1. MULTI-INSTRUMENT STUDY OF THE ENERGY STEP STRUCTURES OF O + AND H + IONS IN THE CUSP AND POLAR CAP REGIONS Yulia V. Bogdanova, Berndt Klecker and CIS TEAM Collaboration with: Edita Georgescu (FGM team) Matt Taylor, Ian Krauklis, Andrew Fazakerley (PEACE team) Harri Laakso (EFW team) Nicole Cornilleau-Wehrlin (STAFF team) Patrick Canu (WHISPER team)

2. Energy step structures of O + and H + ions in the cusp and polar cap, May 18 2001, CIS data overview Energy-time spectrograms for H + and O + from the S/C 1, 3 and 4 for May 18, 2001, 02:00-04:00 UT: The H + population shows the typical cusp distribution with energy dispersion. The magnetopause crossing is marked by dashed blue lines. In the oxygen spectrograms we can see a O + beam with the following features: the oxygen beam population ‘tracks’ the upper edge of the H+ population in the energy flux spectrogram, has a very narrow energy range, and shows energy dispersion from 1-2 keV in the cusp region to 20- 40 eV in the polar cap. Simultaneous energy step structures in the H+ and O+ populations.

3. Energy step structures of O+ and H+ ions in the cusp and polar cap, Solar wind and IMF data Data from ACE: interplanetary magnetic filed, velocity and density of solar wind. The dashed line shows the beginning of the time period of interest for us, about 1 hour before the Cluster observations. During this time there were very unstable interplanetary conditions: the Bz-component of the IMF varies from negative to positive values five times.

4. Energy step structures of O + and H + ions in the cusp and polar cap, Orbit configuration and AE index The left figure presents the satellite orbit during 18 May 02:00-04:00 UT. The S/C moved through the northern polar cap and cusp regions from the nightside to the dayside in the X-direction and away from the Earth in the Y- and Z-directions. The right figure shows the AE-index for 18 May. During 02:00-04:00 UT there was high geomagnetic activity with a few subsequent substorms, the Kp-index was 3-.

5. Energy step structures of O + and H + ions in the cusp and polar cap, S/C configuration The figure shows the precise relative configuration of S/C 1, 3 and 4 at 03:00 UT in GSE coordinates. In all coordinates the satellites moved in the following sequence: S/C 1 first, S/C 4 second, S/C 3 third. The dominant velocity is in the – Y direction. Note, that during this event the separation distance was rather high, 1-3 Re

6. Energy step structures of O + and H + ions in the cusp and polar cap, O + 3D-moments comparison from S/C 1, 3 and 4

7. Energy step structures of O + and H + ions in the cusp and polar cap, O + distribution functions, S/C 1 At 02:25:20 O + distribution function shows beam-like behavior, at 02:35:40 distribution function shows high perpendicular heating.

8. Energy step structures of O + and H + ions in the cusp and polar cap, O + distribution functions, S/C 1 At 02:42:22 O + distribution function shows beam-like behavior, at 02:45:27 distribution function shows perpendicular heating.

9. Energy step structures of O + and H + ions in the cusp and polar cap, O + distribution functions, S/C 1 At 02:53:06 O + distribution function shows beam-like behavior, at 02:56:15 distribution function shows high perpendicular heating

10. Energy step structures of O + and H + ions in the cusp and polar cap, O + distribution functions, S/C 1 At 02:57:03 O + distribution function shows high perpendicular heating, at 02:45:27 distribution function shows beam-like behavior.

11. Energy step structures of O + and H + ions in the cusp and polar cap, H + pitch-angle spectrogram, low energies, S/C 1 The H + maximum energy flux is at pitch-angle=90 o, this corresponds to high perpendicular heating.

12. Energy step structures of O + and H + ions in the cusp and polar cap, H + pitch-angle spectrogram, middle energies, S/C 1 The H + maximum energy flux is at pitch-angle=90 o, this corresponds to high perpendicular heating.

13. Energy step structures of O + and H + ions in the cusp and polar cap, H + pitch-angle spectrogram, high energies, S/C 1 The H + maximum energy flux is at pitch-angle=90 o, this corresponds to high perpendicular heating.

