Two-dimensional ionospheric electrodynamics of auroral disturbances are studied with high time resolution using the Advanced Modular Incoherent Scatter Radar (AMISR) at the Poker Flat Rocket Range in Alaska. The electrodynamics associated with the nighttime electric field reversal (known as the Harang discontinuity) and with the temporal evolution of polar-cap convection strength are specific observation targets, and the primary research objective is to understand the physics governing large-scale plasma sheet transport and the electrodynamic coupling of that transport to the ionosphere. Magnetic substorm onsets, substorm growth phase auroral arcs, dynamic pressure disturbances, and auroral poleward boundary intensifications - all of which couple to plasma sheet convection, are included as observational targets of interest for which the electrodynamics of formation, evolution, and decay are established and compared to current substorm theory. In addition, the electrodynamics associated with aurora caused by Alfvenic wave electron acceleration are contrasted with the aurora triggered by static field-aligned potential drops (Inverted-V aurora). The AMISR measurements are placed into a larger regional context of auroral evolution by use of data from optical imagers and magnetometers in Alaska. The strength and evolution of convection in the polar cap is determined using simultaneous measurements from AMISR, the Sondrestromfjord incoherent scatter radar, and the EISCAT Svalbard incoherent scatter radar.
The highly varying structure and dynamics of the near-Earth space (geospace) environment, including the energetic charged particles and fields within the magnetosphere and the ionosphere, substantially affect man-made space systems and susceptible ground systems. Unlike that of tropospheric weather, Space Weather dynamics and disturbances have remained poorly understood because of complicated magnetosphere-ionosphere coupling and limitations on capabilities for measuring and modeling the coupled system. However, the opportunity to dramatically change this situation is now emerging due to NSF deployments of new and expanded radar systems, the ground auroral imaging and multi-spacecraft of the NASA THEMIS program. We have performed some Initial studies that have suggested that these new capabilities may lead to a new and transformational view of geospace dynamical processes. As an example, we discovered a previously unknown basic mode of energy transfer from the solar wind to the Earth's magnetosphere. (See also UCLA press release (http://newsroom.ucla.edu/portal/ucla/scientists-discover-surprise-in-101025.aspx). The sun, in addition to emitting radiation, emits a stream of ionized particles called the solar wind that affects the Earth and other planets in the solar system. The solar wind, which carries the particles from the sun's magnetic field, known as the interplanetary magnetic field, takes about three or four days to reach the Earth. When the charged electrical particles approach the Earth, they carve out a highly magnetized region — the magnetosphere — which surrounds and protects the Earth. Charged particles carry currents, which cause significant modifications in the Earth's magnetosphere. This region is where communications spacecraft operate and where the energy releases in space known as substorms wreak havoc on satellites, power grids and communications systems. The rate at which the solar wind transfers energy to the magnetosphere can vary widely, but what determines the rate of energy transfer is unclear. We thought it was known, but we came up with a major surprise. We all have thought for our entire careers that the closer to southward-pointing is the solar magnetic field reaching the Earth, and the stronger the magnetic field is in that direction, the stronger is the energy transfer rate. If it is both southward and big, the energy transfer rate is even bigger. We found that generally this is correct, but when you have a fluctuating magnetic field, the transfer of energy to the magnetosphere and ionosphere can be strong, independent of the direction of the interplanetary magnetic field. This indicates that there is a important process for the transfer of solar wind energy to the Earth’s magnetosphere-ionosphere system and upper atmosphere that has not been previously identified and that requires understanding. We also found that colliding auroras can produce an explosion of light that is referred to as a substorm (http://newsroom.ucla.edu/portal/ucla/colliding-auroras-produce-an-explosion-150031.aspx). The substorm is a major Space Weather disturbance that can have damaging effects on man-made electrical systems in space and on the ground, but understanding of substorm physics has been an illusive and controversial topic for the past several decades. We also found supporting evidence for how the collision process works using observations form National Science Foundation radars and NASA spacecraft. Furthermore, taking advantage of the radars and complementary ground-based instruments and auroral observations, graduate student Shasha Zou, in collaboration with others in our research group at UCLA, obtained fundamental new understand of the electrodynamics properties of the substorm. It was found that the auroral activity at substorm onset is located in the center of a flow shear region called the Harang reversal. This flow reversal is a key region in the ionosphere and magnetosphere and is a central part of the Region 2 electrical current system that connects the magnetosphere and ionosphere. The radar observations have also shown that flows exhibit repeatable distinct variations at different locations relative to that of the substorm-related auroral activity. This has provided a 2-D picture of the important features of the substorm process and has for the first time revealed a close relationship between the substorm and the Region 2 currents. We our proud that Dr. Zou was awarded the prestigious Scarf Award from the American Geophysical Union for her research on this topic while a graduate student.
