics Laboratory, USA, 5.National Oceanic and Atmospheric Administration/SEC, USA, 6.Space Reserach Institute, Austrian Academy of Sciences, Austria, 7.University of New Hampshire, USA )

Keywords:Magnetospheric ULF Waves, High-m Poloidal Waves, Magnetospheric Multiscale Mission, Magnetic Storms

In this paper, we report global observations of high-m poloidal waves occurred during the recovery phase of the magnetic storm starting on 22 June 2015. The long lasting waves are observed by a constellation of widely spaced satellites from 5 missions including MMS, Van Allen Probes, THEMIS, Cluster, and GOES, covering L-values between 4 and 12 in a large range of local times. These observations have demonstrated that storm-time high-m poloidal waves can occur globally. High-resolution data from four MMS satellites enable us to detect the azimuthal phase shifts and determine the m number to be ∼ 100. The mode identification suggests that the observed poloidal waves are associated with the second harmonic of the field line resonance. The wave frequencies range from 8 to 22 mHz and decrease as the L-value increases. Detailed examinations of instantaneous wave frequency show discrete spatial structures with step-like changes along the radial direction. In each discrete structure the wave has a steady frequency and spans about 1 Re in the radial direction. Our observations suggest that storm-time high-m poloidal waves are different from the single-frequency global poloidal mode waves that are common during periods of low-level of geomagnetic activities.