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?

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.

Magnetopause and Boundary Layers for Southward IMF

Cusp

Cusp

Magnetopause

LLBL

Mantle

Mantle

PolarRain

PolarRain

Plasma Sheet

Lobe

Lobe

• 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.

Convection Paths for IMF Bz < 0

Lockwood, 1995

• 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.

Particle with low parallel speed Particle with high parallel speed

Pilipp and Morfill, 1978

Joule Dissipation Electron Heating/Ionization

Electron Scale HeightIncreased Ambipolar Field

Ion Scale HeightIncrease

Ion Upwelling

ELF/VLF Waves(Heating)

Electron Precipitation(Magnetosheath)Poynting Flux

Ion Outflow

Alfven Waves

Causal Possible Causal Correlated

Infe

rred

Obs

erve

d at

FA

ST

Bob Strangeway

T. Abe

Various electron, ion, and electrodynamic process are responsible for heating and accelerating ionospheric plasma.

Transport of Ionospheric Plasma to the Magnetotail

• Dayside auroral outflow (500 eV) is lost downtail.

• Most H+ are lost downtail.

• Nightside auroral O+ outflow is energized in the plasma sheet.

• 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

Delcourt et al., 1990; 1993

Yau et al., 1988

H+ and O+ outflow rates (0.01-17 keV) integrated

over all MLT and all latitudes about 56º

• 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.

• 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

• 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.

Convection Paths for IMF Bz > 0

Lockwood, 1995

Song and Russell, 1992

• 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.

Capture of Magnetosheath Plasma for IMF Bz > 0

• 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.

Convection Paths for IMF Bz > 0

Lockwood, 1995

Raeder et al, 1995

MHD Simulations of Plasma Sheet Filling with IMF Bz > 0

80 minutes after northward IMF turning 225 minutes after northward IMF turning

Closed MagneticTopology

• 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.

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

• Cold, dense plasma sheet forms after prolonged northward IMF.

• Cold, dense plasma sheet is observed on the dawn and dusk flanks.

Wind Observations of Plasma Sheet Density Versus IMF Theta Angle

Cold, Dense Plasma Sheet:Ne > 0.7; Te < 200 eV

Oieroset et al., 2003

• 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].

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

• Geotail and Wind crossed the magnetotail at a downtail distance of about 15 - 20 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 hrOieroset et al., 2003

Borovsky et al., 1998

Fuselier et al., 1999

NNpsps fixed at pre-storm value fixed at pre-storm value

NNpsps variation in RAM variation in RAM

as observed by LANL GEOas observed by LANL GEO

Modeled Storm Magnitude Depends on Plasma Sheet Density

Kozyra et al., 1998

Ebihara and Ejiri, 2000

Modeled Storm Magnitude Depends on Plasma Sheet Temperature

• 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

3x10-9

GeosynchronousOrbit

M = 2100 MeV/G

ISEE 111 RE Downtail from Earth

• 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.

• Plasma Sheet:

639

631022

3

103

1066.1

/2800

kms

kmscp

jmf

GMeVM

e

• Geosynchronous Orbit:

63893 10103

/2100

kmsmf

GMeVM

e

Hilmer et al., 2000

Williams et al., 1990

• 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.

Summary