The Magnetospheric Cusp:
Solar Wind – Magnetosphere –
Ionosphere – Thermosphere
Coupling
R. J. Strangeway
IGPP & ESS /UCLA
Special Acknowledgement to J. Raeder, UNH, and the
Community Coordinated Modeling Center.
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
1
Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
2
What is so Special About the Cusp?
• The cusp is the region that provides the most direct path from the
solar wind to the ionosphere and thermosphere
• The cusp requires an understanding of several processes:

Reconnection topology and Interplanetary Magnetic Field direction
effects (IMF By)

Steady-state, multi-point, and time-varying reconnection

Particle kinematics (time-of-flight, velocity dispersion)

Field-aligned current generation

Joule Dissipation – ion and neutral upwelling and outflows
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
3
Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
4
Anti-parallel merging [Luhmann, 1984]
B = (0,0,1)
(northward)
B = (0,1,0)
(By only)
B = (0,0,-1)
(southward)
B = (0,-1,-1)
Luhmann et al. [1984] used Spreiter
gas dynamic model to map IMF to
the magnetopause
Contours show regions of
anti-parallel merging (up to 90˚)
Crooker [1985] used superposition of
IMF and Chapman-Ferraro field at
magnetopause, considered
component merging
Cooling [2001] extended Luhmann et
al. [1984] to allow for component
merging
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
5
Cooling Model – Component Merging
Luhmann et al. [1984]
June 19, 2012
Cooling et al. [2001]
GEM - Cusp Tutorial - R. J. Strangeway
6
Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
7
Trattner et al. [2012] component and
anti-parallel merging
Characteristic signature of cusp is
energy dispersed ions
Plot shows Polar data at ~ 5.5 Re
Mapping to magnetopause
(source region) uses time-of-flight
energy dispersion comparing
downgoing to reflected [Onsager
et al., 1990]
vhdispersion
T = Rr + 2R
Multiple
events
could
m
be because
v T =of:
R
•
•
•
June 19, 2012
r
Multiplel reconnection
sites
Time-varying reconnection
Rr = 2R
vh - vl
High latitude
andmlow-latitude
reconnection (different history)
GEM - Cusp Tutorial - R. J. Strangeway
(
)
8
Trattner et al. [2012], different topology
By-dominated –
nearly anti-parallel,
multiple X-lines?
June 19, 2012
Southward Bz –
anti-parallel,
multiple injections
from same point
GEM - Cusp Tutorial - R. J. Strangeway
Northward Bz –
component
merging, extended
region
9
IMF By – Hemispherical Asymmetry
Østgaard et al. [2005]
investigate cusp proton
precipitation asymmetry
using IMAGE (viewing
north) and Polar (viewing
south)
Cusp precipitation
consistent with locus of
anti-parallel merging
Bx contributes to hemispherical differences
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
10
Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
11
Newell et al. [2007] – Forward Dispersion
“FAST”
DMSP
Note: At low altitudes the spacecraft moves through structures
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
12
Newell et al. [2007] – Reverse Dispersion
“FAST”
DMSP
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
13
Newell et al. [2007] – Double Cusp
“FAST”
DMSP
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
14
Double Cusp – Wing et al. [2001]
Wing et al. [2001] argue that
double cusps are because the
dispersing ions come from
two different reconnection
sites
DMSP data from Newell et al.
[2007] (not the same event)
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
15
Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
16
Force Balance
For simplicity assume
neutrals at rest (frame
of reference)
Ionospheric flow:
Frozen-in electrons:
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
17
IMF By-Dependent Convection
Currents
Convection
By > 0
By < 0
Burch et al. [1985]
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
18
Weimer [2001] FAC morphology
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
19
FAST Orbit 8276 – Strong IMF By
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
20
MHD FAC Predictions
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
21
Field Topology – Shock Passage
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
22
FAST Orbit 8284 – Double Cusp?
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
23
Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
24
Ion Outflows
Type 1
Type 2
Type 1 and Type 2 defined by Wahlund et al. [1992]
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
25
Ion Outflows – Including Alfvén Waves
Type 1
Type 2
Type 1 and Type 2 defined by Wahlund et al. [1992]
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
26
Joule Dissipation and Heating Rates
Plasma frame:
Neutral frame:
Rate of
temperature
increase:
dTnF nmi dTi F n ni dTi F
=
=
dt nn mn dt n in dt
Minority species temperature increases more rapidly
See [Strangeway, JGR, 2012]
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
27
Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
28
Cusp Statistics – Knipp et al. [2011]
Poynting flux statistics from DMSP
Southern hemisphere is mirrorreflected about noon as a function
of IMF By
Events required |By| > 10 nT
(a) N:By < 0, Bz < 0; (b) N:By > 0, Bz < 0
(c) N:By < 0, Bz > 0; (d) N:By > 0, Bz > 0
Red is 100 µW/m2
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
29
Thermospheric Response –
Crowley et al. [2011]
CHAMP sees strongly
neutral density modulation
near the cusp
Modified TIME-GCM using
real-time AMIE data
shows enhanced densities
too
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
30
Poynting Flux Versus Neutral Density –
Crowley et al. [2011]
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
31
Small scale FACs – Lühr et al. [2004]
CHAMP also sees large-amplitude
small-scale FACs in the Cusp
Lühr et al [2004] argue that these can
significantly enhance the heating
Heating rate depends on E2,
But there is an issue with time scales,
neutrals heat much more slowly than
ions
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
32
Summary
• Reconnection topology controls the location of the cusp
• There is both a high latitude (anti-parallel merging) and low latitude
(component merging) source of dispersing ions – depends on IMF
orientation
• Field-aligned currents and Joule dissipation in the ionosphere strongly
affected by IMF By – I suggest this is high latitude merging
• Ion outflows and neutral upwelling both appear to be associated with
Joule dissipation – question of timescales for the neutrals
June 19, 2012
GEM - Cusp Tutorial - R. J. Strangeway
33