Mass Transport: To the Plasma Sheet – and Beyond! Terry Onsager, Joe Borovsky, Joachim Birn, and many friends • Transport into the.
Download ReportTranscript Mass Transport: To the Plasma Sheet – and Beyond! Terry Onsager, Joe Borovsky, Joachim Birn, and many friends • Transport into the.
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 Mantle Lobe Cusp Polar Rain LLBL Cusp Plasma Sheet Polar Rain Lobe Mantle Magnetopause 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. 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. Observed at FAST Alfven Waves Ion Outflow Electron Precipitation (Magnetosheath) Poynting Flux ELF/VLF Waves (Heating) Inferred Ion Upwelling T. Abe Ion Scale Height Increase Joule Dissipation Causal Bob Strangeway Electron Scale Height Increased Ambipolar Field Electron Heating/Ionization Possible Causal Correlated Various electron, ion, and electrodynamic process are responsible for heating and accelerating ionospheric plasma. 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 H+ and O+ outflow rates (0.01-17 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. • 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 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. 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 localtime range on the magnetopause, even though the ionospheric footprint could be small. Song and Russell, 1992 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. 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. 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 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 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]. • 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. Oieroset et al., 2003 8 hr Borovsky et al., 1998 Fuselier et al., 1999 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 Modeled Storm Magnitude Depends on Plasma Sheet Temperature Ebihara and Ejiri, 2000 • 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 M = 2100 MeV/G 3x10-9 Geosynchronous Orbit Hilmer et al., 2000 ISEE 1 11 RE Downtail from Earth Williams et al., 1990 • Plasma sheet electron and ion heating was associated with current sheet disruption and field dipolarization. • Phase space density in the nearEarth plasma sheet is comparable to phase space density at geosynchronous orbit. • Plasma Sheet: M 2800MeV / G f me3 j 1.661010 s 3 km6 2 2 pc 3 109 s 3 km6 • Geosynchronous Orbit: M 2100MeV / G f me3 3 109 108 s 3 km6 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.