Reporter Review: Auroral Phenomena

Clare E. J. Watt University of Alberta

26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Auroral Processes in the Magnetosphere

• Aurora are caused when particles impact the upper atmosphere with sufficient energy to excite neutral atoms • In order to precipitate, particles (electrons or protons) must have small enough pitch-angles to prevent trapping in the magnetic bottle created by the Earth’s magnetosphere.

• This review will focus on recent advances in the study of magnetospheric processes which cause auroral particle precipitation.

After Figure 3.1, Baumjohann and Treumann, [1997] 26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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www.phys.ualberta.ca/~cwatt/reporter_review

• Papers selected were published between July 2007 and June 2009.

• 214 articles from peer-reviewed sources: Journal of Geophysical Research

(JGR)

Annales Geophysicae

(AG)

Geophysical Research Letters

(GRL)

Physics of Plasmas

(PoP)

Physical Review Letters

(PRL)

Science Advances in Space Research

(ASR)

Journal of Atmospheric and Solar Terrestrial Physics

(JASTP)

Earth, Planets & Space

(EP&S)

Nonlinear Processes in Geophysics

(NPG)

Planetary and Space Science

(P&SS)

Journal of Plasma Physics

(JPP)

Physica Scripta

(Phys. Scr.)

Reviews of Geophysics

(RG)

Space Science Reviews

(SSR)

Plasma Physics & Controlled Fusion

(PPCF) 26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Structure of Review

• Magnetospheric physics of auroral precipitation: – Quasi-static acceleration processes (upward & downward current) – Dynamic acceleration processes (e.g. Alfvén waves) • Consequences of auroral precipitation – Auroral Kilometric Radiation – Ion outflow from the ionosphere • Auroral phenomenology – Substorms – Solar-wind driven aurora – Aurora equatorward of auroral oval

Figure 4.1 Paschmann et al., [SSR 2002] Reporter Review: Div III Auroral Processes C. E. J. Watt 26 th August 2009

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Quasi-static acceleration processes

• Field-aligned acceleration – Field-aligned parallel electric field – Concentrated parallel electric fields; Transition layers; Double layers – Inverted-V electrons in situ

Figure 1 [Partamies et al., AG, 2008] Shows typical inverted-V signature from in-situ FAST data Figure 2(b) [Ergun et al., GRL 2000] Concentrated potential drops/E || 26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Parallel electric fields: Double layers

Earthward energy flux Anti-earthward flux electric potential Integrated study of Double Layers in downward current region: • FAST observations

[Andersson et al., PoP 2008]

• Vlasov simulations

Newman et al., PoP, 2008a, 2008b] Figure 2, Andersson et al., PoP, 2008 Reporter Review: Div III Auroral Processes 26 th August 2009 C. E. J. Watt

0.26 s

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• •

Control of Double Layers

Singh et al.,

[JGR 2009]

show through self-consistent 2D PIC simulations how a potential drop manifests as a series of moving DLs and density cavities Hwang et al.,

[JGR 2009a, 2009b]

FAST electron observations to deduce how the potential drop varies with magnetospheric and ionospheric use parameters (tests previous analytical results: Cran-McGreehin and Wright

, JGR 2005

)

Figure 2(b) [Ergun et al., GRL 2000] Concentrated potential drops/E || 26 th August 2009 Figure 8, Hwang et al., JGR 2009a Reporter Review: Div III Auroral Processes C. E. J. Watt

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Source & Structure of Upward Current

• Haerendel

, [JGR 2007, 2008, 2009

] shows that in a static model, upward j || can be driven by magnetic stress release in the near-Earth plasma sheet due to radial pressure gradients – Makes predictions which could be tested with sounding rockets or low altitude spacecraft.

Figure 3, Haerendel, JGR 2007

• Theory of stationary inertial Alfvén waves

[orig. Knudsen JGR 1996; expanded by Finnegan et al., NPG 2008; PoP 2008; PPCF 2008]

tested in the laboratory

[Koepke et al., PPCF 2008]

– can structure a large-scale current sheet into smaller perpendicular structures, without requiring a structured source

26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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•

Inverted-V electrons

Partamies et al., [AG 2008]

show occurrence and characteristics of inverted-V electron signatures using 5 years of quicklook FAST data

Occurrence vs MLT Scale size PC potential vs energy

Figure 6 Figure 9

Red curve = occurrence of auroral arcs in MLT

[Syrj äsuo and Donovan, AG 2004].

