1. Mass Transport: To the Plasma Sheet – and Beyond!
Terry Onsager, Joe Borovsky, Joachim Birn, and many friends
• Transport into the Plasma Sheet
• Transport within the Plasma Sheet
• Transport from the Plasma Sheet into the Inner Magnetosphere
Where does the plasma sheet come from, and why does it have the properties it has?

2. Transport – is a topic proposed for a new GEM campaign
We propose that within this campaign, a working group be devoted to modeling mass transport into, within, and from the plasma sheet.
Modeling the plasma sheet presents an opportunity to test our knowledge of processes occurring throughout the magnetosphere and ionosphere, and it is an obligation in order to fulfill GEM’s goals.
• Plasma Sheet has a dominant role in magnetospheric dynamics
• It is a relatively slowly varying integrator of numerous source, loss, and transport processes.
• It provides an opportunity to test our understanding magnetosheath, boundary layer, ionospheric, and magnetotail processes.
• It is a conduit for mass into the inner magnetosphere.
• Global magnetospheric models are running and increasingly relied on. The plasma sheet is a critical element of these models, and it valuable location to test our understanding and to and guide further research.

4. Magnetopause and Boundary Layers for Southward IMF
Cusp
Magnetopause
LLBL
Mantle
Polar
Rain
Lobe
Plasma Sheet
Lobe

5. Convection Paths for IMF Bz < 0
Lockwood, 1995
• Closed magnetic field convects outward to the magnetopause and interconnects with magnetosheath field.
• Magnetospheric, ionospheric, and magnetosheath plasma flows freely into and out of the magetosphere across the open regions of the magnetopause.
• Open field lines convect over the poles and into the magnetotail.

6. Pilipp and Morfill, 1978
Particle with low parallel speed
Particle with high parallel speed
• Magnetosheath plasma continuously crosses the magnetopause boundary and convects toward the plasma sheet as it flows tailward.
• The distribution of parallel velocities and the ExB drift speed control the plasma content on field lines that reconnect in the tail.
• Plasma heating occurs in the current sheet on the newly closed field lines.
• Near-Earth reconnection can trap solar wind plasma in the near-Earth plasma sheet, even though convection in the distant plasma sheet may be tailward.

7. Observed at FAST Inferred
Joule Dissipation
Electron Heating/Ionization
Electron Scale Height
Increased Ambipolar Field
Ion Scale Height
Increase
Ion Upwelling
ELF/VLF Waves
(Heating)
Electron Precipitation
(Magnetosheath)
Poynting Flux
Ion Outflow
Alfven Waves
Causal
Possible Causal
Correlated
Inferred
Observed at FAST
T. Abe
Various electron, ion, and electrodynamic process are responsible for heating and accelerating ionospheric plasma.
Bob Strangeway

8. Transport of Ionospheric Plasma to the Magnetotail
Thermal cusp H+ (15 eV) are lost downtail
Thermal O+ from the cusp and H+ from the nightside auroral zone are energized in the plasma sheet
Thermal O+ from the nightside auroral zone receive little energy
Dayside auroral outflow (500 eV) is lost downtail.
Most H+ are lost downtail.
Nightside auroral O+ outflow is energized in the plasma sheet.
Delcourt et al., 1990; 1993

9. • H+ outflow rate increases by about a factor of 4 from Kp = 0 to 6.
H+ and O+ outflow rates ( keV) integrated over all MLT and all latitudes about 56º
Yau et al., 1988
• H+ outflow rate increases by about a factor of 4 from Kp = 0 to 6.
• O+ outflow rate increases by about a factor of 20 from Kp = 0 to 6.
• H+ outflow rate is independent of solar activity level (F10.7).
• O+ outflow rate increases with increasing solar activity.

10. • Flux of ionospheric ions is not strongly correlated with IMF Bz
• Flux of ionospheric ions is strongly correlated with variation in solar wind dynamic pressure
• Flux of ionospheric ions is not strongly correlated with IMF Bz
Moore et al., 1999; Elliott et al., 2001

11. Convection Paths for IMF Bz > 0
Lockwood, 1995
• High latitude lobe and plasma sheet field lines convect to the magnetopause and reconnection with magnetosheath field lines poleward of the cusp.
• Magnetopause crossing point of the new lobe field line moves downtail.
• New lobe field line eventually returns to the dayside magnetopause and continues the lobe-cell circulation.
• No contribution to filling the plasma sheet results.

