Joint Astrophysics/Space Physics Seminar
"In Situ Studies of Irregularities in the Cusp Ionosphere" by Andres Spicher, Ph.D., Department of Physics, University of Oslo
Abstract: Plasma irregularities spanning a wide range of scales are common in the F region ionosphere, especially in the cusp. Understanding and characterizing the physical phenomena responsible for them is not only important from a theoretical point of view, but also in the context of space weather, as the plasma perturbations can disturb HF communication and Global Navigation Satellite Systems signals. Overall, research about the small-sized irregularities has not progressed as fast at high latitudes as at low latitudes, and there is still no detailed explanation regarding their formation. In the classical view, density gradients associated with polar cap patches, flow shears and particle precipitation are regarded as dominant sources of free energy for their creation. To investigate the role of different structuring mechanisms, we use Swarm data and high resolution measurements from the Investigation of Cusp Irregularities (ICI) sounding rockets. From those measurements and by using higher-order spectra and statistics, we give further evidences of the importance of the gradient drift instability and of particle precipitation. Additionally, observations from ICI3 reveal that reverse flow events, i.e., flow channels with velocity opposite to that of the large-scale background flow, are highly structured, with the presence of meter-scale irregularities, several internal flow shears and intense particle precipitation. Those results provide new insights into the nature of the plasma structuring in the cusp ionosphere at F region altitudes."