Relationship of Plasma Sheet and Plasma Sheet Boundary Layer to Auroras

George K. Parks

Space Sciences Laboratory

University of California, Berkeley, CA 94720

• Review

• Discuss Recent Observations

• Summary

Early Observations

Central Plasma SheetGringauz et al., Soviet Astron, AJ 4, 680, 1961

Anderson, K., JGR 70, 4741, 1965Bame et al, JGR, 72, 113, 1967Frank, L., JGR. 72, 185, 1967

Plasma Sheet Boundary LayerFrank, L., Phys. Sol. Plan. Environ., 2, Eds. D. Williams, AGU, 1967

DeCoster and Frank, JGR, 84, 5009, 1979Forbes et al., GRL, 8, 261, 1981Eastman et al., JGR., 89, 1553, 1984Takahashi and Hones, JGR 93, 8558, 1988.M. Nakamura et al., JGR, 96, 5631, 1991

A Schematic diagram of boundary layers(Eastman et al., JGR 90, 9541, 1985)

Based on ion measurements

Connection to Electron Precipitation and Aurora

J. Heppner et al., JGR 72, 5417, 1967

E. Hones et al., JGR 73, 1968

G. Parks and J. Winckler, JGR 73, 5786,1968

J. Hargreaves et al., Proc. Int. Symp. On Sol-Terr. Phys., San Paolo, Brazil, 1974

J. A. Sauvaud et al., JGR 92, 2365, 1987

Parks and Winckler (1968)

ATS-1 Energetic Electrons

ATS-1 magnetic field

College magnetogram

ATS-1 Energetic Electrons

Bremsstrahlung X-rays

Substorm behavior at synchronous altitude and plasma sheet(Sauvaud et al., 1987)

Large <v> in ions at CPS/PSBL

Bursty bulk flow of ions in CPS

Large <v> in ions observed in PSBL

Bursty Bulk Flows interpreted in terms of a tail merging model

Some questions about the large ion <v> events

Are bursty bulk flows really ExB flows in CPS?

What phase space features are responsible for

the large ion <v>?

Definitions

Particle Measurements come from Electrostatic analyzers and Solid State Detectors

Bulk Plasma Parameters (Computed quantities)

< n > = f(r, v; t) d3v

< v > = v f (r, v; t) d3v

< v2> = (vi - <v>)(vj - <v>) f (r, v) d3v

Working Definition of CPS (Angelopoulos et al., 1992)

Bxy < 15 nT, Bx/Bxy > 0.5

Field-aligned beams in PSBL

Moments of the df and B

Pitch-angle spectrogram

Examples of High <v> events (BBF) (March 27, 1996 studied by Angelopoulos et al., 1997)

Conjunction event with UVI(July 29, 1996 event studied by Fillingim et al., 27, 1379, 2000)

Relationship of pseudo breakup and substorm expansion

Pi-2 near footprint of WIND

Pseudo breakups and substorm expansion in PS and PSBL

Distribution Function and Energy Spectra

High time resolution plots during pseudo breakups

What we learned about pseudobreakups and substorms

Cluster current sheet crossings on October 1, 2001 (Runov et al., 2003)

Thin Current Sheet

During periods of strong geomagnetic activity, the current sheet can thin to ion gyroradius scales (Mitchell et al., 1990).

Particles can gain energy by nonadiabatic motions allowing traversal across tail electric field (Speiser orbits).

Strong gradients can lead to nongytropic ion distributions due to “remote sensing” effects (Williams, 1980; Marcucci et al., 2004) which have been used to estimate magnetotail motions and plasma sheet orientations (Owens et al.,1995).

Ampte observations of nongytropic magnetotail ions were interpreted as signatures of gyrophase bunching (Nakamura et al., 1991).

Geotail observed nongytropic ion distributions intepreted them as a mixture of different sources and acceleration histories (Mukai et al., 1998)

Examples of Distribution function(Wilber et al., 2004)

Test particle simulation(Lee et al., GRL 31, Dec 2004)

Harris current sheet

Bx = Botanh (z/L)

N = No/cosh2 (z/L)

Initial condition: Maxwellian distribution with T cutoff at 0.75 Vti (observed)

z/L position wrt current sheet

i/L kinetic effects with finite Larmor radii effect

Remote Sensing Effects

Thick current sheet

Thin current sheet

model

Summary

High <v> does not mean the plasma is flowing.High <v> can result near thin boundaries

because of remote sensing effects.High <v> does not mean the plasma is flowing.Even stationary plasma can yield high <v>

because of finite gyroradius effects.It is important to examine the phase space

distribution before concluding there is high speed flows because <v> is large.

Many problems still to be studied.

Origin of the beams in the PSBL?Distinguish observationally whether a substorm

is due to onset of a tearing mode instability or current disruption (ballooning mode)?

Role of electrons in the overall dynamics?Requirements for the plasma and particle

instruments to resolve some of the observational issues?

The End