14. Energy step structures of O + and H + ions in the cusp and polar cap, 3D-distribution of the H + differential flux at 02:44:47 UT

15. Energy step structures of O + and H + ions in the cusp and polar cap, 3D-distribution of the H + differential flux at 02:57:03 UT

16. 16 Energy step structures of O + and H + ions in the cusp and polar cap, 3D-distribution of the H + differential flux at 03:11:56 UT

17. Energy step structures of O + and H + ions in the cusp and polar cap, S/C 1, CIS and FGM data In FGM data – probably manifestation of F-A currents?

18. Energy step structures of O + and H + ions in the cusp and polar cap, S/C 1, PEACE, EFW and STAFF data During times of energy steps there are enhancements of wave spectral density in a broad frequency range and electron density.

19. Energy step structures of O + and H + ions in the cusp and polar cap, S/C 4, CIS and FGM data In FGM data - probably manifestation of F-A currents.

20. Energy step structures of O + and H + ions in the cusp and polar cap, S/C 4, PEACE, EFW, STAFF and WHISPER data During times of energy steps there are enhancements of wave spectral density in a broad frequency range and electron density.

21. Energy step structures of O + and H + ions in the cusp and polar cap, S/C 3, CIS and FGM data

22. Energy step structures of O + and H + ions in the cusp and polar cap, S/C 3, EFW and STAFF data During times of energy steps there are enhancements of wave spectral density in a broad frequency range.

23. Energy step structures of O + and H + ions in the cusp and polar cap, Ions transverse heating mechanisms The heating can be associated with broadband extra low frequency (BBELF) wave fields,waves near the lower hybrid (LH) frequency, or electromagnetic ion cyclotron (EMIC) waves near 0.5 f H+. The heating can also be correlated with auroral electrons, suprathermal electron burst (STEBs), or precipitating H + ions. Furthermore, types 1 and 2 are often associated with field- aligned currents.

24. Energy step structures of O + and H + ions in the cusp and polar cap, Times of O + energy steps at different S/C 1 st energy step in O+ population is observed: S/C 1 – 02:35 UT S/C 4 – 02:41 UT S/C 3 - 02:49 UT. The separation distance between S/C in X- direction: S/C 1 – S/C 4 = 0,45 Re S/C 4 – S/C 3 = 0,65 Re S/C 1 – S/C 3 = 1,1 Re From partial moments: plasma tailward convection velocity: Vx = -11,5 km/s t conv S/C 1 - S/C 4 = 4,2 minutes t conv S/C 4 - S/C 3 = 6 minutes t conv S/C 1 – S/C 3 = 10,1 minutes  t S/C 1 - S/C 4 = 6 minutes  t S/C 4 - S/C 3 = 8 minutes  t S/C 1 – S/C 3 = 14 minutes Plasma convection times between S/C are compatible with the time delays of the energy step observation at different S/C. Probably, we observe the same energy step structure at different S/C with time delay around plasma convection time.

25. Energy step structures of O + and H + ions in the cusp and polar cap, Summary We present a study of one cusp crossing event during 18 May 2001, 02:00-04:00 UT. The observation was made during a time with rather high geomagnetic activity and conditions favorable for reconnection at the magnetopause. The O + beam population tracks the upper edge of the H + population in the energy-time spectrogram. It has a very narrow energy range, and shows energy dispersion from 1-2 keV in the cusp region to 20-40 eV in the polar cap. The O + observation can be explained by a localized source of accelerated ionospheric ions with velocity V, determined by the superposition of outward particle motion V II with tailward convection V  x. V  x as determined at S/C 1 and 4 are very similar in the polar cap region, indicating similar convection on the spatial scale of S/C separation, i.e. 1,1 Re. Energy step structures are observed simultaneously in O + ionospheric population and H + mixed mirrored magnetosheath and ionospheric populations. A comparison of the time delays between energy step structures of O + population at the different S/C with the plasma convection time between S/C shows, that we observe the same structure at all three S/C with a time delay compatible with the convection time. Our study shows that energy steps in the O + and H + populations are associated with high transverse heating of both species. Ion energy steps are observed simultaneously with electron density enhancements measured by the PEACE instrument and enhancements of wave activity in a broad frequency range of 0,3- 4000 Hz detected by EFW, STAFF and WHISPER instruments. We conclude that observed ion energy step structures are very likely caused by resonant energization by broadband extra low frequency wave fields.