This project will study the influence of solar wind conditions on isolated high-latitude transpolar arcs (also known as theta aurora) and determine the local and global plasma flows in the ionosphere associated with the arcs. The project will examine the electrodynamic characteristics of the transpolar arcs and relate them to the corresponding A total of 87 events where Defense Meteorological Satellite Program (DMSP) F13 satellite has measured precipitating charged particles associated with transpolar arcs. The satellite measurements will be used to determine: (1) the spatial extent of the precipitating particle regions, (2) the electrostatic potential distribution, (3) the cross-track (sunward/antisunward) horizontal ionospheric plasma flow, (4) precipitating ion and electron average energies and fluxes, and (5) field-aligned currents. In addition to the satellite measurements, data from the Super dual Auroral Radar Network (SuperDARN) will be used to determine the details of the ionospheric convection pattern associated with the transpolar arcs.
This project will examine the energy coupling between the solar wind, Earth's magnetosphere, and the ionosphere during periods when the interplanetary magnetic field (IMF) is pointing northward. During northward IMF, auroral arcs often form and divide the polar cap into two apparently separate regions. The project seeks to understand the nature of the electromagnetic coupling of the different regions and how they evolve.
The Sun plays a crucial role for life on Earth. It provides not only daylight and ultraviolet radiation causing suntans but also emits a continuous stream of charged particles, the solar wind. The Earth is surrounded by a magnetic field, which makes navigation using a compass possible, but even more importantly shields the Earth from the solar wind and other cosmic rays. The interaction that takes place when the solar wind reaches the Earth's magnetic field sets up an electric potential drop across the magnetosphere, a "bubble" separating the Earth's atmosphere from the solar wind, extending from a few hundred kilometers altitude to several tens of thousands of kilometers. Inside the magnetosphere charged particles are guided in their motion by the magnetic field. Following the magnetic field from the region where it interacts with the solar wind normally takes us to an oval-shaped area close to the arctic circles, the auroral ovals, the regions where the brightest auroral display are typically seen. The auroral emissions occur when charged particles traveling along the magnetic field at high velocity hit the atmosphere and energize the atmospheric atoms or molecules. Depending on the velocity the precipitating particles will deposit their energy at different altitudes and interact with different atmospheric particle species, which explains the varying colors of the aurora. The impinging particles have gained their energy from being accelerated by electric fields as they travel down the magnetic field lines. These electric fields are a consequence of the solar wind interaction and they are highly variable both in strength and location, explaining the dynamic nature of the auroral displays. The most active aurora typically occurs when the magnetic field carried with the solar wind is parallel to the Earth's dipole. When it is antiparallel, roughly half of the time, the aurora is normally less active, but sometimes has a very interesting topology where the optical emissions are found not only in the auroral oval but also in Sun-aligned bars at high latitudes connecting the dayside and nightside parts of the oval. These bars are called transpolar arcs and when the transpolar arc is found in the center of the auroral oval the entire auroral configuration is called theta aurora because of its resemblance of the Greek letter theta if viewed from satellite altitude. The present study focused on determining the influence on isolated high-latitude transpolar arcs of the conditions prevailing in the solar wind, determining the characteristics of the precipitating charged particle causing the aurora and, studying the speed and direction of the flow of charged particles associated with the auroral arcs. Because of the typically lower intensity of the aurora in the antiparallel configuration it has been studied to a much lesser extent than the more active parallel configuration. However, as evident from the activity at high latitudes the magnetosphere is far from static during these times and it also has a very interesting topology, making it necessary to study in more detail before a complete understanding of the system can be achieved. The study also provides an excellent platform for further, more in-depth, studies of both charged particle flows and electrodynamics related to transpolar and other high-latitude auroral arcs. The study was performed over a four-month period, and the results were published in a research journal. One important example of the expected impact of the research is that the scientists who model the magnetosphere are now provided with additional information as input to their models for the antiparallel configuration of the solar wind.