12. Capture of Magnetosheath Plasma for IMF Bz > 0
• If reconnection occurs at high latitudes, new closed field lines will be formed with a mixture of magnetosheath and magnetospheric plasma.
• Reconnection has been shown to occur first in one hemisphere and then the other, not simultaneously in the two hemispheres.
• Reconnection occurs over a large local-time range on the magnetopause, even though the ionospheric footprint could be small.
Song and Russell, 1992

13. Convection Paths for IMF Bz > 0
Lockwood, 1995
• High latitude lobe and plasma sheet field lines convect to the magnetopause and reconnection with magnetosheath field lines poleward of the cusp in both hemispheres.
• The subsequent convection of the new closed flux tube into the magnetotail is not well known, but may be an important source of the plasma sheet.

14. MHD Simulations of Plasma Sheet Filling with IMF Bz > 0
Closed Magnetic
Topology
Raeder et al, 1995
80 minutes after northward IMF turning
225 minutes after northward IMF turning
• New closed field lines form through high-latitude magnetopause reconnection.
• Boundary layer plasma convects tailward and toward the tail center.
• Open tail flux becomes narrowly confined to the center of the tail as the boundary layer expands.

15. Geotail Observations of Plasma Sheet Density and Temperature
Terasawa et al., 1997
• Northward IMF: High density and low temperature
• Southward IMF: Low density and high temperature

16. Wind Observations of Plasma Sheet Density Versus IMF Theta Angle
Cold, Dense Plasma Sheet:
Ne > 0.7; Te < 200 eV
• Cold, dense plasma sheet forms after prolonged northward IMF.
• Cold, dense plasma sheet is observed on the dawn and dusk flanks.
Oieroset et al., 2003

17. • Reconnection within the vortices is responsible for mass transport.
Geotail observed the flank LLBL ~13-15 RE downtail over ~ 5 hours with steady IMF Bz > 0.
Fairfield et al., 2000; Otto and Fairfield, 2000
• Comparison of plasma and field fluctuations observed and from 2-D MHD simulation results showed strong agreement.
• Vortices require several minutes to form. They form at X ~ -15 RE, and have a size of about 2 RE.
• Reconnection within the vortices is responsible for mass transport.
• Recent article argues against mass transport by this process [Stenuit et al., 2002].

18. • Geotail led Wind by about 5 RE in the cross-tail direction.
• Geotail and Wind crossed the magnetotail at a downtail distance of about RE.
• Geotail led Wind by about 5 RE in the cross-tail direction.
• Geotail and Wind simulaneously measured the increase in plasma sheet density and decrease in temperature as the IMF became northward.
• This observation may indicate that the change in plasma sheet is moving down the tail, rather than across the tail from the flanks.
8 hr
Oieroset et al., 2003

19. Borovsky et al., 1998

21. Fuselier et al., 1999

22. Modeled Storm Magnitude Depends on Plasma Sheet Density
Nps fixed at pre-storm value
Nps variation in RAM
as observed by LANL GEO
Kozyra et al., 1998

23. Modeled Storm Magnitude Depends on Plasma Sheet Temperature
Ebihara and Ejiri, 2000

24. • Radiation belt electrons exhibit abrupt enhancements and loss driven by the solar wind and magnetospheric conditions.
• Radiation belt loss occurs with the onset of geomagnetic activity following a period of prolonged quiet.
• Loss initiates with strong distortion of the inner magnetospheric magnetic field, and may be due to the sunward convection of a cold, dense plasma sheet.
Janet Green

25. • Geosynchronous Orbit:
3x10-9
Geosynchronous
Orbit
M = 2100 MeV/G
ISEE 1
11 RE Downtail from Earth
Hilmer et al., 2000
• Plasma Sheet:
Williams et al., 1990
• Plasma sheet electron and ion heating was associated with current sheet disruption and field dipolarization.
• Phase space density in the near-Earth plasma sheet is comparable to phase space density at geosynchronous orbit.
• Geosynchronous Orbit:

26. Summary
• The plasma sheet is the place through which mass flows: from the solar wind and the ionosphere, then into the inner magnetosphere and out to the solar wind.
• Plasma transport and heating are influenced by the IMF, with transport time scales typically longer than time scales of IMF variability.
• Southward IMF leads to a hot and tenuous plasma sheet.
• Northward IMF leads to a cold and dense plasma sheet.
• Both solar wind and ionospheric plasma contribute importantly to the plasma sheet, yet the variability in the relative fraction is not known.
• Understanding transport from the ionosphere and from the magnetosheath is critical to understanding the plasma sheet.
• Understanding the plasma sheet it critical to being able to understand and model the inner magnetosphere.
• GEM should take the challenge to model geospace transport, with modeling the plasma sheet as one specific goal to demonstrate our understanding.