Storm Time EMIC Waves Observed by Swarm and Van Allen Probe Satellites

<p>The temporal and spatial evolution of electromagnetic ion cyclotron (EMIC) waves during<br>the magnetic storm of 21–29 June 2015 was investigated using high-resolution magnetic field observations<br>from Swarm constellation in the ionosphere and Van Allen Probes in the magnetosphere. Magnetospheric<br>EMIC waves had a maximum occurrence frequency in the afternoon sector and shifted equatorward during<br>the expansion phase and poleward during the recovery phase. However, ionospheric waves in subauroral<br>regions occurred more frequently in the nighttime than during the day and exhibited less obvious<br>latitudinal movements. During the main phase, dayside EMIC waves occurred in both the ionosphere<br>and magnetosphere in response to the dramatic increase in the solar wind dynamic pressure. Waves were<br>absent in the magnetosphere and ionosphere around the minimum SYM-H. During the early recovery<br>phase, He<sup>+ </sup>band EMIC waves were observed in the ionosphere and magnetosphere. During the late<br>recovery phase, H<sup>+</sup> band EMIC waves emerged in response to enhanced earthward convection during<br>substorms in the premidnight sector. The occurrence of EMIC waves in the noon sector was affected by<br>the intensity of substorm activity. Both ionospheric wave frequency and power were higher in the summer<br>hemisphere than in the winter hemisphere. Waves were confined to an MLT interval of less than 5 hr with a<br>duration of less than 186 min from coordinated observations. The results could provide additional insights<br>into the spatial characteristics and propagation features of EMIC waves during storm periods</p>