26 th August 2009

Peak at 20-40km

Reporter Review: Div III Auroral Processes C. E. J. Watt Figure 8

Black line = 3 x Energy 9

Dynamic acceleration processes

• Shear Alfvén waves with small perpendicular extent can support time-varying and propagating E || • Dynamic auroral displays – Generation of waves in magnetosphere – Cause of short perpendicular scales – Wave-particle interactions

26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Generation of shear Alfvén waves which drive aurora

Magnetotail driving

• A mechanism for wave conversion from magnetosonic to shear Alfvén waves on very stretched or open field lines

[Pilipenko et al., JGR 2008]

• Wright and Allan

[JGR 2008]

use a simplified fluid model of the magnetotail to show how a plasmoid can drive Alfvénic disturbances with observed characteristics in both lobe and plasma sheet

“Local” driving

• Observational evidence for shear Alfvén waves driven by the shear flow in an inverted-V structure in Reimei data

[Asamura et al., GRL 2009] 26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Short perpendicular scales

•

What causes short perpendicular scales in shear Alfvén waves?

• Chaston et al., cascade

[PRL 2008]

show using FAST observations that Alfvénic aurora may be powered by a turbulent • Conversion of large-scale shear Alfvén waves to small scale inertial Alfvén waves seen in 2.5D PIC simulation

[Khazanov and Singh, PPCF 2008]

requires small-scale density cavities

• Ionospheric control of perpendicular scales

[Streltsov, JGR 2007; Lysak and Song, GRL 2008; Sydorenko et al., JGR 2008] Figure 2, Chaston et al., PRL 2008 Reporter Review: Div III Auroral Processes C. E. J. Watt

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26 th August 2009

Characteristics of auroral SAW - modelling

Inhomogeneous plasma

• A dispersion relation for kinetic Alfvén waves in plasma with perpendicular plasma gradients

[Lysak, PoP 2008]

– cavities, boundaries between lobe/plasma sheet • Alfvénic solitons in inhomogeneous plasma supporting E ||

[Stasiewicz,PPCF 2007; Stasiewicz & Ekeburg, NPG 2008]

Ionospheric feedback

• Inclusion of ionospheric feedback important for SAW evolution – Conductivity evolution

[Lu et al., JGR 2007, 2008]

– Ionospheric heating

[Streltsov., JGR 2008]

• Ionospheric feedback instability characteristics different from FLR

[Lu et al., JGR 2008]

• Ionospheric feedback instability model provides new interpretation for localized e-m waves observed by Cluster at ~5R

[Streltsov & Karlsson, GRL 2008]

E in the PSBL

26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Electron acceleration by shear Alfvén waves

(top) Figure 2, Watt et al., PRL 2009 (bottom left) Figure 6(a) Wygant et al., JGR 2002

• Self-consistent model of electron acceleration by SAW in warm plasma: – Propagating SAW

al., PRL 2009

– Standing SAW

al., GRL 2007 - Watt et - Rankin et

• c.f. Polar observations of SAW and electron acceleration at ~5R E in the PSBL

[Wygant et al., JGR 2002]

• Self-consistent simulations also show that acceleration by SAW can cause trapped magnetospheric populations and precipitation in the opposite ionosphere

[Swift, JGR 2007] (bottom right) Figure 3(b) Watt et al., PRL 2009 26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Flickering/Pulsating Aurora

• New instrumentation ideal for studying auroral processes with short temporal scales: – e.g. Reimei satellite, ASK, all-sky TV cameras, EMCCD detector • Stability and coherence of electron precipitation over different time scales using DMSP data

[Boudouridis and Spence, JGR 2007]

• Flickering aurora –spatial scales 50m 1km and frequencies 1-20Hz – Observations consistent with model of interfering electromagnetic waves

[Whiter et al., GRL 2008; Gustavsson et al., JGR 2008]

– Observations consistent with dispersive characteristics of Alfvén waves at ~6Hz

[Semeter et al., JGR 2008] Figure 9, Semeter et al., JGR 2008 26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Reimei satellite (ISAS)

