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. 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 Oxygen is important AND O+ escapes a lot (1~10 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 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. event #2 #1 + #2 : 1994-2-21 ~1330 UT 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

5. Mono-energetic heavy ion injection (0.3-1 keV range) at L=7 The O+/H+ energy ratio = 15~20Þ O+ (0.3 keV= 60km/s) Narrow bandÞ only O+ , not N+ despite storm condition O+ before H+Þ ??? (mass filtering mechanism) Only this event in 2.5 yearsÞ due to strong IMF BY (≈ 50nT)? #1. Midday Mon Heavy Ion Injection Event 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 ReÞunrealistic * Velocity filter (VF) distance > 10 ReÞpossible ∆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

6. Only this event in > 100 cuspsÞ 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 #2. Heavy Ion Injection Adjacent to the Cusp

7. event #3 O+ H+ e- e- #3 : 1992-12-28 ~1850 UT "wedge" radiation belt? 9 MLT 10 MLT (1) (2) (3) O+ O+ 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

8. Multiple heavy ion injection (0.1-3 keV) at 60°-65° at 9 MLT Downgoing >> UpgoingÞ Injection (Not heating by wave) Without H+Þ Only heavy ions (O+ or N+) Oblique rather than perpendicularÞ Source distribution Non-gyrotropicÞ ? (ΩO+ ≥ 100 Hz ~ phase-mixing within 1s) note: no signature of strong (~ 100 km/s) convection. Only this event in 2.5 yearsÞ ? #3. Multiple Heavy Ion Dispersion Event 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 Þsimultaneous 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. 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). ÞFrom 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 Summary of Heavy Ion Injection Events