Conference Agenda

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Session Overview
2AM1: Aurora
Tuesday, 21/Mar/2017:
8:30am - 10:05am

Session Chair: Eric Frank Donovan
Session Chair: Pierre Langlois

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8:30am - 8:45am

Alfvénic Dynamics and Structuring of Discrete Auroral Arcs: Swarm and e-POP Observations

David Miles1, Ian Mann1, Ivan Pakhotin1, David Knudsen2, Johnathan Burchill2, Andrew Howarth2, Don Wallis2

1University of Alberta, Canada; 2University of Calgary, Canada

Dynamic dual discrete arc aurora with anti-parallel flow along the arcs was observed nearly simultaneously on March 11, 2016 by the enhanced Polar Outflow Probe (e-POP) and the adjacent Swarm A and C spacecraft. Auroral imaging from e-POP reveal 1-10 km structuring of the arcs which move and evolve on second timescales and confound the traditional field-aligned current algorithms. High-cadence magnetic data from e-POP shows 1-10 Hz, presumed Alfvénic, perturbations co-incident with, and at the same scale size as, the observed dynamic auroral structures. Analysis of high-cadence E- and B- field data from the adjacent Swarm A spacecraft reveals non-stationary electrodynamics involving reflected and interfering Alfvén waves and signatures of modulation consistent with trapping in the Ionospheric Alfvén Resonator (IAR). Taken together, these observations suggest a causative role for Alfven waves, perhaps also the IAR, in discrete arc dynamics on 0.2 - 10s timescales and ~1-10 km spatial scales.

8:45am - 9:00am

Optical Signatures of Field Line Resonances: Comprehensive Survey and Precipitation Mechanisms

D. Megan Gillies, Eric Donovan, David Knudsen, Emma Spanswick, Frances Fenrich

University of Calgary, Canada

Auroral arcs are perhaps the best known example of a cosmic plasma process, and have been the focus of scientific interest for well over a century. Advances in optical instrumentation have enabled the identification of over 300 auroral arcs with an infrequently observed auroral morphology. We observe this morphology with the 6300 Å auroral emission wavelength and have connected it to global magnetospheric wave modes known as field line resonances (FLRs). Here we present FLR observations from the redline geospace observatory (REGO) and the recently launched European Space Agency Swarm mission. We will demonstrate that this particular class of auroral arc is associated with FLRs.

9:00am - 9:15am

Swarm Observation of Field-Aligned Currents In Multiple Arc System

Jiashu Wu, David Knudsen, Eric Donovan, Deborah Gillies, Johnathan Burchill

University of Calgary, Canada

It is often thought that auroral arcs are a direct consequence of upward field-aligned currents. In fact, the relation between currents and brightness is more complicated. Multiple auroral arc systems provide and opportunity to study this relation in detail. In this study, we have identified two types of FAC configurations in multiple parallel arc systems using ground-based optical data from the THEMIS all-sky imagers (ASIs), magnetometers and electric field instruments onboard the Swarm satellites during the period from December 2013 to March 2015. In type 1 events, each arc is an intensification within a broad, unipolar current sheet and downward currents only exist outside the upward current sheet. In type 2 events, multiple arc systems represent a collection of multiple up/down current pairs. By collecting 17 events for type 1 and 12 events for type 2, we find that (1) Type 1 events are mainly located between 22-23MLT. Type 2 events are mainly located around midnight. (2) Upward currents with more arcs embedded have larger intensities and widths. (3) Type 1 events preferentially occur either before substorm onsets or without a substorm accompanying, while there are more events in Type 2 category happening within one hour after substorm onset. (4) The arcs in the Type 2 multiple arc system are wider and more separated. This information will be used as a test of models of quasi-static arc formation.

9:15am - 9:30am

Ionospheric Electron Heating Associated With Pulsating Auroras --- Swarm Survey and Model Simulation

