Coordinated Radar, Optical and Satellite Analysis of Plasma Sheet- Subauroral Ionospheric Coupling via Meso Scale Channels

PI: Toshi Nishimura (UCLA/BU) Co-I: Larry Lyons (UCLA) Student: Beatriz Gallardo (UCLA, now postdoc) Collaborator: Evgeny Mishin (AFRL)

AFOSR FA9550-15-1-0179 09/01/2015–08/31/2018

SAPS formaon

[Goldstein et al., 2005] SAPS: Subauroral polarizaon streams The source is the region-2 FACs driven by the ring current. The electric field is pronounced due to the low ionosphere conductance.

SAID: Subauroral ion dris SAPS with ~1 deg latude width

Importance of SAPS research

Key M-I coupling feature that involves acve ionosphere feedback

Density irregularies and radio signal scinllaon

Plasma upflow

Enhanced neutral wind

[Mishin and Blaunstein, 2008] SAPS and parcle boundary reversal

The electron precipitaon boundary is equatorward of the proton boundary when SAID occurs.

Large flow fluctuaons associated with SAID.

Proton Electron

Proton Electron

[Lyons and Williams, 1984] Purpose of this study

• What is the condition to create SAID vs. latitudinally wide SAPS? • How do SAPS connect to auroral dynamics? • What does drive the subauroral arc? • How does the subauroral ionosphere evolve during SAPS?

THM 2008-3-26 event THEMIS ASI SuperDARN NOAA DMSP DMSP SuperDARN NOAA Imagers CHAMP CHAMP THEMIS satellite Armature astronomer’s photo THEMIS all-sky imager data of the same event

0613 UT Substorm expansion phase onset 0730 UT Near the beginning of the recovery phase Arc started to emerge just equatorward of the diffuse auroral oval (~21 MLT). Extended azimuthally. Substructures propagang duskward. 0810 UT DMSP crossings 0900 UT The substorm ended. Arc disappeared Duskside subauroral arc photographed by armature astronomers

North North

Photos in courtesy of D. Anderson and C. Hall, near Anchorage, AK

The red-green mixed color is quite different from the green diffuse aurora in the oval. Is this aurora? Proton aurora? SAR arc? Or a new aurora feature? What is the mechanism to create this arc? What can we learn from this about SAPS/SAID? DMSP satellites Earlier orbit Arc conjuncon Arc conjuncon

• So precipitaon equatorward of plasma sheet electron precipitaon (à Electron aurora) • Proton precipitaon poleward of electron precipitaon (à Not proton aurora) • Subauroral ion dri adjacent to so precipitaon, narrower than usual SAPS • Weak upward and downward FACs SuperDARN radars

Before the subauroral arc formaon Wide westward flow (SAPS) Usual flow paern in the duskside subauroral ionosphere Before the arc

During the subauroral arc formaon Narrow and faster flow (SAID)

The arc is located just poleward of the flow channel. During the arc à The flow (or collisional heang) is not the cause of the arc. NOAA satellites

Trapped Precip.

Trapped protons are equatorward of electrons, but the separaon became smaller. Why can electrons penetrate as deep as protons? à Aurora and in-situ measurements DMSP and CHAMP satellites

CHAMP sunward wind What is the magnetospheric driver of the subauroral arc?

• The substorm surge and streamer near midnight à Subauroral proton aurora • The westward traveling surge propagates far from midnight. • The auroral streamers (injecons) also shi duskward à Subauroral arc • Deeper electron injecon in the premidnight sector makes the flow thinner? Surge/ Surge/ streamer streamer

Proton aurora

Surge/ streamer

Arc Arc

• The substorm surge and streamer near midnight à Subauroral proton aurora • The westward traveling surge propagates far from midnight. • The auroral streamers (injecons) also shi duskward à Subauroral arc à Injecon far from midnight makes the flow thinner? THEMIS satellites TH-C

TH-E TH-A

⊥ (-8, 4 RE) (-10, 6 RE) (-10, 15 RE)

Parcle injecon and auroral streamer locaons indeed shi duskward (22 -> 20 h MLT) as the substorm evolves in me. Coming back to the single parcle viewpoint

Proton Electron

Injecons far to the dusk will create an electron-dominated region at premidnight. Tesng the idea by Rice Convecon Model

Movie in courtesy of Jian Yang at Rice U

Le: Injecon at 24 MLT Usual ~2 RE thickness SAPS flow channel in the ring current

Right: Injecon at 21 MLT Narrower SAPS (~1 RE)

Follow the classical Region-2 FAC physics but the electron injecon closer to the Earth makes the flow channel narrower and more intense. Summary We presented a case study of SAPS/SAID and duskside subauroral thin arc using mul-instrument conjuncon (THEMIS satellites, THEMIS ASI, DMSP, SuperDARN and colored photos).

