2015.08.18_ IUGONETシンポ@NIPR

SPEDASを用いたオメガバンドオーロラとPs6地磁気脈動の解析
佐藤夏雄（極地研）、門倉昭（極地研）、田中良昌（極地研）、堀智昭（STE研）、行松彰（極地研）

発表概要
1. Introduction* Pulsating aurora* Omega band aurora
2. Observation
2‐1. Omega band pulsating aurora observed at SNKQ on 1 March 2011
+ Simultaneous observation onboard THEMIS and on the ground‐ Optical signature‐ THEMIS Observation
2‐2. Event survey using THEMIS ASI network‐ How to find Omega event from THEMIS summary plots‐ Total number and MLT dependence
2‐3. Case study of Optical signatures and their relation to Ps6 magnetic pulsation
2‐4. Initial results of SuperDARN observation
3. Summary and Discussion

Pulsating Auroras (PsA): Brief review• PsA are observed universally during the recovery phase of substorms in
the auroral and sub-auroral zones.
•Activities are more prominent in the postmidnight to morning side.
• Main period is ranges from a few seconds to a few tens of second.
• Higher frequency internal modulations of ~3 Hz or faster are often•Shapes are irregular patches, E-W bands, omega-band structure.
• Energies of modulated electron fluxes are a few keV to 100 keV

Mechanism isstill Opendiscussion

Example of Pulsating Auroras observed at Syowa TV

All‐sky TV camera〜6 sec main
periodmodulation〜3Hz higher
frequency
internalmodulation

Pulsating Auroras (PsA): Open Questions

Questions
Fundamental characteristics☆ON‐OFF modulation（tens of second and a few Hz）☆ Formation of shapes（Patch, E‐W band, Omega band）☆ Movement（Standing, Poleward movement）
Generation Mechanism?
☆Pitch‐angle scattering via wave‐particle interaction (Standard model)☆DC electric field modulation? (Sato et al., 2004)

Type/Classification of PsA

Generation
mechanism may bedifferent at
different type of
pulsating aurora!

PatchE‐W band

Omega band
orTorch‐like structureOmega bands/Torch‐like structure

Omega bands

Torchesfrom DMSP spacecraftBrief review of Omega bands/Torches
Observation signature‐ Shapes are which resembles an inverted Greek letter Ω.
‐ Scale sizes are 400‐1000 km‐ Occurrence local time is midnight to early morning‐ Substorm recovery phase‐ Eastward drift with speed of 0.2‐4 km/sec‐ Psc6 magnetic pulsation with period of 5‐40 min‐ Fine structure consists with Pulsating aurora

Generation mechanism (?)
There is no commonly accepted understandings of the formation
mechanism of omega band aurora
1. KH instability (Rostoker and Samson:1984)
2. Rayleigh‐Taylor (Interchange) instability (Yamamoto:1997)
3. M‐I coupling instability (Lyatsky and Maltsev: 1984)
4. Field‐aligned electric field ( Jorgensen etal. :1999)

Omega band aurora and Ps6 magnetic pulsation
Solovyev et al., 1999.JGR
最初の発見者はSaito [1978]。
Pi 3タイプで蛇行したオーロラの形状を予測した

Brief review of Omega bands/Torches
Observation signature‐ Shapes are which resembles an inverted Greek letter Ω.
‐ Scale sizes are 400‐1000 km‐ Occurrence local time is midnight to early morning‐ Substorm recovery phase‐ Eastward drift with speed of 0.2‐4 km/sec‐Retaining their shapes for several minutes‐Psc6 magnetic pulsation with period of 5‐40 min‐ Fine structure consists with Pulsating aurora

Generation mechanism (?)
There is no commonly accepted understandings of the formation
mechanism of omega band aurora
1. KH instability (Rostoker and Samson:1984)
2. Rayleigh‐Taylor (Interchange) instability (Yamamoto:1997)
3. M‐I coupling instability (Lyatsky and Maltsev: 1984)
4. Field‐aligned electric field ( Jorgensen etal. :1999)

2011.03.01
Omega band Pulsating Aurora
observed at Sanikiluaq (SNKQ) in Canadaand THEMIS‐D and E spacecraft

Sato et al., 2015. JGR2015_JGR special issue on "Pulsating Aurora and Related
Magnetospheric Phenomena""Omega band pulsating auroras observed onboard
THEMIS spacecraft and on the ground"by Natsuo Sato, Akira Kadokura, YoshimasaTanaka, Takanori Nishiyama, Tomoaki Hori, Sessai AYukimatu

Movie: Life cycle of Omega band auroraSignatures of Omega band aurora on the groundAll‐sky image

