a role of transient dipolarizations in the magnetotail energy...

A Role of Transient Dipolarizationsin the Magnetotail Energy

ConversionUCLA

Andrei Runov

Thanks to V. Angelopoulos and THEMIS teamA. Artemyev, J. Birn, C. Gabrielse, M. Hesse, J. Liu, D.L. Turner, X.Z. Zhou

&NASA contract NAS5-02099, grants NNX13AF81G, and NNX16AF84G

SHIELDS Workshop, Santa Fe, NM, April 4, 2016 [email protected] 1

Transient Dipolarizations and Flux Transport:an Example of THEMIS Observations

• Arbitrary chosen example• OMNI Integrated Electric Field• THEMIS

D[-10.5, 3.5] and E[-10.3, 4.5] RE :I Bx (blue); By (green); Bz (red)I Ey = −[V × B]y

• Transient response:Pulses of magnetic flux transportwith a characteristic time of 30 -100 s.

• Rapid Flux Transport (RTF) events(Schoedel et al., 2001)

• Dipolarizing Flux Bundles (DFBs)(J. Liu et al., 2013)

• Typical behavior, see, e.g.,Angelopoulos et al., Science 2013for similar example.

∫Ey d

t

SW IMF

∫VxBzdt

B,

nT

Ey,

mV

/m

THE

THD X, Y, Z

THE

THD

OMNI


RFT/DFB THEMIS Statistics

R

RTF/DFB Scales

After J. Liu et al. (2013)

Reconnection Ejecta

From Birn et al., 2014

~2 RE

~2 RE

Birn et a., 2014: MHD withη = η0/cosh

2( xLx ,yLy

, zLz ),Ly = 8

• Spatially localized electric field(magnetic flux transport)enhancement;

• Scale: ∼2×2RE ∼30×30 c/ωpi• Why do we care?


Conceptual Cartoons

E

DUSK

BEARTH

e-

e-Te1>Te0

Te0

E

DUSK

BEARTH

i+

i+

Ti0

Ti1>Ti0

ELECTRONS

IONS

Birn et al. (2012); Gabrielse et al. (2012);Runov et al. (2013)

• Contracting dipolarized fluxtube;

• Bz enhancement within an areaA: a localized enhancement inthe magnetic flux through theequatorial plane

Φ=∫A B.dA ∼10 nT.10

8 km2 ∼1011 Wb• E pulse in the stationary FOR

⇒ Interaction with ambientparticles: energization

Ey ∼1 - 5mV/m; ∆Y ∼107m⇒ ∆U = Ey .∆Y ∼10 - 50 keV

• Continuous EM energyconversion into thermalenergy of the ambientplasma

δE ∼ 1µ0

EyBz ∼109 - 1010 J/R2E/s;τ ∼100 s ⇒ 10 - 100GJ/R2E


Test Particle Simulations

From Birn et al. SSR, 2012

• Correlation between background and DFB ion and electron temperatures• Hotter electrons on the dawn; hotter ions on the dusk side;• Do we observe this?


Tin/Tbg Correlation; Te/Ti Ratio (Runov et al., 2015)

0 5 10 15 20 25 30Ti_bg, keV

0

5

10

15

20

25

30

Ti_

int,

ke

V

cc=0.72(0.77)cc=0.74(0.70)cc=0.59(0.50)cc=0.76(0.67)

Ti_in=1.82+1.15*Ti_bg

0 5 10 15 20 25 30Te_bg, keV

0

5

10

15

20

25

30

Te

_in

,ke

V

cc=0.77(0.74)cc=0.59(0.59)cc=0.73(0.77)cc=0.58(0.56)

Te_in=0.36+1.63*Te_bg

background population

0 5 10 15 20 25 30Ti, keV

0

5

10

15

20

25

30

Te

,ke

V

intruding population

0 5 10 15 20 25 30Ti, keV

0

5

10

15

20

25

30

Te

,ke

V

T1

T2

T3

T1

T2

T3

Ti=7Te

Ti=7Te


Test Particle Simulations: Ions

From Birn et al. JGR, 2015


Ti ,e(Bz) Correlation and Linear Regression

• µi,e ≈ constant (e.g., Birn et a., 2015) ⇒ Ti,e ∝ Bzα, α ∼1

intruding ions

0.1 1.0 10.0 100.0Bz, nT

0.1

1.0

10.0

100.0

Ti,

ke

V

Ti=1.48*Bz^0.8

cc=0.42

intruding electrons

0.1 1.0 10.0 100.0Bz, nT

0.1

1.0

10.0

100.0

Te

,keV

Te=0.13*Bz^1.3

cc=0.47


Ion and Electron Spectra: J(E) = n(

Em2

)(m

πκE0

)3/2 Γ(κ+1)Γ(κ−1/2)

(1 + E

κE0

)−κ−1background population, ions

102 103 104 105

Energy, eV

102

103

104

105

106

107

DifferentialEnergyFlux,eV/cm^2

/s/sr/eV

kappa=6.5±1.0kappa=5.5±0.5kappa=6.5±1.0kappa=6.0±1.5

background population, electrons

102 103 104 105

Energy, eV

102

104

106

108

DifferentialEnergyFlux,eV/cm^2

/s/sr/eV


intruding population, ions

102 103 104 105

Energy, eV

102

103

104

105

106

107

DifferentialEnergyFlux,eV/cm^2/s/sr/eV


intruding population, electrons

102 103 104 105

Energy, eV

102

104

106

108

DifferentialEnergyFlux,eV/cm^2/s/sr/eV



Shabansky-type Interaction with Ambient Ions


Precoursor Ion Flux in Test-Particle Simulations

From Birn et al., (2015)see also Artemyev et a., (2015)

• FBs convert EM energy into thermal and mechanical energyof ambient plasma by

I pick up ambient particles via E = V × B;I Shabansky-type ion reflection on the FB (dipolarization/jet)

front.


Are FB Associated With Substorm (AL) Onset?

dt, s

1

min


Summary

• Earthward moving transient dipolarizations (RFT/DFB) serveas energy converters that convert the electromagnetic energyinto the thermal and mechanical energy of ambient particles;

• They may be thought as elementary building blocks (afterSergeev et al. 1996) of magnetotail activity;

• 3-D effect.


Open Questions

• FBs at R

a role of transient dipolarizations in the magnetotail energy...

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