Oxygen Injection Events observed by Freja Satellite M. Yamauchi1, L. Eliasson1, R. Lundin1, S. Arverius1, 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. 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.

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].

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 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.

#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 = 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+): 0.01-10 keV 2. Proton (H+): 0.01-10 keV 3. Filed-aligned electron (e-): 0.03-20 keV

#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 keV@13:31:30 UT to 0.18 keV@ 13:32:06 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

#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=2000-4000km) 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

#3 : 1992-12-28 ~1850 UT O+ H+ e- O+ event #3 "wedge" radiation belt? 9 MLT 10 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+): 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

#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

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 > 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