SA032-01
Modeling Nonlinear, Time-dependent Evolution of Ionospheric Fluid Instabilities in the Polar Cap
Tuesday, 15 December 2020: 10:00
Virtual
Matthew D Zettergren, Embry-Riddle Aeronautical University, Daytona Beach, FL, United States, Leslie J. Lamarche, Geophysical Institute, University of Alaska Fairbanks, Space Physics, Fairbanks, AK, United States, Kshitija Deshpande, Virginia Tech, Blacksburg, VA, United States, Michael Hirsch, Boston University, Boston, MA, United States, Mark Redden, Embry-Riddle Aeronautical University, Daytona Beach, United States and Andres Spicher, University of Oslo, Department of Physics, Oslo, Norway
Abstract:
Small-scale plasma density irregularities are ubiquitous features of the terrestrial ionosphere at polar latitudes.
Propagation of radio waves, e.g. global positioning system (GPS) signals, is adversely affected by structures at and below the Fresnel scale, which can lead to loss-of-lock and degradation of accuracy caused by refraction and diffraction of these signals.
The main fluid-scale plasma instability thought to be responsible for polar cap density irregularities is the gradient-drift instability (GDI), which is excited in regions with a substantial plasma flow along a density gradient, conditions that exist in plasma density patches.
During nonlinear evolution of GDI, primary density structures cascade to smaller scales and form shear flow regions that are susceptible to secondary Kelvin-Helmholtz instability, while the progression of the instability can be stabilized by cross-field diffusion.
The detailed, complicated time-dependent evolution of GDI is poorly understood such that irregularities and attendant scintillation are not presently predictable, nor are we able to derive useful physical knowledge about instability progress from the scintillation.
This research focuses on high-resolution modeling of ionospheric density structures resulting from primary GDI and analysis of the progression of the GDI through nonlinear stages. For this study, we adopt the physics-based GEMINI ionospheric model, which can resolve less than 100 meter structures directly responsible for radio scintillation. Observable aspects of this instability are simulated by using plasma density output from GEMINI to drive the SIGMA radio propagation model which then provides synthetic amplitude and phase scintillation data at a range of frequencies. These results are compared against VHF, UHF, and L-band beacon data from the Resolute Bay Observatory to demonstrate basic agreement and motivate development of future, more quantitative data-driven simulation efforts.