The arc is associated with low-energy (~<100 eV) electron precipitaon and thus an auroral arc. This explains the color of the arc (primarily red mixed with green) in contrast to the green diffuse aurora in the auroral oval (~1-10 keV).

The arc is adjacent to a latudinally narrow channel of flow (SAID). The arc can be used as an opcal manifestaon of SAID.

As opposed to a typical precipitaon boundary configuraon (ion precipitaon extends equatorward of electrons), electron precipitaon extends more equatorward of ions.

The arc forms aer the substorm surge reached far duskward from midnight. These suggest that electron injecon reaching deeper the premidnight inner magnetosphere than usual creates the arc and narrower SAPS. Selected papers Published • Zou, Y., Y. Nishimura, L. R. Lyons, E. F. Donovan, K. Shiokawa, J. M. Ruohoniemi, K. A. McWilliams, and N. Nishitani (2015), Polar cap precursor of nightside auroral oval intensificaons using polar cap arcs, J. Geophys. Res. Space Physics, 120, 10,698–10,711. • Nishimura, Y., and L. R. Lyons (2016), Localized reconnecon in the magnetotail driven by lobe flow channels: Global MHD simulaon, J. Geophys. Res. Space Physics, 121, 1327–1338. • Lyons, L., Y. Nishimura, Y. Zou (2016), Unsolved Problems: Meso-Scale Polar Cap Flow Channels' Structure, Propagaon, and effects on Space Weather disturbances, J. Geophys. Res., 121, 3347–3352. • Kikuchi, T., K. K. Hashimoto, I. Tomizawa, Y. Ebihara, Y. Nishimura, T. Araki, A. Shinbori, B. Veenadhari, T. Tanaka, and T. Nagatsuma (2016), Response of the incompressible ionosphere to the compression of the magnetosphere during the geomagnec sudden commencements, J. Geophys. Res. Space Physics, 121, 1536–1556. • Lyons, L. R., B. Gallardo-Lacourt, S. Zou, J. M. Weygand, Y. Nishimura, et al. (2016), The 17 March 2013 storm: Synergy of observaons related to electric field modes and their ionospheric and magnetospheric Effects, J. Geophys. Res. Space Physics, 121, 10,880–10,897. • Han, D.-S., H. Hietala, X.-C. Chen, Y. Nishimura, L. R. Lyons, J.-J. Liu, H.-Q. Hu, and H.-G. Yang (2017), Observaonal properes of dayside throat aurora and implicaons on the possible generaon mechanisms, J. Geophys. Res. Space Physics, 122, 1853–1870 (Cover figure of JGR Feb 2017 issue)

Submied • Gallardo-Lacourt B., Y. Nishimura, L. Lyons, E. Mishin, et al., Influence of auroral streamers on rapid evoluon of ionospheric SAPS flows, J. Geophys. Res.

Other acvies

Student educaon: Bea Gallardo-Lacourt

• Morris Neiburger Award, UCLA, November 2015 • Ph.D. Degree, September 2016 • Brian Bosart Award, UCLA, November 2016

Ongoing and future works:

• Publish a paper on the ongoing work • Determine the ionospheric density and scinllaon response—GPS and ISR • Find a student/postdoc • Complete the grant transfer from UCLA to BU backup Different event but with THEMIS in conjugate to the arc

DMSP-16 9:40 UT

TH-C moonlight Arc 10:25

THEMIS-C’s footprint crossed the arc.

DMSP-16 measured similar features to the 2008-3-26 event. THEMIS-C detected a localized enhancement of duskward flow = Magnetospheric counterpart of SAID

Narrow separaon between electron and ion inner boundaries (0.1 RE) as opposed to a typical separaon (~1 RE)

Broad-band waves extend above the proton gyro frequency. Lower-hybrid waves or kinec Alfven waves due to driing cold ions? fLHR Waves scaering low-energy electrons fH and creang the arc? fLHR fH