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 1:45 PM - 3:15 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.)

2:20 PM - 2:35 PM

[PEM14-03] SECS reconstruction of flow fluctuations with SuperDARN data

*Tomoaki Hori1, Nozomu Nishitani2, Kunihiro Keika1, J. M. Ruohoniemi3, Mariko Teramoto2, Akimasa Ieda2, Shin'ya Nakano4, Kanako Seki1, S. G. Shepherd5, W. A. Bristow6 (1.Graduate school of Science, University of Tokyo, 2.ISEE, Nagoya Univ., 3.Virginia Tech, 4.Institute of Statistical Mathematics , 5.Dartmouth College, 6.Univ. of Alaska, Fairbanks)

Keywords:ionosphere, ULF, SuperDARN

We further analyze detailed properties of two-dimensional (2-D) structures of the ULF-like, ionospheric flow fluctuations during a short (~2 hours) break of the main phase of the March 2015 storm. Line-of-sight (LOS) Doppler velocities observed by two SuperDARN radars in the early morning sector were used to deduce the 2-D horizontal flows by means of the spherical elementary current system (SECS) expansion. Similar to results deduced by the conventional map potential technique, the SECS reconstruction shows that ionospheric plasma in the subauroral region flows primarily in the geomagnetically eastward direction before and after the period of the ULF-like fluctuations. The reconstructed flow pattern shows that, during the first half of the ULF event interval, background convection subsides and circular/elliptically polarized flow fluctuations pass over the field-of-view of the radars as they propagate westward. Multiple flow bursts likely associated with small injections occur concurrently during the second half period, while the westward-propagating flow fluctuations still continue regardless of the bursts until a major substorm activity starts later on. Some eastward-propagating flow fluctuations are seen in the early morning sector upon onset of the major substorm, which is strongly suggested by the fact that multiple injections are seen around midnight by Van Allen Probes and the SYM-H and AL indices resume growing. A new finding from the reconstructed flow then is that the eastward-propagating structures are also dominated by a poloidal component. The common feature of poloidal-dominant fluctuations implies that the westward- and subsequent eastward-propagating fluctuations are both caused by a similar mechanism.