Oxygen Injection Events observed by Freja M. Yamauchi IRF-Kiruna * Motivation / Examples * Distribution (mainly in nightside) * Unusual events (dayside)

Phobos-2 (ASPERA) observation of two type of oxygen escape

We know that oxygen is escaping with much higher rate than thermal escape model predicts ==> However, oxygen budget between Earth and space has barely been studied despite its obvious importance on: * evolution of Earth, planets, satellites * modelling ancient Earth (astrobiology issue) * environmental issue * energy and mass transfer from the solar wind * plasma and molecular circulation, etc. Why does Earth have so much Oxygen while Mars have so little?

Oxygen Budget/Circulation: O+ supply from oxides (e.g., CO 2 and SiO 2 ). * Oxygen escape / energization mechanism: Thermal (Jean) escape vs Non-thermal escape (night & cusp) * Role of the escaped oxygen in space: e.g., Mass-loading effect by escaped ions. * Oxygen circulation in the inner magnetosphere: If oxygen does not return, Earth should have lost its atmosphere. Simplest assumption = geomagnetic field push it back * Oxygen precipitation into the ionosphere: Very few works ==> this is today's topic

Commonly-found ion injections near or equatorward of the nightside auroral zone. (a) With heavy ions dominant.

Commonly-found ion injections near or equatorward of the nightside auroral zone. (b) With proton dominant.

Analyses is simple and straight forward Look at all the data and * Check the distribution and statitistics * Further study on the exceptional cases But no work was published during past 15 years except 1 cusp paper. I don’t understand why.

Distribution of heavy ion injections in 1° x 1h bin. Total number of traversals with clear injection events at each bin is scaled by the size of the square. The number with # is the orbit number.

Distribution of heavy ion injection events at keV range. * Nightside preference * Some exceptions in dayside This is not the artifact of Freja orbit with inclination of 63°because most injections are found inside CPS, a region far equatorward from the polar cap boundary.

Unusual event #1 and #2: Kp=7+, IMF ≈ 50 nT.

AE and ASY indices (12-hour plot) before the event #1 and #2: The thick vertical line indicates the Freja observation of the injection event.

#1. Midday Heavy Ion Injection Event * during extremely high magnetospheric activity * strong dawnward IMF => cusp (≈ substantial magnetic noon) is shifted toward dawn * Mono-energetic heavy ion injection (0.3-1 keV range) is observed at 13 MLT (13:31:30 UT). * Eenergy band (width in %) of injecting ions is about the same for proton and heavy ions ==> only one species despite during mgnetic storm. * The energy ratio between the injecting heavy ion and proton species is constant at about ==> O+ rather than N+ or C+ if originate from the same region. * This is not the stagnant plasma injection (SPI) event which is recognized at 13:28:25-13:29:20 UT in the proton channel.

Two possible interpretations for monotonic energy-time dispersion

(a) TOF case : ∆T = H TOF / V //2 - H TOF / V //1 or H TOF = ∆T * V //2 * V //1 / ∆V // note : pitch-angle dependence

(b) simple VF case L 1,2 / V C = H VF / V //1,2,L 2 - L 1 = ∆T * V sat therefore H VF / V //2 - H VF / V //1 = ∆T * V sat / V C or H VF = H TOF * V sat / V C L 1,2 = H TOF * V sat / V //1,2

Downgoing ions of ≈ 300 eV (60 km/s for O+) at L=7 : 0.32 UT & :32:06 UT (6 spin) ==> * Time-of-flight (TOF) distance ≈ 1 Re Unrealistic * Velocity filter (VF) distance > 10 Re Location: ==> equitorial/opposite hemisphere

Peculiarity * Dayside location ==> Where do they come from? * Heavy ions are registered first (at higher latitude) before protons are registered (at lower latitude). ==> What is the mass-filtering mechanism? * Only O+ but not N+ despite storm condition ==> What causes N+ escape at all? * Only this event during entire Freja mission ==> What is the peculiarity of this period?

Possible sources and transport routes for the dayside heavy ions:

Discussion on event #1 (1) Peculiarity of this period? Unusually strong dawnward IMF (≈ 50nT) Major storm (but many other periods as well) (2) Source location * nightside ==> difficult * dayside same hemishpere ==> difficult * opposite hemosphere = cusp! ==> possible (note: northern/southern cusp = prenoon/postnoon) (3) Source mechanism? * Non.thermal escape from the cusp (but why selective to O+?) (4) Mass-filtering mechansim? ????

