Hot He + events in the inner magnetosphere observed by Cluster 1 Yamauchi, et al. (2014), JGR, doi: /2013JA Inner magnetosphere: Majority of ions are drifting by magnetic and electric drifts M. Yamauchi

Inner magnetospheric ions (2013 result) 2 Species? Ion + of keV (CODIF instrument) Target? He + enhancement that is independent of H + and O + Period? (~300 relatively clean data / ~760 traversals)

Note on inbound-outbound asymmetry * Cluster orbit is North-South symmetric during * Quickest scan of all latitude near perigee (due to high apogee) ⇒ energy-latitude patter is expected to be inbound- outbound symmetric, but reality is more asymmetric:

Cluster Statistics Decay in time partly came from rapid degradation of the sensor

(a) Vertical stripes: Nearly no dispersion over keV. Only found near midnight during substorms, and mostly inbound- outbound asymmetric (life time~1h) ⇒ substorm injection. (b) Wedge-like energy-latitude dispersed sub-keV ions. Often found in the morning to noon sectors some hours after a substorm. ⇒ drift ions of <0.1 keV source. (c) Local bursts of low-energy ions: a peak energy flux less than 100 eV but not thermal. Found all local time without clear relation to geomagnetic activities (life time~1h). ⇒ a local phenomena? (d) Warm trapped ions confined near equator: tens eV to a few hundred eV without dispersion. Found all local time without clear relation to geomagnetic activities (life time~1h). ⇒ a local wave particle interaction (wave mode is not yet identified) Knowledge by 2013

Why Mass? Magnetic drift (Energy dependent) * gradient-B drift * curvature drift ⇒ dominant for > 10 keV ExB drift (Energy independent) * co-roration E-field * external E-field ⇒ dominant for < 0.1 keV Both types of drift predict the same energy-time-pitch angle distribution for different mass if initial energy/location is the same, but reality is:

Sometimes Mass dependent! * Sometime heated He + are observed in the inner magnetosphere at different energies from H+ or O+ (ion cyclotron wave is the strongest candidates (e.g., Young et al., 1982). p/a < 45° p/a ≈ 90° 7

(a) Vertical stripes 8 Appearances of H +, He +, and O + are not always correlated

Timing & energy are quite different among H +, He +, and O + (drift theory predicts same energy-time diagram for all species). (b) Wedge-like energy-latitude dispersed ions

(b-1)10 (1) Strong (but similar between H + & He + ) energy- latitude dispersion ⇒ long drift time under moderate geomagnetic disturbance). (2) mainly in ⊥ direction to the geomagnetic field (trapped) (3) Time scale~1 h? (too little statistics of multiple spacecraft observations) (4) Timing (or energy) of He + is quite different from that of H + (or O + ). ⇒ Different source location between H +, He +, and O +.

(b-2) 11 Similar to (b-1) but (1) H + intensity is much less than He + intensity or O + intensity. (2) After long quiet periods.

(c-1) Local burst12 (1) Only He + (faint H +, no O + or He ++ ) in ⊥ (trapped) direction to the geomagnetic field. (2) No energy-time dispersion (= no drift) for He +, while very faint H + with energy-latitude dispersion. (3) During or right after substorms mainly in the late evening sector. (4) Time scale~1 h? (too little statistics of multiple spacecraft observations) (5) Within outer plasmasphere

Similar to A but (1) Pitch angles of He + and H + are completely different and (2) During quiet condition npEynpEy detached plasmasphere 13 (c-2) Local burst

date (SC4)UTMLTIlatRTypeprevious ALAL value : local-A350 nT : local-A?600 nT : local-A-500 nT : local-A?250 nT : local-A300 nT : local-A-700 nT :2617±635local-A?600 nT : local-B< : local-Bbaselinebaseline=11h nT : remote-A : remote-Abaselinebaseline=6h : remote-A200 nT : remote-A-400 nT :5423±624remote-B :1723±59~614.0~4.1remote-B :1416±604remote-B100 nT (>3h)200 nT : remote-B/A? : remote-B :46 0±60~614.4remote-B All clear events All are located at outer plasmasphere

Where: Inner Magnetosphere at L=4~7 (Cluster perigee) Species: He + of 0.05~5 keV (CIS/CODIF energy range) Target: He + enhancement (type a-c) independent of H + and O + Data: (~300 relatively clean data out of ~760 traversals) Distribution 15

(d) Warm trapped ions confined near equator Sometime show E(H + ) < E(He + ) while majority is E(H + ) = E(He + ). ⇒ Heated e.g. by He cyclotron waves (1980’s) 16

equator Equatorially-confined hot ions sometime show E(H + ) < E(He + ) while majority is E(H + ) = E(He + ). He+ is certainly heated e.g. by He cyclotron waves (1980’s) Example of local heating 17

Summary Low-energy (< keV) He+ enhancement events without the same type H + enhancement in the inner magnetosphere (L=4-7) are surveyed using all Cluster perigee traversals during For categories (b) drifted one & (c) local burst, ~20 clear (& ~10 unclear) events are found in about 300 traversals. All events are found in the outer plasmasphere. For both categories, various distributions (pitch angles, energy, and mass ratio) that are classified (here two examples are shown). Locally heated ones in the evening sector are related to substorm activities and remote types in the noon are found after long quiet period. 18

Conclusions For (b) wedge-like dispersion, He + was somewhat filtered from H + and O +, and one possibility is different start location between H +, He + and O + after escaping from the ionosphere. During (c) Local heating, the plasmasphere is sometimes energized in a mass dependent way in the evening sector during substorms. The selective He + energization might take place during quiet periods near noon. ⇒ We need more investigation on Mass dependency 19

Future study 20 Nitrogen Ion TRacing Observatory (NITRO) for next ESA's M-class call North In-situ (spinning) Cold ion mass spectrometer Hot ion (3~4 different types) Energetic ions Photoelectron Magnetometer+Waves (Ω N ) Langmuir Probe (plus alpha) UV/visible (narrow FOV) IR (narrow FOV) Cold ion mass spectrometer Hot ion mass analyser Photolectron Magnetometer Langmuir Probe (plus alpha) South FOV Imaging (3-axis) & monitoring Daughter (gradient)