UCLA

This dissertation presents a comprehensive study of the dayside auroral dynamics and remote sensing of coupled magnetosphere-ionosphere system responses to various upstream disturbances, which include interplanetary magnetic field (IMF) discontinuities, foreshock transients, and magnetosheath high speed jets (HSJs). Recent studies have shown that these disturbances have significant impacts on coupled magnetosphere-ionosphere system, changing the particle transportation and energy budget. However, it has been difficult to find spatial structure and evolution of the interaction processes using a limited number of in-situ measurements. This dissertation aims to understand how dayside aurora and airglow respond to upstream disturbances, and to utilize auroral imaging to determine how the magnetosphere-ionosphere system responds to the upstream disturbances. Our study takes a unique approach by taking advantage of high-resolution 2D imaging to vastly increase community's understanding of magnetosphere-ionosphere responses to upstream disturbances, through tracing location, size and propagation of optical structures.

We first examine the role of IMF southward turnings as the trigger of Poleward Moving Auroral Forms (PMAFs), which are thought to be an ionospheric signature of dayside magnetic reconnection. While PMAFs are more likely to occur when the IMF is southward, how often PMAFs are triggered by changes in solar wind parameters is still a major open question and has only been poorly understood due to the use of solar wind monitors far away from the bow shock. This dissertation addresses this question with the conjunction between the all-sky imager (ASI) at Automatic Geophysical Observatories (AGO) P1 station in Antarctica and the Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and C satellites, which provide much more accurate solar wind conditions than the solar wind monitors at the L1 point. In a statistical study using 60 PMAF events, 70% of the events show a reduction of IMF Bz before PMAF onset, which indicates that IMF southward turning plays an important role in triggering a majority of PMAFs.

Those PMAFs were further found to evolve to polar cap airglow patches. This dissertation investigates how often polar cap patches originate in PMAFs and are associated with flow channels, using the conjunction between the ASI at the AGO P1 station and DMSP satellites. Our 50-event statistical study shows that in a majority (45) of events, longitudinally narrow flow enhancements directed anti-sunward are found to be collocated with the patches, have velocities (up to a few km/s) substantially larger than the large-scale background flows (~500 m/s) and have widths comparable to patch widths (~400 km). The patches emanated out of PMAFs and were found to have a large IMF By dependence on the MLT of patches entering the polar cap.

Through investigation of dayside aurora, we noticed that auroral brightenings can occur even without substantial changes in the IMF Bz or dynamic pressure. We examined whether disturbances generated in the foreshock and magnetosheath can contribute to dayside auroral brightening. Studies of the impact of foreshock and magnetosheath transients on the magnetosphere-ionosphere system are very limited, and it has been difficult to find how the transients interact in individual events due to limited in-situ and space-based imaging observations. In this dissertation, the conjunction between the ASI at South Pole and the THEMIS satellites during 2008 through 2011 is utilized to determine the magnetosphere-ionosphere responses to foreshock transients and magnetosheath HSJs in a 2D perspective.

In situ observation by the THEMIS satellites showed that a foreshock transient during 1535–1545 UT on 25 June 2008 was associated with magnetospheric compression. The ASI at South Pole observed that both diffuse and discrete aurora brightened locally soon after the appearance of this foreshock transient. With the advantage of the high-resolution 2D imaging, we were able to determine that the diffuse auroral brightening corresponds to a localized azimuthal extent of a few Re size on the equatorial plane, and propagated duskward with an average speed of ~100 km/s. Similarly, we for the first time show a nearly one-to-one relationship between the HSJs and individual localized discrete/diffuse auroral brightenings using eight HSJ events. The azimuthal size of HSJ-related diffuse auroral 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). Furthermore, most of those auroral signatures have azimuthal motions, whose magnitude and direction agree with magnetosheath background flows.

In addition to magnetospheric compression, foreshock transients were also found to cause Pc5-band (150-600s) ultra-low frequency (ULF) waves, which are important in transporting mass, energy and momentum in the coupled magnetosphere-ionosphere system. Although it is difficult to find spatial structure of dayside Pc5 waves by a small number of satellites or ground magnetometers, we have successfully determined the 2D structure and motion of ULF waves in the ionosphere using optical imagers. This dissertation reports two series of foreshock-driven Pc5 waves, which are found to be field line resonances (FLRs). The ground-based ASI at South Pole shows that periodic poleward moving east-west arcs are the ionospheric signature of FLRs. The azimuthal distribution, including dawn-dusk symmetricity and azimuthal wavenumbers, of the FLRs in the magnetosphere, are further determined by 2D imaging. The fine structure embedded in the large-scale arcs indicates a wave with high toroidal wavenumber (m ~ 140) was coupled with the FLRs. Based on these works, a likely scenario revealed from the satellite-imaging coordinated observations is as follows: Foreshock transients and magnetosheath HSJs drive compressions of the magnetopause at a few RE, much more localized than global compression by shocks. The compressions launch fast-mode waves and FLRs, which create localized electron precipitation and auroral brightenings. The auroral responses found in this study can highlight structure and evolution of the magnetospheric and ionospheric responses, and signify the geoeffectiveness of localized and transient upstream energy input.