Jun Liang, Bing Yang, Eric Donovan, Johnathan Burchill, David Knudsen

University of Calgary, Canada

In this study, we report a survey on the ionospheric plasma signatures (electron temperature, plasma density and field-aligned current etc.) of pulsating auroras using Swarm satellite data. Via the survey of 37 patch crossing events, we repeatedly identify a strong electron temperature enhancement associated with the pulsating aurora. On average, the electron temperature at Swarm satellite altitude (~460 km) increases from ~2100 K at sub-auroral altitudes to a peak of ~3000 K upon entering the pulsating aurora patch. This indicates that the pulsating auroras act as an important heating source of the nightside ionosphere/thermosphere. On the other hand, no well-defined trend of plasma density variation associated with pulsating auroras is identified in the survey. The field-aligned currents within the pulsating aurora patch are mostly upward, with mean magnitude on order of ~ 1 uA/m2. We then perform a numerical simulation to explore the potential mechanisms that may account for the strong electron heating associated with the pulsating aurora. Via the simulation we find that, to account for the realistic electron temperature observation, the pulsating auroras would likely be associated with a substantial magnetospheric heat flux on order of ~1010 eV/cm2/s. We propose that such a magnetospheric heat flux may be pertinent to one long-hypothesized nature of pulsating auroras, namely the coexistence of a magnetospheric cold-plasma population in addition to energetic electrons constituting the pulsating auroral precipitation.

9:30am - 9:45am

Aurorasaurus Citizen Science Observations of Aurora During the Solar Maximum

Elizabeth A. MacDonald

NASA Goddard Space Flight Center, United States of America

The Aurorasaurus citizen science project has been collaborating with a global network of amateur observers for four years resulting in a validated new database for auroral studies. These studies have shown the scientific value of crowd-sourced observations for ground-truthing of coarse, statistical auroral models as well as disruptive, discovery based science. We will discuss the background and operations of the Aurorasaurus platform with public participation in research. One unexpected result is that significant numbers of people are able to see aurora during storms further south than the leading model would predict. A second unexpected result is the discovery of the STEVE phenomena by citizen scientists. We will highlight new results showing the improvements possible to aurora modeling and knowledge by combining non-traditional soft sensor techniques with traditional ground-based imaging and satellite conjunctions, such as SWARM and the University of Calgary all-sky camera arrays.

9:45am - 10:00am

Mesoscale Magnetosphere-Ionosphere Coupling Along Open Magnetic Field Lines Associated with Airglow Patches: Field-Aligned Currents and Precipitation

Ying Zou1, Yukitoshi Nishimura1,2, Larry Lyons1, Kazuo Shiokawa3, Johnathan K. Burchill4, David J. Knudsen4, Stephan Buchert5, Steve Chen6, Michael J. Nicolls6, J. Michael Ruohoniemi7, Kathryn A. McWilliams8, Nozomu Nishitani9

1Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, USA; 2Department of Electrical and Computer Engineering and Center for Space Physics, Boston University, Boston, Massachusetts USA; 3Center for International Collaborative Research, Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan; 4Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada; 5Swedish Institute of Space Physics, Uppsala, Sweden; 6SRI International, Menlo Park, California, USA; 7The Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, Virginia, USA; 8Institute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.; 9Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan

Although airglow patches are traditionally regarded as high-density plasma unrelated to local field-aligned currents (FACs) and precipitation, past observations were limited to storm-time conditions. Recent non-storm time observations show patches to be associated with azimuthally narrow ionospheric fast flow channels that substantially contribute to plasma transportation across the polar cap and connect dayside and nightside explosive disturbances. We examine whether non-storm time patches are related also to localized polar cap FACs and precipitation using Swarm- and FAST-imager-radar conjunctions. In Swarm data, we commonly (66%) identify substantial magnetic perturbations indicating FAC enhancements around patches. These FACs have substantial densities (0.1-0.2 μA/m-2) and can be approximated as infinite current sheets (typically 75 km wide) orientated roughly parallel to patches. They usually exhibit a Region-1 sense, i.e. a downward FAC lying eastward of an upward FAC, and can close through Pedersen currents in the ionosphere, implying that the locally enhanced dawn-dusk electric field across the patch is imposed by processes in the magnetosphere. In FAST data, we identify localized precipitation that is enhanced within patches in comparison to weak polar rain outside patches. The precipitation consists of structured or diffuse soft electron fluxes. While the latter resembles polar rain only with higher fluxes, the former consists of discrete fluxes enhanced by 1-2 orders of magnitude from several to several hundred eV. Although the precipitation is not a major contributor to patch ionization, it implies newly reconnected flux tube that retain electrons of magnetosheath origin can rapidly traverse the polar cap from the dayside. Therefore non-storm time patches should be regarded as part of a localized magnetosphere-ionosphere coupling system along open magnetic field lines, and their transpolar evolution as a reflection of reconnected flux tubes traveling from the dayside to nightside magnetosphere.

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