Omega band aurora

Keogram

Ps6 magnetic pulsations
T= ~ 10‐20 min

Pi1C magnetic pulsations

Signatures of Omega band aurora on the groundAll‐sky image

Omega band aurora

Keogramband‐pass filter
Ps6 magnetic pulsations
T= ~ 10‐20 min

high‐pass filter
Pi1C magnetic pulsations

Sato et al., 2015. JGRLife cycle of Omega band auroraGrowth of Omega band PsA
The omega band aurora grew from a faint seed, not via
distortion of a pre‐existing east‐west band aurora

The aurora did not show any shear motion during thegrowth of auroral activity

A black hole‐like dark region was found during thegrowth and expansion phases at the east side of the omega
band aurora

Sato et al., 2015. JGROmega band Pulsating Auroras

PsA
PsA
PsA
PsA
Sato et al., 2015. JGR

PsA
PsA

Omega band Pulsating Auroras

Poleward moving form

Pulsation period is ~ 9‐12 sec

Sato et al., 2015. JGRExpansion/Maximum period of Omega band aurora

every 3 second data
* Poleward moving form

* Complex segments

Sato et al., 2015. JGRMovie: Expansion/Maximum period of Omega bandPulsating Aurora

Expansion/Maximum period of Omega band Pulsating
AuroraSato et al., 2015. JGR

THEMIS satellite observation of Omega band aurora

footprintorbit

T96 model using following parameters: Dst, solar windpressure, IMF, By, and Bz were +20.0 nT, 7.0 nPa, 2.0 nT, and7.5 nT.
Sato et al., 2015. JGR

THEMIS‐D and E satellite observation

Electric field* DC electric field showed significant quasi‐periodic intensity variations
together with the optical omega band pulsating aurora and with a period of
about 15‐20 s
Inside ofOmega bandaurora*Z component had the highest variability of ~2.7 mV/m peak to peak;that of the Y component was ~1.8 nV/m peak to peak

ELF wave*Electrostatic low‐frequency waves of less than 30 Hz showed
quasi‐periodic intensity variations similar to the DC electric field variation

Sato et al., 2015. JGRAnother example of Omega band PsA: 2009‐02‐27 event

All‐sky image2009.02.27
event

FSMI

Electric field*DC electric field show impulsive intensity variations*Z component is the largest

Sato et al., 2015. JGR

THEMIS‐E

2‐2. Event survey from THEMIS ASInetwork＊Total number＊MLT dependence
How to find Omega event fromTHEMIS summary plots?

THEMIS: Coordinated space and ground observation

THEMIS: Coordinated All‐sky imager network
2011.03.01.0736:06UTTHEMIS: Coordinated All‐sky imager network

ASI Summary plots

THEMIS: Coordinated All‐sky imager network

Keogram Summary plots

Where is Omega
band aurora?

THEMIS: Coordinated All‐sky imager network

THEMIS: Coordinated All‐sky imager network
20110301_13‐14_gako‐keogram.pgm

THEMIS: Coordinated All‐sky imager network
20110301_13‐14_gako‐montage.pgm

Magnetic local time (MLT) dependence of Omega aurora
2008〜2014

Total Event Number：~ 1502013.09.02 event

2013.09.02
Omega band Pulsating Aurora
observed at Sanikiluaq (SNKQ) in Canada

2013.09.02_ SNKQ event

2013.09.02 Omega band aurora at SNKQ

2013.09.02 Omega band aurora at SNKQ

2013.09.02 Omega band aurora at SNKQ

2013.09.02 Omega band aurora at SNKQ

2013.09.02 Omega band aurora at SNKQ

2013.09.02 Omega band aurora at SNKQ

2013.09.02 Omega band aurora at SNKQ

Omega band aurora and Ps6 magnetic pulsation at SNKQ

Ps6
magnetic pulsation

2014.02.23 event at FSIM

2014.02.23
Omega band Pulsating Aurora
observed at Fort Simpson (FSIM) inCanadaOmega band aurora and Ps6 magnetic pulsation

Ps6
magnetic pulsation
Pi3 Saito 1973

Omega band aurora and Ps6 magnetic pulsation

Intensity‐ X comp => ??
Intensity‐ Y comp => In phase
Intensity‐ Z comp => 90° delay

Y‐com/max= Z‐comp /zero2011.03.01

Omega band event
observed at Mcgrath and Gakonain Alaska

Omega band event on March 1, 2011

Very active Omega band event• March 1, 2011 event

MCGR (Mcgrath, AK)
GAKO (Gakona, AK)Omega band aurorsa at MCRG and GAKO

Omega band

Keogram

2011.03.01~ 0200 MLT~ 0430‐0500 MLT~ 0230‐430 MLT~ 0230‐0400 MLT~ 0130‐0300 MLT

Omega band event on March 1, 2011

Movie of Omega band observed at MCGR/GAKOGrowth of Omega band Pulsating Aurora

Growth signature of Omega bandauroraGrowth of Omega band Pulsating Aurora

1304

1306

1312

1314

1320

1322

1308

1316

1324

1310

1318

1326

Omega bands observed at GAKO

Growth of Omega band Pulsating AuroraOmega bands observed at GAKO

Growth of Omega band Pulsating AuroraGrowth of Omega band Pulsating Aurora

Relation between Omega bandauroras and Ps6 Magneticpulsations

Omega band aurora and Ps6 magnetic pulsation
Keogram(GAKO)

