Solar Wind-Magnetosphere Interaction for
N th
Northward
d IInterplanetary
t
l
t
M
Magnetic
ti Field
Fi ld
Paul Song
Center for Atmospheric Research
Universityy of Massachusetts Lowell
• LLBL formation
• Global model
• Summary
Acknowledgments: C. T. Russell, T.I. Gombosi, D.L. DeZeeuw
Structure of the Magnetopause
Northward IMF
Southward IMF
Distribution Functions Across the Magnetopause
Summary of LLBL Observations
for Northward IMF
• Density and temperature change in steps:
against
i t diffusion
diff i tto b
be iimportant
t t
• 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
Southward
IMF
[D
[Dungey,
1961]
Northward
IMF
[Dungey, 1963]
Song and Russell Model [1992]
Reconnection
R
ti ttakes
k place
l
on th
the stagnant
t
t fi
field
ld li
line att regions
i
of high field shear
After Cusp Reconnection
• As Alfvenic kink propagates to lower latitudes, the newly
reconnected field line “sinks”
sinks into the magnetosphere
• Note the foot of the field moves sunward
NBZ Model
•
Entry Mechanism
o Th
Through
h
reconnection at two
hemispheres the
magnetosphere
captures
t
a
segment of a solar
wind flux tube
o The newly captured
flux tube sinks into
the magnetosphere
via propagating
Alfven waves.
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 ρ 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?
Global Modeling the Solar WingM
Magnetosphere-Ionosphere
t
h
I
h
System
S t
Challenges
• The topological status of the magnetosphere: open or
closed?
l
d?
• Driver(s) of ionospheric sunward flow
• Source(s) of NBZ currents
• Key problem: are “viscous cells” driven by viscosity?
Ionospheric Observations for
NBZ
Field-aligned current
[Ijima and Potemra, 1978]
Precipitation particles
[Newell and Meng, 1994]
Ionospheric Convection and Field
Perturbations for NBZ [Potemra et al.,
al 1984]
Ogino’s
Og
o s code, NBZ,, [Ogino
[Og o and
a d Walker,
a e , 1984]
98 ]
• Cusp
p reconnection
• Closed magnetosphere
Rice Model, NBZ [Usadi et al., 1993]
•
•
•
Cusp merging
Cl
Closed
d magnetosphere
h
Shorter tail for large IMF magnitude
Fedder and Lyon (1995), NBZ MHD Simulation
Noon-midnight
meridian
Equatorial
Plane
•
•
•
•
•
Cusp merging
Closed magnetosphere
4 ll ionosphere
4-cell
i
h
convection
ti
NBZ currents
Flow diversion at 95 Re
Raeder’s
aede s Model,
ode , NBZ [Raeder
[ aede et al.,
a , 1995]
995]
• Cusp
p
reconnection
• Tail
reconnection
ti
• Open tail
• No ionospheric
convection is
shown
Ogino’s code, NBZ, [Bargatze et al., 1999]
•
Cusp reconnection
•
Closed magnetosphere
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
Raeder’s
aede s Model,
ode , NBZ [Raeder
[ aede et al.,
a , 1995]
995]
• Cusp
p
reconnection
• Tail
reconnection
ti
• Open tail
• No ionospheric
convection is
shown
Global Picture
•
Solar wind and magnetosphere are
coupled through high latitude
reconnection.
•
For due NBZ, the magnetosphere
p the cusps
p
is closed except
Three topological boundaries and
regions.
Outer magnetosphere: two
convection channels and two cells
cells.
•
•
–
–
–
•
LLBL is driven by pressure
gradients.
“Viscous” cells are driven at
ionosphere by Pedersen currents
currents.
A region of stagnant flow near
midnight in the tail between 20-50
Re depending on the IMF strength:
cold-density
y plasma
p
sheet.
Ionosphere:
–
–
–
4-cell convection.
NBZ, Region I, and (Region II currents,
not modeled).
)
Polar caps, although closed, see
solar wind particles
NBZ MHD Simulation (Michigan Code)
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
S
l wind
i d entry:
t reconnection.
ti
LLBL flow: driven by pressure force.
Magnetotail length: increases with 1/BIMF, NSW, MSW.
Reverse cells: driven by reconnection and LLBL
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)
g
p
) origin
g ((mistaken by
y some p
people
p as evidence of an open
p region).
g )
•
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 anticorrelation between the number of sentences with the significance of work)