1. Oxygen Injection Events observed by Freja Satellite
M. Yamauchi1, L. Eliasson1, R. Lundin1,
S. Arverius1, and O. Norberg2
Swedish Institute of Space Physics,S Kiruna, Sweden
2. Swedish Space Corporation - Esrange, S 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. O+ injection adjacent to cusp at lower energy than H+.
3. A multiple dispersion event of injecting heavy ions from a single localized spot of anisotropic energization within 1000 km distance from the spacecraft.

2. Importance of O+ circulation in space
ion escape H+ O+
< 10 eV (2~3 Re)
2~5
1~3
> 10 eV (3~4 Re)
2~8
1.5~20
* in Evolution of Earth, planets,
satellites
* in Modeling of ancient Earth
* in Atmospheric environment
* in Chemistry of reservoir
(CO2, SiO2, SO)
* in Basic plasma physics
* in Solar-terrestrial physics
(energy and mass transfer)
* in General plasma/neutral
circulation in the exosphere
ion precipitation
ion
electron
> 10 eV (DMSP)
0.2~0.9
9~60
in 1025 /s
mass budget H+ O+
meteors
out
0.05~0.2
0.5~5 - in
< 0.02
???
0.5
in kg/s
After Moore et al., 1999
Facts: # O+ escapes a lot (1~10 kg/s from Earth/Mars)
# O+ behaves differently from H+ (for return flow)
# But O+ return is not well studied
Prognoz-7 O+ H+ O+ H+ e- H+ O+
Cluster observation of oxygen escape from the Earth [Nilsson et al., 2004] H+
O+,O2+
O+ in the magnetosheath [Eklund et al., 1997] O+
Phobos-2: O+ escape from Mars [Lundin et al., 1990]. High escape rate : 0.1 ~ 1 kg/s (obs. by Mars Express and Phobos 2)
Freja: Escape of ions (mostly O+) due to wave-heatings (three types) [Norqvist et al., 1998].

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 ( keV) from Freja
* Obtain distribution/statistics & Examine exceptional cases
in 1° x 1h bin.
Clear nightside preference
Some in dayside
Not artifact of 63°inclination
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.

4. #1 + #2 : 1994-2-21 ~1330 UT event #2 O+ H+ e- event #1 cusp " SPI "
11 MLT MLT
13 MLT MLT O+ H+
energy ratio = 15~20
68°CGLat
66°CGLat
63°CGLat
Kp=7+ , IMF ≈ 50 nT (dawnward)
Freja energy-time spectrogram and geomagnetic activity.
1. Heavy ion (labeled O+ but could include N+): keV
2. Proton (H+): keV
3. Filed-aligned electron (e-): keV

5. #1. Midday Mon Heavy Ion Injection Event
Mono-energetic heavy ion injection (0.3-1 keV range) at L=7
The O+/H+ energy ratio = 15~20 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 UT to :32:06 UT (6 spin)
* Time-of-flight (TOF) distance ≈ 1 Re Þ unrealistic
* Velocity filter (VF) distance > 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
(C2) opposite hemisphere
= cusp (IMF BY effect)
Þ possible

6. #2. Heavy Ion Injection Adjacent to the Cusp
Only this event in > 100 cusps Þ different from FAST result
Lower energy than H+ Þ different from FAST result
Why Freja (h=1700km) - FAST (h= km) 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 O+ H+ e- O+ event #3 "wedge" radiation belt?
9 MLT MLT
(1)
(2)
(3) O+
P/A=40~140°
P/A=90~180°
P/A=0~90°
60°CGLat
63°CGLat
66°CGLat
Kp=6-
Freja energy-time spectrogram and geomagnetic activity.
1. Heavy ion (labeled O+ but could include N+): keV
2. Proton (H+): keV
3. Energetic electron (e-) keV
4. Field-aligned electron (e-): keV

8. #3. Multiple Heavy Ion Dispersion Event
Multiple heavy ion injection (0.1-3 keV) at 60°-65° at 9 MLT
Downgoing >> Upgoing Þ Injection (Not heating by wave)
Without H+ Þ Only heavy ions (O+ or N+)
Oblique rather than perpendicular Þ Source distribution
Non-gyrotropic Þ ? (ΩO+ ≥ 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) 18:50:10 UT (0.56 keV to 0.13 keV in 12s) Þ TOF=10s
(2) 18:50:25 UT (1.0 keV to 0.24 keV in 24s) Þ TOF=25s
(3) 18:50:40 UT (2.4 keV to 0.32 keV in 75s) Þ TOF=45s
Þ simultaneous start times (within 5 second)
* Time-of-flight (TOF) distance < 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 ΩO+ , i.e., <100km)
Þ Can be multiple sources & source distribution = 1 peak
In any interpretation, the generation mechanism is a mystery

9. Summary of Heavy Ion Injection Events
We examined all heavy ion data of Freja satellite ( )
* 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 > 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 < 1000 km.
Generation mechanism is a mistery