1. 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?

2. Reiff and Burch (1985), NBZ with By

3. Kan and Burke (1985) NBZ with Bx
Open
Closed

4. Burch et al. (1992) NBZ model (with By)

5. Crooker (1992), NBZ with Dipole Tilt
Superposition of dipole and IMF
Static model (V=0)
Lobe cells: open-to-open reconnection
Merging cells: closed-to-open/open-to-closed reconnection

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

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

8. 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

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

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

11. Superposition Of Magnetic Field Model/Method [Siscoe]
B=BIMF + Bdipole
Separatrix surfaces are found, separating regions of different topologies.
Two null points are identified. Field lines on the separatrix surfaces converge to or diverge from these two points.
Separator lines are founded, that connect the two nulls.

12. Watanabe et al., [2005]; NBZ with Dipole Tilt
Two possible sequences
In each case, reconnection takes place at different times in the two hemispheres

13. Watanabe et al. [2005]; NBZ with Dipole Tilt
Just inside northern open-closed boundary, field lines converge to a single point in the other hemisphere
This is impossible if the field lines are moving

14. Watanabe et al. [2005]; NBZ with Dipole Tilt
Just inside southern open-closed boundary, field lines converge to a single point in the other hemisphere
Can this be possible?

15. Watanabe et al. [2005]; NBZ with Dipole Tilt
Field-aligned flows from the ionosphere
The inner boundary condition (Dirichlet) does not allow field-aligned flow

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

17. Reconnection Takes Place on Stagnant Field Line

18. Structure of the Magnetopause
Northward IMF
Southward IMF

19. NBZ Model
Through reconnection at two hemispheres the magnetosphere captures a solar wind flux tube
The captured flux tube assimilates to the magnetosphere through Alfven wave propagation

20. After Cusp Reconnection
As Alfvenic kink propagates to lower latitudes, the newly reconnected field line “sinks” into the magnetosphere

21. 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)
The only way to expand is along the magnetopause to the flank

22. Global Picture
For due NBZ, the magnetosphere is closed except the cusps
The solar wind particles flow along the LLBL and in the tail
The polar caps, although closed, see solar wind particles
The outer magnetosphere is driven through ionosphere powered by the Pedersen currents

23. Ionospheric Coupling

24. NBZ MHD Simulation (Michigan Code)

25. Conclusions
With better and better computer simulation models, the knowledge of modeling becomes more and more important in order to safeguard the simulation model and to understand and interpret correctly the simulation results.
Modeling links observation, knowledge, and predictions for remote regions in space with physical laws.
It provides top level qualitative physical understanding of a problem or a simulation result.
There are principles in how to perform modeling, but few people apply them to constraining their models or interpretations.
It is time for more people to know the principles and guidelines of modeling.