IONOSPHERIC OUTFLOW
AND ITS RELATIONSHIP TO
Ionosphere-ThermosphereMagnetosphere Coupling
W.K. Peterson
Laboratory for Atmospheric and Space Physics
University of Colorado, Boulder
Thanks to: Bob Strangeway, Andrew Yau, Chris
Cully,
Laila Andersson, Takumi Abe, John
IUGG2003, GAII.01, June 30, 2003
Foster
Topics
• Plasma outflow is a minor player in the energetics of
coupling between the ITM region and the Magnetosphere
• Ion outflow does not follow directly from Joule heating.
- There are a significant lag time and additional high altitude
process required before outflow can
begin.is not outflow
• Upflow
• Thermal O+ permeates the magnetosphere even in times
of low
- Energetic O+ can appear in the magnetosphere rapidly in response
activity.
to geophysical
events.
- The
plasmasphere
is
important
for
He
and
O
storage and release
+
+
• We are just beginning to obtain reliable information on
what conditions in the topside ionosphere are associated
with ion
outflow.
M/I-T Coupling
•The strongest and most important component of M/I-T coupling
is
through large scale field-aligned currents.
•The plasma outflow response is energetically weaker
•We are interested in plasma outflow because we expect that
outflow from the I-T could be an important feedback mechanism
acting in the magnetosphere
Ion outflow does not follow directly from Joule
- There are a significant lag time and additional high altitude
heating.
energization required before outflow can
begin.
Exobase =>
300 km
and
many
meanpaths
free
below
=>
Most of what goes up doesn't go out
Velocity required to reach the plasma sheet ~ 10 km/s
( < 1 eV H+ -- 2 eV He + -- 10 eV O + -- 20eV NO +)
Typical velocity in topside ionosphere << 1 km/s (up and down!)
Extreme (Kp =9) velocity in topside ionosphere < 3
km/s
Lockwood and
Titheridge
GRL,
1981 et al. JGR 1991
Loranc
Inferred upward
flux radars is
from
typically orders of
magnitude less than
the actual escaping flux
Escape velocity is acquired above 1000 km
through a variety of processes
•Upflowing
thermal
plasma moderate
acquires
energies in the
polar cap and
plasmasphere.
•Thermal plasma
is significantly
energized on
auroral and cusp
field
lines.
O
+
He
+
0
H
+
10
Abe, JGR, 1993
20
+
0
H
+
15
km/s
6000-9000 km
Kp ≤ 2+
3- ≤ Kp≤4+
Kp ≥ 5-
Yamada,
200
1
•Day-night asymmetry in velocity.
•Auroral and cleft O+ contribution.
+
Thermal Ion Outflow: Akebono SMS
Observations
O
He
900
0
500
0
100
0
-10
Velocity
(km/s)
•Polar-wind-like flow characteristics.
•Temporal-spatial variations associated
with local ionospheric conditions.
Altitude
<1
eV
1
8
50
°
6
2.5-5 eV
Inferred Ionospheric Source of O+ ions
Observed on Akebono
1
2
0
1-2.5 eV
>5
eV
Ionospheric source location of thermal-energy (<1 to >5 eV) O+ ions observed on Akebono
Energization on auroral
field lines is structured
mostly in latitude
From Dynamics Explorer 1
Transverse
energization of ions
(i.e. the formation of
ion conics) occurs
over extended altitude
regions on auroral
field lines.
The "conic" angle folds
up
more slowly at higher altitudes
than expected from the
… adiabatic invariant
contour
s
Σ Kp
F
7
10.
UFI
Flux
Seasonal Variation:
Winter/summer
ratio
He+: ~ 2.5
O+ : > 1
nightside
<1 dayside
H+ ~ 1
Solar-cycle
Variation:
Solar-max/solar-min
ratio:
H+ : ≤
1+:>
O
1
UFI flux distribution above 6000 km altitude observed on POLAR TIMAS
from Winter 1996 to Winter 1998 (Peterson et al., JGR, 2001)
O+
H+
H+
O+
O+
Ref. Yau et al., 1988
Ds
t
Kp
Energetic Upflowing Ion Outflow Rates: DE1/EICS
H+
A
O+
NOTE: The Flow is NOT
E ZERO at minimum activity
H+
F
10.
