F. Plaschke, V. Angelopoulos

IGPP, UCLA

March 23, 2012 - THEMIS SWT meeting, UCLA

Magnetopause surface waves: A THEMIS case

compared to MHD theory

MP surface waves: A THEMIS case compared to MHD theory

MP surface waves

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B

V

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Eflux

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2011 Oct 06

MP surface waves: A THEMIS case compared to MHD theory

THEMIS configuration

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MP

THEMIS

wave

MP surface waves: A THEMIS case compared to MHD theory

THEMIS configuration

3

MP

THEMIS

MP

THA THD THE

flow

wavewave

wave

MP

cross-correlationphase speed

comparison with MHD

wave formand structure

MP surface waves: A THEMIS case compared to MHD theory

MHD theory

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evanescentwaves

MP

k2N =!2

V 2A + C2

S⌦2/!2

� k2t

⌦2 = !2 � (~k · ~VA)2

ptot,a = p

tot,b

⇠N,a = ⇠N,b

!a = !b � ~kt · ~v0,a

kN,a

⇢0,a⌦2a

=kN,b

⇢0,b⌦2b

vph =!b

kt=

⇢0,a(~nkt · ~v0,a)⇢0,a + ⇢0,b

±

s⇢20,a(~nkt · ~v0,a)2

(⇢0,a + ⇢0,b)2+

⇢0,a(~nkt · ~VA,a)2

⇢0,a + ⇢0,b+

⇢0,b(~nkt · ~VA,b)2

⇢0,a + ⇢0,b� ⇢0,a(~nkt · ~v0,a)2

⇢0,a + ⇢0,b

boundary conditions

magnetosonic dispersion relation

doppler shift

surface wave dispersion relation

solution for incompressible plasmas

MP surface waves: A THEMIS case compared to MHD theory

Comparison with MHD theory

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PDL

LLBL

magnetosphere

magnetosheath ✔✘

parameters velocity wave modes

✘ ✔slow

stability

KHI✘

✔

wave

sheath

results of comparison

kN,a

⇢0,a⌦2a

=kN,b

⇢0,b⌦2b

surface wave dispersion relation

parameter study:balance sides of dispersion relation

magnetosheath and magnetospheric measurementspossible imaginary frequency component

MP surface waves: A THEMIS case compared to MHD theory

Wave form - plasma velocity

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LLBL

PDL PDL

LLBL

wave

PDL

plasma flow in wave‘s frame of reference

sheath

LLBL

wave

wave

MP surface waves: A THEMIS case compared to MHD theory

Wave form - plasma velocity

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LLBL

PDL PDL

LLBL

wave

PDL

plasma flow in wave‘s frame of reference

sheath

LLBL

wave

acceleration: Chen and Kivelson (1993)

wave

MP surface waves: A THEMIS case compared to MHD theory

Wave form - plasma velocity

6

LLBL

PDL PDL

LLBL

wave

PDL

plasma flow in wave‘s frame of reference

sheath

LLBL

wave

deceleration?

wave

MP surface waves: A THEMIS case compared to MHD theory

Phase vs. magnetosheath velocity

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vph =!b

kt=

⇢0,a(~nkt · ~v0,a)⇢0,a + ⇢0,b

±

s⇢20,a(~nkt · ~v0,a)2

(⇢0,a + ⇢0,b)2+

⇢0,a(~nkt · ~VA,a)2

⇢0,a + ⇢0,b+

⇢0,b(~nkt · ~VA,b)2

⇢0,a + ⇢0,b� ⇢0,a(~nkt · ~v0,a)2

⇢0,a + ⇢0,b

solution for incompressible plasmas

MP surface waves: A THEMIS case compared to MHD theory

Phase vs. magnetosheath velocity

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magnetosheath velocity

phas

e ve

loci

ty

KHI

vph =!b

kt=

⇢0,a(~nkt · ~v0,a)⇢0,a + ⇢0,b

±

s⇢20,a(~nkt · ~v0,a)2

(⇢0,a + ⇢0,b)2+

⇢0,a(~nkt · ~VA,a)2

⇢0,a + ⇢0,b+

⇢0,b(~nkt · ~VA,b)2

⇢0,a + ⇢0,b� ⇢0,a(~nkt · ~v0,a)2

⇢0,a + ⇢0,b

solution for incompressible plasmas

MP surface waves: A THEMIS case compared to MHD theory

Phase vs. magnetosheath velocity

7

magnetosheath velocity

phas

e ve

loci

ty

KHI

observed wave

vph =!b

kt=

⇢0,a(~nkt · ~v0,a)⇢0,a + ⇢0,b

±

s⇢20,a(~nkt · ~v0,a)2

(⇢0,a + ⇢0,b)2+

⇢0,a(~nkt · ~VA,a)2

⇢0,a + ⇢0,b+

⇢0,b(~nkt · ~VA,b)2

⇢0,a + ⇢0,b� ⇢0,a(~nkt · ~v0,a)2

⇢0,a + ⇢0,b

solution for incompressible plasmas

MP surface waves: A THEMIS case compared to MHD theory

Our future work

• Surface wave evolution along MP.

• Coupling to inner magnetospheric waves.

• Wave deceleration.

• Steepening (non-linear behavior).

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