Research over the past few years has demonstrated for the first time that there are several fundamentally different types of geomagnetic disturbances having time scales ranging from a few minutes to a few hours and ground magnetic field perturbations ranging from a few tens of nT to ~2000 nT. Each has unique characteristics, reflects distinctly different physical processes occurring within the magnetosphere, and contributes significantly to overall space weather activity that affects manmade systems in space and on the ground. The general objective of the research proposed here is to determine important aspects of the two- dimensional structure and temporal dynamics of these different disturbances by using the recently enhanced capabilities for Arctic ground-based observations (CANOPUS, NORSTAR, SuperDARN) of currents, electric fields, and optical emissions within the auroral ionosphere, in combination with appropriate spacecraft observations (DMSP, POLAR, IMAGE, LANL, GOES, Geotail). Specific objectives related to the following disturbances include:
Poleward boundary intensifications (PBIs: have an auroral signature that can extent equatorward from the poleward boundary of the auroral oval and are associated with short- time scale flow bursts in the magnetotail): Determine the two-dimensional structure of PBIs, and when and where their different types of two-dimensional structure occur. Relate the local two-dimensional structure to global auroral structure. Investigate the possibility that PBIs are a manifestation of a global magnetospheric oscillation by determining whether PBIs generally show large power at auroral-zone ULF frequencies, if the same ULF frequencies seen in the auroral oval are simultaneously seen in the nightside plasma sheet, and if consistent phase speeds can be seen for PBI-related variations. Determine if PBIs extending to low latitudes are of such large scale that they simultaneously affect the nightside plasmasheet from x ~ -30 RE (or near the separatrix) to synchronous orbit. Determine the two-dimensional relation between PBIs and plasma flows in the auroral ionosphere.
Dynamic pressure disturbances (large and rapid brightening, broadening, and poleward expansion of the auroral oval caused by enhancements in solar wind dynamic pressure): Determine (a) whether reconnection and the amount of open magnetic flux over the polar caps is in general strongly controlled by the dynamic pressure of the solar wind as recent observations suggest, (b) whether the strength of ionospheric and region 1 currents are strongly controlled by solar wind dynamic pressure, and (c) how convection electric fields and the cross-polar cap potential drop depend upon dynamic pressure.
Convection-driven morningside auroral disturbances (auroral enhancements at midnight to dawn MLTs that occur during prolonged periods of enhance convection): Identify the current (ionospheric and field aligned), electric field, and precipitation particle characteristics directly associated with these dawnside auroral enhancements.
Substorms: Obtain an answer to the critical question of whether closer to 50% or closer to 100% of substorms are triggered by IMF changes that lead to a reduction in large- scale convection. This will be accomplished using the recently enhanced SuperDARN radar network to determine whether reductions in the strength of polar-cap convection (which must be related to appropriate IMF changes) are directly associated with substorm onset, and whether, for a given amount of energy stored in the tail, the strength of a substorm expansion phase is proportional to the amount of reduction in the strength of convection.
