Relationship of Plasma Sheet and Plasma Sheet Boundary Layer to Auroras George K. Parks Space Sciences Laboratory University of California, Berkeley, CA Review Discuss Recent Observations Summary

Early Observations Central Plasma Sheet Gringauz et al., Soviet Astron, AJ 4, 680, 1961 Anderson, K., JGR 70, 4741, 1965 Bame et al, JGR, 72, 113, 1967 Frank, L., JGR. 72, 185, 1967 Plasma Sheet Boundary Layer Frank, L., Phys. Sol. Plan. Environ., 2, Eds. D. Williams, AGU, 1967 DeCoster and Frank, JGR, 84, 5009, 1979 Forbes et al., GRL, 8, 261, 1981 Eastman et al., JGR., 89, 1553, 1984 Takahashi and Hones, JGR 93, 8558, 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 in ions at CPS/PSBL Bursty bulk flow of ions in CPS Large in ions observed in PSBL Bursty Bulk Flows interpreted in terms of a tail merging model

Some questions about the large ion events Are bursty bulk flows really ExB flows in CPS? What phase space features are responsible for the large ion ?

Definitions Particle Measurements come from Electrostatic analyzers and Solid State Detectors Bulk Plasma Parameters (Computed quantities) =  f(r, v; t) d 3 v =  v f (r, v; t) d 3 v =  (v i - )(v j - ) f (r, v) d 3 v Working Definition of CPS (Angelopoulos et al., 1992) B xy 0.5

Field-aligned beams in PSBL Moments of the df and B Pitch-angle spectrogram

Examples of High 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 B x = B o tanh (z/L) N = N o /cosh 2 (z/L) Initial condition: Maxwellian distribution with T cutoff at 0.75 V ti (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 does not mean the plasma is flowing. High can result near thin boundaries because of remote sensing effects. High does not mean the plasma is flowing. Even stationary plasma can yield high because of finite gyroradius effects. It is important to examine the phase space distribution before concluding there is high speed flows because 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