Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B


Dayside magnetospheric and ionospheric responses to transient upstream disturbances measured by satellite-imager coordination


Boyi Wang

Geophysical Institute, UAF



The transient upstream disturbances, including foreshock transients and magnetosheath high-speed jets (HSJs), can create dramatic dynamic pressure variation near the magnetopause and generate significant ultra-low frequency (ULF) waves, during the absent of solar wind dynamic pressure variation. However, how do those disturbances in the foreshock region and magnetosheath impact the coupled magnetospheric and ionospheric system is still poorly understood. This study presents a comprehensive analysis of the M-I responses to foreshock transients and magnetosheath HSJs, by coordinate observation between the THEMIS satellites, ground-based magnetometers and imagers at South Pole. Compared to the sparse distribution of the in situ observation in the magnetosphere, the ground-based measurements have an advantage of identifying the shape and evolution of the localized and transient disturbances in 2-D perspective. The observation shows that foreshock transients and magnetosheath HSJs are able to drive magnetospheric Pc5-band (150-600s) ULF waves, including both compressional waves and field line resonances (FLRs). Those magnetospheric signatures are likely in the same manner as interplanetary shocks but with a localized dawn-dusk extent in the dayside magnetosphere. In some cases, the foreshock-driven compressional waves propagated to midnight as observed by ground-based magnetometers. In optical images, we found that both discrete and diffuse aurora brighten locally and periodically as modulated by the upstream-driven compressional Pc5 waves. Besides, the periodical poleward moving east-west arcs occurred with the FLRs which were driven by the upstream transients. The 2-D imaging further allows to measure azimuthal distribution, especially the azimuthal wavenumber, of the FLRs in the magnetosphere and their north-south width in the ionosphere. The high-resolution optical imagers are also used to identify a high-wavenumber mode wave, which probably coupled with the low-wavenumber FLRs.


Friday, 1 Nov. 2019

Globe Room, Elvey Building