1. Cusp Radiation Source: A Challenge for Theory and Simulation Jiasheng Chen, Theodore A. Fritz, Katherine E. Whitaker, Forrest S. Mozer, and Robert B. Sheldon In cooperation with: J. F. Fennell, M. Klida, K. Kudela, V. N. Lutsenko, J. Niehof, J. S. Pickett, J. Roeder, C. T. Russell, G. L. Siscoe, W. N. Spjeldvik, and K. Trattner

2. Theory and simulation predict: Cusp is a precipitation region for particles; A positive IMF By would move the dayside northern cusp into post-noon; A negative IMF By would move the dayside northern cusp into pre-noon (e.g., Cowley et al., JGR, 96, 5557, 1991).

3. Cusp Diamagnetic Cavities (CDC): |B| CDC at 9:30 MLT (pre-noon) with turbulence. Cusp energetic Particle (CEP)

4. Cusp CDC at 14-23 UT on 5/13/99 with a size of ~ 6 Re.

5. Solar wind conditions for the 5/13/99 CDC Since B y < 0, a CDC at pre-noon was expected. B y < 0

6. Other CDC observations under different solar wind conditions: 1. Normal solar wind speed, v sw = 450 km/s 2. Fast solar wind stream, v sw = 900 km/s 3. Slow solar wind flow, v sw = 380 km/s (two examples presented)

7. 1. Normal solar wind speed, v sw =450 km/s 4/22/99

8. (Fritz et al., JGR, 108, A1, 1028, 2003) Pre-noon Post-noon

9. B y >0, =1.6 nT, CDC at pre-noon; unexpected B y >0 CDC at 10:30 MLT

10. 2. Fast solar wind stream, v sw =900 km/s 6/28/99

11. Cusp energetic He++ Cusp energetic O+

12. B y >0, =14.7 nT, CDC at 7MLT; unexpected CDC + +

13. 3a. Slow solar wind flow, v sw =380 km/s 4/25/99

14. POLAR, 4/25/99

15. B y >0, =5.5 nT, CDC at pre-noon; unexpected B y >0 CDC at 10:20 MLT

16. 3b. Slow solar wind flow, v sw =380 km/s 15 UT 19 UT 15 UT 19 UT

17. B y >0, =-82 nT, CDC at 8:30 MLT; unexpected B y >0 CDC 10/30/78 ISEE-1 ISEE-3 IMF

18. Energetic Charged Particles in CDC CEP electron CEP proton CDC

20. CEP Energy Spectrum

21. CEP vs. Outer Radiation Belt Particles Proton phase space density

22. He++ & O+ phase space densities:  Cusp Radiation Source

23. CEP and Fields 1.CEP flux increase with E-field increase and B-field Decrease. 2. Emax = 50 mV/m

24. Blow up cusp E-field near peak fluctuation Showing some polarization Waves at different Frequencies.

25. Left-hand polarization

26. Left-hand polarization

28. Summary CDC is a large radiation region, and CEP is a new radiation source. Under different solar wind and geomagnetic conditions, CDCs have been observed at pre-noon in the northern hemisphere when IMF B y >0 (duskward). These observations are unexpected by the existing models and MHD simulations and provide a new challenge for the current theory and simulations. Cusp ions can be energized by both resonant and stochastic acceleration mechanisms.