Ps6 (X‐comp)Ps6 (Y‐comp)T~ 10‐20 min
Ps6 (Z‐comp)Omega band aurora and Ps6 magnetic pulsationKeogram(GAKO)

Good correlation between Peak of
Keogram and Ps6 (Y‐comp)Ps6 (X‐comp)Ps6 (Y‐comp)Ps6 (Z‐comp)

Omega band aurora and Ps6 magnetic pulsation
Keogram(GAKO)
Aurora intensity
at Zenith
Ps6 (Y‐comp)Excellent correlation between aurora
Ps6 (Z‐comp)intensity and Ps6 (Y‐comp)Ps6 (X‐comp)Omega band aurora and Ps6 magnetic pulsation
Equivalent current

Aurora Intensity
at ZenithmaxmaxY‐compmin~zeromin~zero~zeroZ‐compOmega band aurora and Ps6 magnetic pulsation

Equivalent currentPoleward current
Poleward current

Equatorward current

Equatorward current

Omega band aurora and field‐aligned current
Opgenooth et al., 1983.JGR

2011.03.01

Omega band event
observed at Mcgrath and Gakona inAlaska
compared with
SuperDARN radars at
Kodiak and King Salmon

THEMIS all‐sky camera network and SuperDARNSD observation of Omega band aurora
FOV of

FOV ofMcgrath (MCRR), Alaska

Gakona (GAKO), Alaska

Initial results ofSuperDARN observation ofOmega band aurora

KingSalmon
KodiakSD observation and Omega band aurora
FOV of

FOV ofMcgrath (MCRR), Alaska

Gakona (GAKO), Alaska

KingSalmonKodiak

Event (1)Omega band aurora and Convection by SD

1345UT1347UT

1349UT1351UT

Omega band aurora and Convection by SD

Electric field enhanced when Omega band aurora enhanced

2011.10.30

Omega band event
observed at Kiana in Alaska
compared with
SuperDARN radars at
Kodiak and King Salmon

Omega band aurora and Convection by SD

Omega band aurora and Convection by SD

Omega band aurora and Convection by SD

2008.03.09 Saskatoon SD/Gill ASI
0935 UTOmega band aurora and Convection by SD

0932 UT

0935 UTSummary and Conclusion (1)(1): Optical signature on the groundA torch‐like structure omega band pulsating aurora wasobserved simultaneously on the ground and onboard theTHEMIS spacecraft.
*The omega band aurora grew from a faint seed, not via
distortion of a pre‐existing east‐west band aurora.
*The aurora did not show any shear motion during the growthof auroral activity.
*The aurora drifted eastward with a speed of ~0.25 km/s.
*A black hole‐like dark region was found during the growthand expansion phases at the east side of the omega bandaurora.
*The meso‐scale omega band aurora consisted of more than
15 patches of complex‐shaped small‐scale auroras.
*Each patch showed an intense pulsating aurora with arecurrent period of ~9‐12 s and a poleward‐moving form.

Summary and Conclusion (2)(2) Omega band aurora and Ps6 magnetic pulsation*Ps6 (Y) and aurora intensity showed one to one correlation*Ps6 (Y) became maximum when omega aurora arrived at thezenith*Ps6 (Y) became minimum when black hole‐like dark region arriveat zenith*Ps6 (Z) became zero when both of Ps6 (Y) became maximum
and minimum(3) Equivalent Current of Ps6 magnetic field*Equator current is associated with omega band aurora*Poleward current is associated with the back hole‐like dark
region*That is, Ps6 magnetic pulsations occurred in association with thetemporal and spatial variation of Omega band aurora(4) Initial result of SuperDARN radar*Electric field intensity enhanced when Omega band aurora
enhanced*We need further work!

Future work(1): Generation signature of Omega band aurora• Statistical signatures with relation to IMF• Initial optical signature of growth of aurora• SuperDARN• NIPR Data (Syowa: unmanned magnetometer）, Iceland,Tromso (EISCAT)• Survey of simultaneous events of Satellite and on the ground(2): Catalogues (Photo and Movie• Pulsating aurora• Omega band aurora

Acknowledgements＊THEMIS Science Support team＊IUGONET 開発team＊ERG‐Science Center team