Observations of Auroral Ionopheric Response Effects As Seen By the MICA Sounding Rocket

Friday, 19 December 2014: 9:00 AM
Kristina A Lynch1, Peter Horak1, Philip A Fernandes1, Matthew D Zettergren2, Donald L Hampton3, Mark Conde3, David L Hysell4, Robert J Miceli4, Steven Powell4, Marc Lessard5, Joran Idar Moen6, Robert Michell7, Marilia Samara7 and Michael J Nicolls8, (1)Dartmouth College, Hanover, NH, United States, (2)Embry-Riddle Aeronautical Univ, Daytona Beach, FL, United States, (3)University of Alaska Fairbanks, Fairbanks, AK, United States, (4)Cornell University, Ithaca, NY, United States, (5)University of New Hampshire Main Campus, Durham, NH, United States, (6)University of Oslo, Oslo, Norway, (7)Southwest Research Institute, San Antonio, TX, United States, (8)SRI International, Menlo Park, CA, United States
The auroral sounding rocket mission MICA provides an observational case study of nightside auroral ionospheric conductivity and field structuring, and the relationship of this structure to small-scale downward (return) currents. A large-scale current sheet is observed within an auroral arc, with a scale size comparable to that of the arc. Fine-scale return current structures are seen poleward of the visible arc, with scale sizes comparable to the structuring seen at the boundary of the visible arc. Interpretation of the field signatures as indicators of curl B and div E requires careful consideration of the arc geometry and the obliqueness of the measurement trajectory. Ground imaging data and collocated PFISR observations provide context for the in situ observations. The in situ observations starkly illustrate the inability of the radar to capture the small-scale structuring involved in the ionospheric feedback as indicated by the in situ observations. Upgoing Poynting flux and downward currents in the return current region have scale sizes of kilometers or less in the perpendicular-to-B direction, compared to a PFISR resolution of tens of km (limited by beam spacing for our experiment.) We present comparisons of the observed field-aligned current strengths to terms of the current continuity equation involving gradients of the Pedersen conductivity and the divergence of E, and discuss ionospheric sourcing of return currents. We compare the observations to the calculations of an ionospheric electrostatic model, and discuss the requirements for capturing the ionospheric responses to auroral drivers.