Physics and Astronomy Space Plasma Seminar - Matt Zettergren - ERAU

Title: "Plasma Density Cavities in the Auroral Ionosphere: Formation, Evolution, and Instability"

January 24, 2017
3:30 pm - 4:30 pm
Location
Wilder 202
Sponsored by
Physics & Astronomy Department, Thayer School of Engineering
Audience
Public
More information
Tressena Manning
603-646-2854
Abstract: The terrestrial auroral ionosphere is home to a rich variety of plasma phenomena associated  with energy input via energetic particles and electric fields imposed by coupling with the overlying magnetosphere.  One particular example is ionospheric F-region plasma density cavities - depletions with densities of 20-75% of background - which are often observed in close proximity to auroral arcs.  Density cavities are typically elongated along the arc-tangent direction and ~10-50 km wide in the arc-normal direction.  These mesoscale features can impact various aspects of magnetosphere-ionosphere coupling as they represent a variable plasma source to the magnetosphere and also generate conditions favorable for instabilities that lead to small-scale irregularities.  Prior work indicates that the structure of electrical currents in auroral arcs serves as a depletive mechanism in the downward current channel.  However, there are other ionospheric loss processes, most prominently energy-dependent recombination and field-aligned transport, that have not been fully explored as causative agents for auroral density cavities.  Furthermore, available observations are not able to directly distinguish between the various cavity generation mechanisms; hence, we do not yet have a complete understanding of these processes and their implications for the ionosphere-magnetosphere system.  

This talk outlines the recent development of a new set of numerical models specifically aimed at understanding the physical mechanisms leading to the formation of plasma density cavities and the evolution and stability of these cavities.  Our model is used to illustrate the relative balance of depletive mechanisms contributing to the formation of the density cavities.  Results are validated against phased-array incoherent scatter radar measurements of density cavities from the PFISR and RISR systems through carefully constructed, data-driven case studies.  Finally, the model is used to illustrate the degree to which density structures (including cavities) are susceptible to gradient-drift instability, which may lead to small-scale density structures capable of causing GPS scintillation.  
Location
Wilder 202
Sponsored by
Physics & Astronomy Department, Thayer School of Engineering
Audience
Public
More information
Tressena Manning
603-646-2854