Oxygen Injection Events observed by Freja Satellite

1
Oxygen Injection Events observed by Freja
Satellite

• M. Yamauchi1, L. Eliasson1, H. Nilsson1,
• R. Lundin1, and O. Norberg2
• Swedish Institute of Space Physics,S-98128
  Kiruna, Sweden
• 2. Swedish Space Corporation - Esrange, S-98128
  Kiruna, Sweden

We surveyed heavy ion injections at 1700 km
altitude. They are mostly found in nightside
subauroral region Only few are found in
dayside They seem to have different generation
mechanisms. Þ We show three of them during
magnetic storm.
(1) Mono-energetic O injection near local noon
with O first and H later. (2) Heavy ion
injection adjacent to cusp at lower energy than
H. (3) A multiple heavy ion dispersion event
which can be traced back to one localized
energization of dense oxygen with strong
pitch-angle anisotropy within 1000 km distance
from the spacecraft.
2
Oxygen is important
Space-level circulation of oxygen/heavy ions has
an obvious cross-disciplinary importance on
subjects such as Evolution of Earth,
planets, satellites Modeling of ancient
Earth (astrobiology) Atmospheric
environment Chemistry of reservoir (CO2,
SiO2, SO) Basic plasma physics
Solar-terrestrial physics / energy and mass
transfer Plasma and neutral circulation in
the exosphere
AND O escapes a lot (110 kg/s from
Earth/Mars) AND O behaves differently from H
O H e-
H O
H
Cluster observation of oxygen escape from the
Earth Nilsson et al., 2004
O,O2
O
Phobos-2 observation of oxygen escape from Mars
Lundin et al., 1990. Top energy-time
spectrogram. Bottom energy-mass matrix
3
Freja observation / general ion injections in
night/morning sectors
O not well-studied
O H e-
Freja examples
O H e-
H well-studied
Commonly-found ion injections near or equatorward
of the nightside auroral zone.
Search all heavy ion injection events (0.1-10
keV) from Freja Obtain distribution/statistics
Examine exceptional cases
in 1 x 1h bin.
Clear nightside preference Some in dayside Not
artifact of 63inclination
The total number of traversals with clear
injection events in each bin is scaled by the
size of the square. The numbers with are the
orbit number.
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1 2 1994-2-21 1330 UT
event 2
O H e-
event 1
cusp
" SPI "
11 MLT 12 MLT
13 MLT 14 MLT
O H
energy ratio 1520
68CGLat
66CGLat
63CGLat
Kp7 , IMF 50 nT (dawnward)
Freja energy-time spectrogram and geomagnetic
activity. 1. Heavy ion (labeled O but could
include N) 0.01-10 keV 2. Proton (H) 0.01-10
keV 3. Filed-aligned electron (e-) 0.03-20 keV
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1. Midday Mon Heavy Ion Injection Event
Mono-energetic heavy ion injection (0.3-1 keV
range) at L7 The O/H energy ratio 1520 Þ
O (0.3 keV 60km/s) Narrow band Þ only O , not
N despite storm condition O before H Þ ???
(mass filtering mechanism) Only this event in 2.5
years Þ due to strong IMF BY ( 50nT)?
Source Distance? 0.32 keV_at_133130 UT to 0.18
keV_at_ 133206 UT (6 spin) Time-of-flight
(TOF) distance 1 Re Þ unrealistic
Velocity filter (VF) distance gt 10 Re Þ
possible
?T HTOF / V//2 - HTOF / V//1 note
pitch-angle dependent
Time-of-Flight (TOF)
Velocity Filter (VF)
HVF / V//2 - HVF / V//1 ?T Vsat / VC or HVF
HTOF Vsat / VC
Source? Route?
(A) morning or (B) evening Þ difficult (C1)
dayside same hemisphere Þ difficult (C2)
opposite hemisphere cusp (IMF BY effect) Þ
possible
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2. Heavy Ion Injection Adjacent to the Cusp
Only this event in gt 100 cusps Þ different from
FAST result Lower energy than H Þ different
from FAST result Why Freja (h1700km) - FAST
(h2000-4000km) discrepancy? Upper energy
threshold of Freja is too low Þ probably no
O (not H) loss process right above Freja Þ
surprising Thermalization right above Freja
contamination Þ surprising Only during
special magnetic storms Þ need investigation
7
3 1992-12-28 1850 UT
event 3
O H e- e-
"wedge"
radiation belt?
9 MLT 10 MLT
(1)
(2)
(3)
O O O
P/A40140
P/A90180
P/A090
60CGLat
66CGLat
63CGLat
Kp6-
Freja energy-time spectrogram and geomagnetic
activity. 1. Heavy ion (labeled O but could
include N) 0.01-10 keV 2. Proton (H) 0.01-10
keV 3. Energetic electron (e-) 10-100 keV 4.
Field-aligned electron (e-) 0.03-20 keV
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3. Multiple Heavy Ion Dispersion Event
Multiple heavy ion injection (0.1-3 keV) at
60-65 at 9 MLT Downgoing gtgt Upgoing Þ
Injection (Not heating by wave) Without H Þ
Only heavy ions (O or N) Oblique rather than
perpendicular Þ Source distribution Non-gyrotropi
c Þ ? (?O 100 Hz phase-mixing within
1s) note no signature of strong ( 100 km/s)
convection. Only this event in 2.5 years Þ ?
If they are really injection events... They
have different dispersion curves (1) 185010
UT (0.56 keV to 0.13 keV in 12s) Þ TOF10s (2)
185025 UT (1.0 keV to 0.24 keV in 24s) Þ
TOF25s (3) 185040 UT (2.4 keV to 0.32 keV in
75s) Þ TOF45s Þ simultaneous start times
(within 5 second) Time-of-flight (TOF) distance
lt 1000 km Non-gyrotropic distribution
downgoing flux Þ Anisotropic source
distribution (1) Anisotropy of the source
distribution was maintained 1min. Þ Single
source source distribution 3 peaks (2)
Very close source ( 10 ?O , i.e., lt100km) Þ
Can be multiple sources source distribution
1 peak In any interpretation, the generation
mechanism is a mystery
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Summary of Heavy Ion Injection Events
We examined all heavy ion data of Freja satellite
(1992.10-1994.10) Most injection events occur
in the nightside Some unusual events in the
dayside (1) Mono-energetic injection with O
faster than H (13 LT) VF source gt 10 Re (TOF
distance 1 Re). Þ From the southern dayside
ionosphere (cusp) Mass-filtering mechanism is
unknown (2) O injection (lower energy than H)
adjacent to the cusp Freja-FAST
discrepancy Generation mechanism is
unknown (3) Multiple dispersive O injections
from a nearby source In oblique direction with
non-gyrotropic distribution Sudden localized
anisotropic energization at lt 1000
km. Generation mechanism is a mistery