Kp 0 ∅ 6: 20-fold7 O+ and 4-fold H+ increase;
Solar min ∅ max: 10-fold O+/ H+ increase;
Thermal O permeates the
+
magnetosphere even in times of low
activity.
•Significant, measurable, fluxes of O+, H+ and He+
acquire escape velocity even during intervals of
low geomagnetic activity.
•O+ in the magnetosphere doesn't have to come
directly from the ionosphere in response to
geophysical events.
•The plasmasphere is important for He+ and O+
storage and release
+
+
+
Plasmaspheric storage and
release of H , He and O
Some, not all, of the
intensehave
events
detectable in the top
signatures
side
ionospher
e
Observation of Plasmaspheric
He+ leaking from the
magnetosphere into the
cusp/magnetosheath from
Polar
. R/RE ~ 5
MLT
11:30
H+ down flowing < 500
eV
He+ mode not compatible with this display
O+ < 500 eV
Upflowing
He+ drifting across field lines
into the cusp/magnetosheath
This is a rare event. It's
the only one I've found in
the Polar/TIMAS data set.
Effects of Low-energy Ion Outflow
in the Central Plasma
Sheet
Simulated fluxes of ionospheric H+ and O+ ions
FROM
Akebono
TO
the plasma sheet boundary
at low Kp (Cully et al. 2003b)
What determines magnitude and
location of ion ouflow
• We are just beginning to
systematically investigate
• Local Correlations
this.
- Strangeway, Su
• Global Correlations
- Cully/Yau, Moore
• Boundary Correlations
- Andersson/Peterson
Local Ion Flux vs Poynting Flux
From FAST
Strangewa
y
Yosemite
,
2003
.
Observations
Outflow Connections
F -Normalized net and upward fluence (i.e.
10.7
effects
of F removed) vs. solar wind
10.7
From Akebono
< 9000 km Cully et al.,
parameters
2003a
10.7
clock
clock
Stepwise multiple regression to
distinguish "independent"
between
and
"dependent"
correlations
"Independent"
(robust)
parameters:
- EUV flux F
- velocity latitude V
lat
- pressure p
- IMF variability σB
,φ
- KE flux Φ
KE
- IMF clock angle cosine cos (θ
V-B
"Dependent" (non-
cone
)
Global Thermal Fluence:
Dependence on Solar-Wind
Parameter
s
•
•
•
parameters:
robust
)
long
- Kp, Dst, B , n,
- σV, E2, V IMF
,φ ,θ
Correlations of outflow with
magnetospheric boundaries
•FAST data for
1997
•Polar cap boundary identified from electrons
•Equatorward boundary identified from ion loss cone
signatures
•Scale mass resolved H+/O+ upflowing fluxes observed
between boundaries into a constant latitude width
auroral zone and accumulate the data.
•Preliminary results presented here:
Oxygen
Flux-1
Invariant Latitude
Kp < 2
18 MLT
18 MLT
12
MLT
12
MLT
12
MLT
12
MLT
18 MLT
Altitude 1500-3100 km
Kp > 2
18 MLT
12
MLT
12
MLT
3100-3800 km
12
MLT
12
MLT
18 MLT
18 MLT
>3800
km
12
MLT
12
MLT
12
MLT
12
MLT
6 MLT
6 MLT
30
0
0
3x107
3x106
3x105
30
0
0
3x107
3x106
3x105
in each pixel
(s cm2)(s cm2)-1
Particle Flux
in each pixel
Number of events
1
Particle Flux
Number of events
The net total particle flux, where the downward loss cone flux is subtracted
Flux
Kp > 2
Kp < 2
18 MLT
18 MLT
12
MLT
12
MLT
12
MLT
12
MLT
18 MLT
Altitude 1500-3100 km
Oxygen
18 MLT
12
MLT
12
MLT
3100-3800 km
12
MLT
12
MLT
18 MLT
18 MLT
12
MLT
12
MLT
30
0
0
3x107
3x105
30
0
0
3x107
3x105
in each pixel
(s cm2)(s cm2)-1
Particle Flux
in each pixel
Number of events
1
Particle Flux
Number of events
>3800 km
12
MLT
12
MLT
6 MLT
6 MLT
The net total particle flux, where the downward loss cone flux is subtracted
Kp < 2
18 MLT
18 MLT
12
MLT
12
MLT
12
MLT
12
MLT
18 MLT
18 MLT
12
MLT
12
MLT
3100-3800 km
12
MLT
12
MLT
18 MLT
Altitude 1500-3100 km
Kp > 2
Preliminary
Oxygen Mean Energy (eV)
18 MLT
>3800
km
12
MLT
12
MLT
12
MLT
12
MLT
6 MLT
6 MLT
30
0
0
3x102
0
30
0
0
3x102
0
in each pixel
Anti-Earthward (eV)
Characteristic energy
in each pixel
Number of events
Anti-Earthward (eV)
Characteristic energy
Number of events
Conclusion
s
• Some of the thermal plasma that goes up
from the ionosphere gets energized and
makes it into the magnetosphere
• What? When? Where? Why? and How? are still
good questions to
ask.
