JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Oral

P (Space and Planetary Sciences) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM14] [EE] Dynamics in magnetosphere and ionosphere

Sat. May 20, 2017 3:30 PM - 5:00 PM 105 (International Conference Hall 1F)

convener:Tomoaki Hori(Graduate school of Science, University of Tokyo), Yoshimasa Tanaka(National Institute of Polar Research), Aoi Nakamizo(Applied Electromagnetic Research Institute, National Institute of Information and Communications Technology), Mitsunori Ozaki(Faculty of Electrical and Computer Engineering, Institute of Science and Engineering, Kanazawa University), Chairperson:Motoharu Nowada(Shandong University), Chairperson:shun Imajo(Kyushu Univ.)

4:45 PM - 5:00 PM

[PEM14-11] Space-ground coordinated observations of subauroral ion drifts (SAID)

*Toshi Nishimura1,2, Bea Gallardo-Lacourt1, Larry Lyons1, Eric Donovan3, Vassilis Angelopoulos1 (1.University of California, Los Angeles, 2.Boston University, 3.University of Calgary)

Keywords:SAPS/SAID, ring current and plasma sheet, auroral imaging and radar

Duskside plasma convection is often enhanced at narrow latitudes just equatorward of the electron auroral oval (subauroral polarization streams or SAPS). The latitudinal extent of the flows can occasionally become less than a degree with the peak speed exceeding a few km/s. Those are called subauroral ion drifts (SAID), and their formation mechanism and differences from SAPS have been key issues in subauroral magnetosphere-ionosphere coupling.

We aim at understanding occurrence timing and magnetospheric drivers of SAID by using optical imaging, radars, and low-altitude and magnetospheric satellites. Interestingly, although SAID is a subauroral phenomenon where we do not generally expect localized precipitation, all-sky imager data during a subset of SAID events showed a latitudinally narrow (~0.5 deg) auroral arc adjacent to SAID. This unique auroral feature allowed us to optically trace evolution of SAID. We found that SAID was preceded by substorm injections and SAPS, and that subsequent injections without strong proton injection resulted in SAID. This different injection behavior was confirmed by the NOAA and DMSP satellites. DMSP also showed that the bulk of the region-2 field-aligned currents (FACs) are confined to the SAID latitudinal extent. In one of the events, one of the THEMIS satellites crossed the earthward boundary of the electron plasma sheet and detected SAID with much narrower L-shell separation between electron and ion inner boundaries.

These observations indicate that SAID has a similar quasi-steady structure to SAPS both in the ionosphere and magnetosphere except for the latitudinal extent, but the type of particle injection is quite different from SAPS events; namely the injections are dominated by electrons and give much smaller separation with the ion inner boundary.