Name Objectives Launch Date Location Launch Vehicle Configuration Orbit Altitude: Inclination REIMEI Demonstration of next-generation advanced satellite technologies in orbit Realization of small-scale, frequent scientific observation missions 06:10, August 24, 2005 (JST) Republic of Kazakhstan Dnepr (launched together with OICETS satellite) Weight Approx. 60 kg Dimensions 60 × 60 × 70 cm Perigee 610 km, Apogee 654 km 97.8

° Type of Orbit Period Near-circular orbit 97 min Scientific Instruments Star tracker Spin/non-spin type solar sensors (SSAS/NSAS) Geomagnetic Aspect sensor (GAS) Three-axis optical fiber gyro (FOG) Reaction wheel (RW) and magnetic torquer (MTQ) as actuators Multi-spectral Auroral Camera (MAC) Aurora particle observation instrument (Electron/Ion Spectrum Analyzer: ESA/ISA) Still operational on May 23rd 2008

26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Consequences of Auroral Acceleration

• Auroral Kilometric Radiation – Earth’s natural radio wave source – Frequency ~ electron cyclotron frequency – Current model: field-aligned beams of electrons form unstable distribution functions due to magnetic field convergence and mirror force

26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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AKR and radio emissions

• Laboratory experiments have confirmed that electrons travelling into a converging magnetic field form a horseshoe distribution function which is unstable to radio emissions near the electron cyclotron frequency

2008]

simulations

[McConville et al., PPCF 2008; Ronald et al., PoP

• Results consistent with 3D PIC

[Gillespie et al., PPCF 2008]

•

NB: no background plasma in lab

• Active experiments have artificially triggered AKR and observed significant density depletions [Wong et al., PRL 2009]

26 th August 2009

f ce

Figure 1, McConville et al., PPCF 2008

= 4.42GHz

Reporter Review: Div III Auroral Processes C. E. J. Watt Figure 8(b), McConville et al., PPCF 2008

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AKR fine structure

FAST data: Figure 1e, Su et al., [JGR 2008]: Alfvén waves Cluster data: Figure 1, Hanasz et al., GRL 2008]: Alfvén waves FAST & Cluster data: Figures 2&5, Pottelette & Pickett, [NPG 2007]: Phase space holes 26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Location of AKR

• Morioka et al.,

[JGR 2008; AG 2009]

use frequency of AKR to infer source altitude • Modelling

[Savilov et al., PoP 2007]

suggests that AKR could present with multiple frequencies – not just Ω ce – J || ↑, frequencies change • Better to use multiple spacecraft and ray-tracing to deduce the source location of AKR

[Mogilevsky et al., JETP 2007; Mutel et al., GRL 2008]

• Lab experiments also available • Can frequency alone determine source altitude?

Figure 1, Morioka et al., [AG 2009] 26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Consequences of Auroral Acceleration

• Ion Outflow and Upflow – Wave-driven (shear Alfvén waves) – Electron precipitation and electromagnetic Poynting flux – Ion heating (“pressure-cooker” effect)

26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Ion outflow and shear Alfvén waves

• Models of interaction between Alfvén waves and plasma which result in density cavities and upflowing ions: – Steepening nonlinear inertial Alfvén waves → ion cyclotron and ion acoustic waves → ion heating → upflow

[Seyler & Liu, JGR 2007]

– Ponderomotive force in the Ionospheric Alfvén Resonator

[Sydorenko et al., JGR 2008]

– Active ionospheric feedback and ponderomotive force

[Streltsov & Lotko, JGR 2008]

t=0 t=40s t=0 t=3min

Figure 7(e), Sydorenko et al., [JGR 2008] 26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt Figure 5, Streltsov & Lotko, [JGR 2008]

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Ion upflow and outflow

• Modelling of ion upflow/outflow, including electron precipitation, wave-particle interactions, heating, etc: – fluid kinetic model

[Zettergren et al., JGR 2007]

– dynamic fluid kinetic

[Horwitz and Zeng, JGR 2009]

– wave-particle interactions

[Barghouthi et al., JASTP 2008; Barghouthi, JGR 2008]

• Detailed observations: – SIERRA rocket

[Lynch et al., AG 2007]

– Incoherent scatter radar

[Zettergren et al., JGR 2008] 26 th August 2009 Ionospheric plasma parameters and model: Figure 10, Zettergren et al., JGR 2008

time (s)

Reporter Review: Div III Auroral Processes Figure 6, Lynch et al., AG 2007 C. E. J. Watt

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Substorm aurora: Large scale/low frequency undulations

• All the physical processes discussed previously apply to substorm aurora • Many repeatable features of substorm aurora that deserve particular study.