• Thermal
O
permeates the
+
magnetosphere and doesn't have to come
directly from the ionosphere in response
to geomagnetic events
Backup slides follow
x
THERMAL ESCAPE. The classic example of an escape process for light gases is thermal or Jeans escape,
formulated in 1904 (13, 14). The basic idea is that, above some critical level now usually called the
"exobase," atoms in the high-velocity tail of the Maxwellian distribution must escape if they are
directed upward at or above the escape velocity, which is 11.2 km/s for Earth. The exobase level is
500 to 600 km for Earth. Thermal escape generally explains the observation that only the most
massive bodies in the solar system have dense atmospheres, and also that atmospheres are
generally deficient in light atoms such as H and He (except in the Jovian planets). It does suggest
that heavy gases, and possibly even N, should be stable on our moon, and at the beginning of this
century the lack of a substantial lunar atmosphere was a stumbling block to the acceptance of the
Jeans equation. Of course, the objection vanishes if the moon never had such an atmosphere. Other
loss processes probably dominate, at least currently.
The ionosphere/thermosphere is coupled to the magnetosphere by large scale field
aligned currents, ion outflow, and plasma waves. The temporal and spatial scales of
these processes and their coherence are not fully understood. Large scale field aligned
currents are closed deep in the region of the thermosphere/ionosphere where collisions
Between neutral particles dominate. The energy deposited by Joule heating is
transported slowly upward at thermal velocities. Ion outflow originates high in the
thermosphere/ionosphere in the transition region (i.e. exobase) where collisional and
transport processes are of comparable importance. In this region typical thermal
velocities are significantly below the ~10 km/s escape velocity determined by Earth's
gravity; nevertheless a significant flux of ions escapes into the magnetosphere. The
composition of ions escaping into the magnetosphere is completely different from the
composition of the exobase (transition region). Different mass dependent
mechanisms
provide the additional energy needed for ion escape in the polar wind, cleft ion
fountain and auroral acceleration region. Interpretations of satellite observations of
escaping ions made from satellites are further complicated by storage and episodic
release of significant quantities of He+ and O+ from the plasmasphere. Some
investigators have suggested that inhomogeneities in the mass density in the Earth's
magnetotail are triggers for magnetospheric substorms, which, in turn, result in
significant intensifications of Joule heating. In this paper we will review how the
observations of escaping ions have been used to unravel some of the parts of this
complex coupled system.
Ion Outflow Control - Summary
Dayside averages of particle and field fluxes show that ion
outflows are correlated with:
• DC Poynting flux
• Precipitating electron density
• Alfvén wave Poynting flux
ELF waves are also correlated, but their effects can be assumed
into other parameters.
Point by point correlations show that:
• Dayside: DC Poynting flux is better than electron density (!)
• Nightside: Electron precipitation is better
• Alfvén waves seem to show greater control as fluctuating
fields (RMS), than than net Poynting flux.
Ion Flux v Electron Density
Outflow Connections - 1