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GENERATION OF DENSITY IRREGULARITIES IN THE PLASMASPHERE

Evgeny MishinBoston College ISR

MURI Workshop

3-6 March 2008

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OUTLINE

Introduction: Inner magnetosphere

Sub-Auroral PPolarization SStreams & Ion Drifts (SAPS & SAID)

SAPS/SAID-related plasmaspheric structures

Shear-flow and gradient-drift instabilities

APPROACH

•Compare plasmaspheric density structures with enhanced subauroral electric field

•Specify possible instabilities

OBJECTIVE: Specify the ducts formation conditions

Why should one care? Necessary for VLF triggering

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Inner Magnetosphere

Inner magnetosphere: Plasmasphere &

Ring Current

Driven byDriven by the magnetospheric convection electric fieldconvection electric field generated by the solar wind- magnetosphere interaction

A schematic diagram of the Earth’s magnetosphere

Usually described by the cold plasma drift approximation: Balance of the convection and convection and corotation electric fieldscorotation electric fields

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Large-Scale Structures: SAPS

During magnetic (sub)storms energetic particles are injected into the plasmasphere forming the “partial” ring current at dusk

Plas

ma

shee

t bou

ndar

y

Upward (Region 1) & downward (Region 2) FACs enhance.

Subauroral poleward electric fields appear enhanced westward convection (SAPS/SAID).

Topside Ionosphere: 850 km

~1 RE

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Middle-Scale Structure: SAID

08-Apr-2004 SAID event 50 min after onset

Puhl-Quinn et al., 2007+

C1 & F16: Magnetically conjugate within 0.2o

DMSP F16

PP

ause

C1

C4

<1000 km

Pla

sm

a s

he

et

bo

un

da

ry

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Middle-Scale SAPS Wave (sub) StructuresWave (sub) Structures (SAPSWSWS)

Conjugate DMSP observations show that after subsequent onsets SAPSWS enhance and move equatorward.

Short-scale e.m. field oscillations fade away during the substorm recovery.

Onsets at 1555 and 1710 UT

The outbound portion of CRRES orbit 765: The beginning of the 4-5 June 1991 storm

SAPSWS

8 min after the substorm onset

mV/m40

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Middle-Scale Structures: Plumes & Shoulders

Volland-Stern

IMAGE EUV image : PS equatorial cross-section

00

06

12

18

plu

me

1-2 RE

Including SAPS [Khazanov+]

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SAPSWS and Plasmaspheric Irregularities

Pla

sma

Sh

eet

bou

nd

ary

Ele

ct

Ion

s

diamagnetic current

CRRES orbit 766 during the main phase on 5 June 1991

ion and electron fluxes at pitch angles near 90o

plume

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SAID & Plasmaspheric troughAdrian et al. [ 2007]

Simulated equatorial density distribution containing a SAID generated trough

Simulated EUV image

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SAID & Plasmaspheric Irregularities

SAID 08-Apr-2004

Co-located with the SAID E-field variations

Strong shear flow: dVW/dr ~ 0.2 s-1 ~1/20 H+-gyrofrequency

Mishin et al., 2008

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SAID & Plasmapause & Auroral Boundary Mishin and Puhl-Quinn, GRL2007

18 March 2002 25 min after onset DMSP F14

The outer side of the SAID channel is aligned with the plasmapause and its outer edge marks the electron precipitation (auroral zone) boundary.

The overall SAID features agree with a short-circuiting of the substorm-injected plasmoid over the plasmasphere and the formation of a turbulent boundary layer.

PP

ause

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SAID and Plasmasphere’s Structuring

Cluster observations in the SAID system of reference

diamagnetic current near the inner edge

The short-circuit system in the plasmasphere extends far ahead the SAID channel

Mishin and Puhl-Quinn, GRL2007

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The current-convective instability in the RC- plasmasphere overlap

|| ||' /( )ek j en

Volkov& Maltsev, 1986

(static approximation)

|| ||' /( )e Dk j en k U Plasma cloud’s

transverse motion favors generation of

short-scale modes

Rise time a few min

Doppler-shifted frequency

1414

Density irregularities from Cluster

CLUSTER, 11- Apr-2002, 2130 MLT, Kp=3

Darrouzet et al., 2004

Cluster electron density profiles in the plasmasphere

IN OUT

plu

me

plu

me

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Motion of Plumes

cosn RV V

Darrouzet et al., 2004

The radial boundary velocity VR=(R1-R2)/(t1-t2)

The normal boundary velocity

( ) ( )sin (4 5)cor obsn cor nV V V

Co-rotation speed Vcor=0.47· Requat km/s

Shear flows near the plume

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Plasmapause & Electron Injection boundary

IMAGE/FUV electron aurora images.

The color is proportional to brightness of the detected auroral emissions.

The FUV images mapped to the equatorial plane:

The EUV determined plasmapause is overlaid on the mapped images.

IMAGE/FUV measurements of the substorm of 1900–2038 UT on 17 April 2002.

Goldstein et al., 2005

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Motion of Irregularities inside the PSDarrouzet et al., 2004

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SUMMARY

• Substorm injections generate highly-structured electromagnetic fields (SAPSWS) in the RC-plasmasphere overlap.

•SAPSWS generate small-scale density ducts inside the plasmasphere.

•Plasmaspheric irregularities develop shortly after the substorm injection front arrives at the plasmapause.

•SAPS/SAID define the outer boundary (plasmapause) of the perturbed plasmasphere and create strong shear flows.

•Irregularities inside the plasmasphere last for a few hours, virtually co-rotating.

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Stationary Conditions

The subscript S refers to a stagnation point in cold plasma drift.

convection

corotation

Ly and PC are defined by the solar wind pressure and IMF

Zero-order, cold plasma drift approximation (Volland-Stern) separatrix

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SAPSWS- (cont’d)

The outbound portions of CRRES orbits 765 (onset), 766 (middle of the 1st main phase) and 767 (middle of the 2nd main phase) on 5 June 1991

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Plasmapause & RB boundary

(a) SAMPEX high-energy (2–6 MeV) electrons, vs. L and day of year 2001.

Four main bursts of enhanced outer belt flux are labeled (‘1’ through ‘4’).

(b) Dst index, showing 4 main (‘1’–‘4’) and disturbances.

2–6-MeV, monthly window-averaged electron fluxes from SAMPEX (600 km)

The white curve represents every 10-day’s minimum Lpp based on the CRRES empirical model

Goldstein et al. [2005]

Li et al. [2006]

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Plasmapause & RB boundary (cont’d)

Red (Lmin) and blue (Lavg) dots respectively give 3.5-day running average of minimum and mean per-image plasmapause Lp.

Blue line (LMAX): L of peak flux.

Red line (L-1): 0.1 of peak flux.

IMAGE/EUV plasmapause data

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Structured precipitation from RB at HAARP[Pedersen et al., JGR, 2007]

Co-rotating, several-km-scale optical structures (‘angels dancing on the head of a pin’)

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SAPS & RB boundary at HAARP

Substorm onset at 04:50-UT

[Pedersen et al., JGR, 2007]

Background-subtracted negative all-sky 557.7-nm images mapped to geographic coordinates and superimposed with tracks for various satellite passes.

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SAPS & RB boundary at HAARP (cont’d)

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SAPS/SAID, RB boundary & Plasmapause

RB region

Similarities between Cluster and DMSP/NOAA observations