#2. Heavy Ion Injection Adjacent to the Cusp * during extremely high magnetospheric activity * Another heavy ion injection is observed adjacent to the cusp (13:27:20 UT). * Among more than 100 cusps observed by Freja, this is the only one with heavy ion injection at different energy from H+ * the oxygen energy is lower than the proton energy (both at 13:27:30 UT) contrary to the common cases observed by FAST (McFadden et al., 2003). ==> We cannot identify the source mechanism and the source region for this specific case: * drifted ions from the nightside? * escaping ionospheric ions reflected at high-altitude cusp? * escaping ions from the opposite hemisphere? * ???

Freja (h=1700km) - FAST (h= km) discrepancy: Only FAST detected O+ during magnetic storms ==> possible explanations are: * Downgoing O+ in the cusp is higher than the upper energy threshold of Freja (e.g., ring current origin)? * Loss process (e.g., mirror reflection and charge-exchange) right above Freja is more important for O+ than for H+? * Thermalization right above Freja is so strong that Freja can register H+/O+ in a wide energy range to overlap each other? * Strong O+ injection occurs only for special magnetic storms. At present we have no answer to the FAST-Freja discrepancy. ==> To solve this problem, we need another low-altitude satellite (< 2000 km) with a 3-D mass-resolving ion spectrometer with high energy and pitch-angle resolutions.

Unusual event #3: Kp = 6-. The third panel is energetic ( keV) ions

#3. Multiple Heavy Ion Dispersion Event * Two outstanding features in the heavy ion channel: (1) wedge-like dispersed structure of trapped oxygen at around 18:47 UT (52-58 CGLat) (2) the overlapping and diverging energy-time dispersions at 18:50: :52:30 UT (61-65 CGLat). * They are injections (downgoing count >> upgoing count) * No H+ signature = exclusively a heavy ion (O+ or N+) event. * They are multiple injections with different dispersion strength. 18:50:10 UT (0.56 keV => 0.13 keV in 12s) => TOF=10s 18:50:25 UT (1.0 keV => 0.24 keV in 24s) => TOF=25s 18:50:40 UT (2.4 keV => 0.32 keV in 75s) => TOF=45s ==> Simultaneous start times (18:49:55-18:50:00 UT) * TOF distance < 1000 km * No similar observation during entire Freja mission.

Same event: blow-up of 3 different sectors’ heavy ion data: ±45° pitch-angle, upward direction, and downward direction.

AE and ASY indices (12-hour plot) before the event #3 : The thick vertical line indicates the Freja observation of the injection event.

* Rather in the oblique direction than in the downgoing direction * Detected during one of two half-spin periods (non-gyrotropic). note: O+ gyro frequency at 1700km ~ hundred Hz ==> Phase-mixing when travelling > 1s ==> Yet not gyrotropic ==> Are they really injection events or heating by wave? ==> But interpreting then as wave signature is even harder. Non-gyrotropic distribution + downgoing flux suggests very anisotropic source (beam-like) and: (1) perpendicular convection is extremely large (~ 100 km/s), ==> very unlikely(no signature of fast convection) (2) Anisotropy of the source distribution was maintained ~ 1min. ==> single source with three directions of beams ==> Injection must has large perpendicular component. (3) Very close source (several tens gyro period <1s, i.e., <100km) ==> multiple source

Short source distance (<1000km) makes it difficult to be detected by other spacecrafts (e.g. Viking and FAST), and the ground. Victoria (closest station from the foot-point of Freja during event ) does not show any specific intensification.

Summary of heavy ion injection events * Surveyed entire Freja data ( ) * Nightside preference * Some unusual event in dayside (1) O+ injection at 13 MLT followed by H+ injections. VF source > 10 Re (TOF distance ~ 1 Re). From the southern dayside ionosphere Mass-filtering mechanism is unknown. (2) O+ injection (lower energy than H+) adjacent to the cusp Freja-FAST discrepancy (3) Overlapping heavy ion injection with diverging dispersion In oblique non-gyrotropic directions Sudden localized anisotropic energization at < 1000 km. Generation mechanism is completely unknown.