FG4. Plasma Entry and Transport into and within the Magnetotail

Report of PET sessions at GEM summer workshop, June 22-27, 2008.

Conveners: Antonius Otto <ao [at] how.gi.alaska.edu>, Jay R. Johnson <jrj [at] pppl.gov>, and Simon Wing <Simon.Wing [at] jhuapl.edu>

At this workshop, PET had two sessions: 1. southward IMF and 2. northward IMF. In addition, PET had a joint session with the MI coupling FG that focuses on ion outflow and its effects on the magnetotail transport and solar wind entry. The summaries of the northward and southward IMF sessions are given below while the summary of the joint session is to be given by the MI coupling FG.

PET : Southward IMF

a. Electric field mapping and convection

1. Larry Lyons reviewed the two main issues in mapping the convection pattern from the ionosphere to the magnetosphere: the potential and induced electric field. The potential electric field concerns with the particles crossing the field line whereas the induced electric field concerns with the changing magnetic field which has no significant effect in the ionosphere.

2. Jo Baker compared the results of mapping Cluster EDI electric field observations with T96 with SuperDARN convection pattern. He found that 24% of EDI measurements are not accounted for by SuperDARN, but generally there was good agreement. The convection patterns for duskward, dawnward, and northward IMF were considered.

3. Yukitoshi Nishimura examined a storm event with Themis in which the convection is weak in the plasma sheet, but strong in the flanks and inner magnetosphere. Only one out of five spacecraft observed steady convections. He found that the dawn-dusk electric field Ey = (VxB)y.

b. Plasma sheet driving of the inner magnetosphere

4. Matina Gkioulidou presented a simulation that examines the roles of plasma sheet cold ions. She found that enhanced cold ions near midnight increases shielding while enhanced cold ions in the flanks enhances fast flow near midnight.

5. Vahe Peroomian presented a simulation of a storm event where most particles only enter from the dawn flank and there was a path for cold ions to move from dawn magnetopause all the way to the inner magnetosphere. Simulation results show qualitatively similar features with HENA observations. In comparison, fewer particles enter from the deep tail, although this occurs in his simulations for different events.

c. Solar wind entry

6. John Lyon showed that KH waves are present in the flanks for both northward and southward IMF. The plasma sheet density increases with the solar wind speed. Curiously the plasma sheet refilled from the flanks rather than traditionally thought through lobe/mantle reconnection. The cold ions are transported toward the midnight meridian through the instability interchange. There is no dawn-dusk asymmetry.

d. Entropy

7. Gary Erickson showed that PV exhibits characteristic differences for substorms, convection bays, and pseudo breakups. In the latter PVreturns to earlier levels (Bubbles), but PV stays depressed in the substorm expansion for a few 10 minutes and in convection bays for hours.

e. Solar wind and magnetic activity influences

8. Yiqun Yu presented a storm main phase simulation (BATSRUS) that shows that solar wind Vx but not solar wind ram pressure, linearly drives with thermal pressure in the plasma sheet. At other The observed density and pressure agree with the simulation. IMF Vx has stronger influences than IMF Bz on dayside reconnections.

9. Chih-Ping Wang showed Geotail data that suggest that when AE is increasing the density peaks at the flanks, but when AE is decreasing, density decreases at all LT. The velocity shows a dawn-dusk asymmetry that is consistent with the dawn-dusk asymmetry.

PET : Northward IMF

a. Solar wind entry

1. Benoit Lavraud showed observations of plasma distributions with three different populations: two cold components and one hot component associated with Kelvin-Helmholtz modes at the flank boundary for northward IMF.

2. Chris Chaston showed wave spectra as evidence for kinetic Alfven waves at the dayside flank boundary. The wave were associated with parallel electron and perpendicular ion heating and the diffusion coefficient was estimated to 1010 m2/s.

3. Wenhui Li showed that MHD simulation for double cusp reconnection which leads to thick boundary layer on the dayside during northward IMF. The density and velocity agree with Themis observations, but the temperature and magnetic field do not agree as well. He discussed also that in the boundary layer, plasma flows southward for a summer dipole tilt.

4. Margaret Chen presented an analytical magnetosheath model that agrees with the Spreiter gasdynamic model. Particle tracing shows that more energetic ions, having larger gyro radii, can enter the magnetosphere more easily.

5. Antonius Otto presented analytical estimates of the relation of mass transport and entropy mixing for double reconnection and KHI. Differences in the plasma transport for cusp and three-dimensional KH were addressed.

6. Jay Johnson illustrated how perpendicular ion and parallel electron heating is consistent with kinetic Alfven dynamics as for instance observed by Chaston.

b. Transport of cold ions to the midnight meridian

7. Simon Wing shows that cold ion entropy increases by a factor of 5 going from the flanks to the midnight meridian, suggesting that as yet unidentified transport mechanism would heat the cold ion nonadiabatically.

c. Solar wind influences

8. Xinlin Li showed that solar wind speed highly correlates with the LANL energetic electron fluxes and that the correlation is better for southward IMF than northward IMF. Solar wind electrons do not correlate with these energetic electrons. Hence, it is not clear how and where these electrons are accelerated.

d. Outstanding questions

9. Jay summarized the outstanding questions

• What is the cause of dawn-dusk asymmetries observed at the magnetospheric flanks? How do they depend on solar wind velocity, IMF orientation (Parker spiral), mechanism (Cusp reconnection, Kelvin-Helmholtz, Kinetic Alfven waves)?
• How does plasma transport from the flanks to the center of the plasma sheet? What is the role of convection verses turbulence?
• How do kinetic-Alfven waves couple with velocity driven (KH) waves and how does it affect transport?
• What are the mechanisms, fluxes, energies, and spatial distributions of ionospheric material in the magnetotail and their impact on the transport into and within the tail?