Figure 3, Keiling et al., [GRL 2008].

in-situ energetic ions Variations in large-scale brightening (21-24MLT) with same period as ion injection, ground Pi2

[Keiling et al., GRL 2008]

and boundary oscillation in space

[Keiling et al., JGR 2008]

auroral photon flux

26 th August 2009

Periodic bright spots related to an instability?

Figure 2, Henderson [AG 2009] Reporter Review: Div III Auroral Processes C. E. J. Watt

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raw difference

Substorm aurora: Expansion phase onset

Figure 2, Sakaguchi et al., AG 2009 All-sky TV camera (30Hz); 1s images 26 th August 2009 Figure 1, Liang et al., GRL 2008 THEMIS ASI: 3s images Reporter Review: Div III Auroral Processes C. E. J. Watt

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raw

Substorm aurora: Pi1/Pi2 waves and auroral onset

Figure 6, Rae et al., JGR 2009

• Substorm onset can manifest as undulations in aurora ( λ~10s of km) • Both undulations and large-scale auroral onset location are linked to magnetic perturbations in the Pi1/Pi2 wave bands difference

26 th August 2009 Figure 6, Murphy et al., JGR 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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dawn electron aurora

Solar-wind driven aurora

proton aurora dusk

Figure 2, Liou et al., JGR 2007 Figure 1 (a), Laundal & Østgaard, JGR 2007

• Proton and electron aurora show prompt and persistent response to high SW dynamic pressure

[Liou et al., JGR 2007; Laundal & Østgaard, JGR 2008].

• Compression of magnetosphere → changing mirror ratio → precipitaton • Dawn-dusk asymmetry suggests that gradient & curvature drift play a role

26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Aurora equatorward of traditional

• •

oval

• Isolated arcs equatorward of main auroral oval due to particle scattering by EMIC waves: – Protons: tens of keV [Yahnin et al., JGR 2007; Yahnina et al.,

JGR 2008; Sakaguchi et al., JGR 2008]

– Electrons: MeV [Miyoshi et al., GRL 2008] – All associated with ground-based wave observations in Pc1 band

Sandanger et al., [JGR 2007]

show that structure in the relativistic electron precipitation match structures in the anisotropic proton flux → EMIC wave precipitation

Jordanova et al., [JGR 2007]

present simulations of sub auroral arcs due to EMIC waves which compare favourably with observations.

Reporter Review: Div III Auroral Processes C. E. J. Watt 26 th August 2009

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Advances in Auroral Science methods

• Observations: – High temporal resolution ground-based imagers – Coverage over northern latitudes and many hours of MLT – High temporal resolution imagers with spectral resolution – Low-altitude spacecraft with imager & particle detection – Multi-spacecraft missions • Theory/simulation: – Generation and evolution of parallel electric fields – Non-uniform, non-periodic models – Active magnetosphere-ionosphere coupling • Active experiments: – Laboratory – Ionosphere/Magnetosphere

26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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Further information

• Reviews published 2007-2009 – Shear Alfvén waves in the magnetosphere

[Keiling, SSR 2009]

– Downward current region physics

[Marklund, SSR 2009]

– Laboratory experiments and space physics

[Koepke, RG 2008]

– Current-voltage relationship

[Pierrard et al., JASTP 2007]

– Fine structure of aurora

[Sandahl et al., JASTP 2008]

– Polar cap aurora

[Newell et al., JASTP 2009]

– EMIC waves and proton precipitation

[Yahnin & Yahnina, JASTP 2007]

– Artificial stimulation of IAR

[Yeoman et al., ASR 2008]

– Importance of auroral physics in the Universe

[Hultqvist, JASTP 2008]

• This review, and the bibliography, is available at: http://www.phys.ualberta.ca/~cwatt/reporter_review

26 th August 2009 Reporter Review: Div III Auroral Processes C. E. J. Watt

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