1. Solar Wind-Magnetosphere Interaction for Northward Interplanetary Magnetic Field
Paul Song
Center for Atmospheric Research
University of Massachusetts Lowell
LLBL formation
Global model
Summary
Acknowledgments: C. T. Russell, T.I. Gombosi, D.L. DeZeeuw

2. Structure of the Magnetopause
Northward IMF
Southward IMF

3. Distribution Functions Across the Magnetopause

4. Summary of LLBL Observations for Northward IMF
Density and temperature change in steps: against diffusion to be important
Indication of mixtures of plasmas of magnetosphere and magnetosheath origins at different ratios
Thicker and faster on the nightside
Smaller density gradient and velocity shear on the nightside

5. Northward IMF [Dungey, 1963]
Southward IMF [Dungey, 1961]
Northward IMF [Dungey, 1963]

6. Song and Russell Model [1992]
Reconnection takes place on the stagnant field line at regions of high field shear

7. After Cusp Reconnection
As Alfvenic kink propagates to lower latitudes, the newly reconnected field line “sinks” into the magnetosphere
Note the foot of the field moves sunward

8. NBZ Model Entry Mechanism
Through reconnection at two hemispheres the magnetosphere captures a segment of a solar wind flux tube
The newly captured flux tube sinks into the magnetosphere via propagating Alfven waves.

9. Formation of the LLBL
After the captured flux tube becomes a magnetospheric flux tube
The original flux tube is compressed and shortened (magnetic volume decreases =>B and  increases)
Total pressure of the flux tube increases.
The flux tube expands (increase in length or volume) along the magnetopause to the flank via interchange instability
Ionospheric dissipation drags the motion
Successive reconnection events form multiple layers of LLBL
Interpenetration and mixing of plasmas of two origins result in decreased ratio of magnetosheath-to-magnetosphere population: an aging process
How can the flux tube flow back?

10. Global Modeling the Solar Wing-Magnetosphere-Ionosphere System
Challenges
The topological status of the magnetosphere: open or closed?
Driver(s) of ionospheric sunward flow
Source(s) of NBZ currents
Key problem: are “viscous cells” driven by viscosity?

11. Ionospheric Observations for NBZ
Field-aligned current Precipitation particles
[Ijima and Potemra, 1978] [Newell and Meng, 1994]

12. Ionospheric Convection and Field Perturbations for NBZ [Potemra et al

13. Ogino’s code, NBZ, [Ogino and Walker, 1984]
Cusp reconnection
Closed magnetosphere

14. Rice Model, NBZ [Usadi et al., 1993]
Cusp merging
Closed magnetosphere
Shorter tail for large IMF magnitude

15. Fedder and Lyon (1995), NBZ MHD Simulation
Noon-midnight meridian
Equatorial Plane
Cusp merging
Closed magnetosphere
4-cell ionosphere convection
NBZ currents
Flow diversion at 95 Re

16. Raeder’s Model, NBZ [Raeder et al., 1995]
Cusp reconnection
Tail reconnection
Open tail
No ionospheric convection is shown

17. Ogino’s code, NBZ, [Bargatze et al., 1999]
Cusp reconnection
Closed magnetosphere

18. Global MHD Simulation For Northward IMF
Reconnection Tail Tail-length Ionosphere
Ogino-Walker cusp closed ~1/B
Wu cusp closed ~ 1/B
Usadi et al. cusp closed ~ 1/B
Fedder-Lyon cusp closed ~1/B 4-cell/NBZ
Raeder cusp+tail open
Michigan cusp closed ~ 1/B 4-cell/NBZ
Bargatze cusp closed ~ 1/B 4-cell/NBZ
ISM cusp closed 4-cell/NBZ

19. Raeder’s Model, NBZ [Raeder et al., 1995]
Cusp reconnection
Tail reconnection
Open tail
No ionospheric convection is shown

20. Global Picture
Solar wind and magnetosphere are coupled through high latitude reconnection.
For due NBZ, the magnetosphere is closed except the cusps
Three topological boundaries and regions.
Outer magnetosphere: two convection channels and two cells.
LLBL is driven by pressure gradients.
“Viscous” cells are driven at ionosphere by Pedersen currents.
A region of stagnant flow near midnight in the tail between Re depending on the IMF strength: cold-density plasma sheet.
Ionosphere:
4-cell convection.
NBZ, Region I, and (Region II currents, not modeled).
Polar caps, although closed, see solar wind particles

21. NBZ MHD Simulation (Michigan Code)

22. Summary
Chris and I first proposed a model of formation of LLBL for northward IMF
We then collaborated with Michigan group and developed a self-consistent global model for northward IMF:
Solar wind entry: reconnection.
LLBL flow: driven by pressure force.
Magnetotail length: increases with 1/BIMF, NSW, MSW.
Reverse cells: driven by reconnection and LLBL.
“Viscous cells”: driven at ionosphere by Pedersen currents.
Magnetopause definition: the magnetopause currents may differ from the topological boundary.
Stagnation line/point dilemma: No stagnation region in the magnetosheath. A stagnation line occurs in the magnetospheric field.
Ionosphere: Precipitation within (outside) the polar cap is of solar wind (magnetospheric) origin (mistaken by some people as evidence of an open region).
The most important things I learned from Chris:
A positive view toward referees and referee’s reports
There are “only” 3 ways to prove truth! (simulation is NOT among them!)
Can you summarize your thesis in one sentence, or two sentences, or … (an anti- correlation between the number of sentences with the significance of work)