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Cusp Radiation Source: A Challenge for Theory and SimulationJiasheng Chen, Theodore A. Fritz, Katherine E. Whitaker,Forrest S. Mozer, and Robert B. SheldonIn 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
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 Bywould move the dayside northern cusp into pre-noon (e.g., Cowley et al., JGR, 96, 5557, 1991).
Cusp Diamagnetic Cavities (CDC): |B| with turbulence. Cusp energetic Particle (CEP) CDC at 9:30 MLT (pre-noon)
CDC at 14-23 UT on 5/13/99 with a size of ~ 6 Re. Cusp
Solar wind conditions for the 5/13/99 CDC Since By < 0, a CDC at pre-noon was expected. By < 0
Other CDC observations under different solar wind conditions: • Normal solar wind speed, vsw = 450 km/s • Fast solar wind stream, vsw = 900 km/s • Slow solar wind flow, vsw = 380 km/s (two examples presented)
Pre-noon Post-noon (Fritz et al., JGR, 108, A1, 1028, 2003)
By>0, <Dst>=1.6 nT, CDC at pre-noon; unexpected By>0 CDC at 10:30 MLT
Cusp energetic He++ Cusp energetic O+
By>0, <Dst>=5.5 nT, CDC at pre-noon;unexpected By>0 CDC at 10:20 MLT
3b. Slow solar wind flow, vsw=380 km/s 19 UT 15 UT 15 UT 19 UT
By>0, <Dst>=-82 nT, CDC at 8:30 MLT;unexpected ISEE-3 10/30/78 IMF By>0 CDC ISEE-1
Energetic Charged Particles in CDC CEP electron CEP proton CDC
CEP and Fields • CEP flux increase • with E-field increase • and B-field Decrease. • 2. Emax = 50 mV/m
Blow up cusp E-field near peak fluctuation Showing some polarization Waves at different Frequencies.
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 By >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.