Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B


Dayside magnetosphere and ionosphere responses to transient upstream disturbances measured by satellite-imager coordination

Boyi Wang



Dayside aurora reflects magnetospheric responses to upstream disturbances, and imaging allows to perform remote sensing of solar wind-magnetosphere interaction. Auroral responses include poleward moving aurora forms (PMAFs), which are considered as an ionospheric signature of transient dayside reconnection and flux transfer events (FTEs); and shock aurora as brightening of discrete and diffuse aurora as the response to solar wind dynamic pressure pulses. Recently, foreshock disturbances and magnetosheath high-speed jets (HSJs) were also found geoeffective, and ionospheric measurements have a potential to identify 2-d evolution of their interaction to the magnetosphere. In our previous work, the conjunction between Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites and the all-sky- imagers (ASIs) of the Automatic Geophysical Observatories (AGOs) revealed the probability of PMAF triggering by solar wind. It shows that the southward turnings of interplanetary magnetic field (IMF) plays an important role in triggering PMAFs. Furthermore, the conjunction between the Defense Meteorological Satellite Program (DMSP) satellites and the ASIs of the AGOs is utilized to study the evolution of PMAFs in the polar cap. PMAFs are found to evolve to polar cap airglow patches, associated with meso-scale antisunward fast flows, which have an average width of ~300 km and an average speed of ~1100 m/s. Besides, similar to shock aurora, localized and transient disturbances, including foreshock transients and magnetosheath high-speed jets (HSJs), which compress the magnetosphere locally, also brighten the dayside diffuse except for a smaller scale. HSJs are transient but significant dynamic pressure impulses in the magnetosheath in an absent of solar wind compression. Our current work for the first time shows the discrete/diffuse aurora responses to HSJs. The conjunction between THEMIS satellites and the ASI at South Pole help to measure the shape and the evolution of the HSJs in 2-D perspective. It is found that the azimuthal size of HSJ-related diffuse aurora signatures is ~800 km at 230 km altitude in the ionosphere and ~3.7 Re in the magnetosphere, which is slightly larger but of the order of the cross-sectional diameter of HSJs (~1 Re). Besides of magnetosheath HSJs, diffuse aurora also reflect the motion of foreshock transients. The mapped pattern of the corresponding diffuse aurora brightening in the equatorial plane shows a width of ~4.3 Re in GSM-Y direction, which is slightly larger but similar to the typical size of foreshock transients. The average velocity of the mapped pattern is ~100.0 km/s in GSM-Y direction, similar as the motion of the upstream foreshock transient.


Friday, 9 March 2018

Globe Room, Elvey Building