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

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).

Cusp Diamagnetic Cavities (CDC): |B|

CDC at 9:30 MLT

(pre-noon)

with turbulence.

Cusp energetic Particle (CEP)

Cusp

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

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:

1. Normal solar wind speed, vsw = 450 km/s

2. Fast solar wind stream, vsw = 900 km/s

3. Slow solar wind flow, vsw = 380 km/s (two examples presented)

1. Normal solar wind speed, vsw=450 km/s

4/22/99

(Fritz et al., JGR, 108, A1, 1028, 2003)

Pre-noon

Post-noon

By>0, <Dst>=1.6 nT, CDC at pre-noon; unexpected

By>0

CDC at10:30 MLT

2. Fast solar wind stream, vsw=900 km/s

6/28/99

Cusp energetic He++

Cusp energetic O+

By>0, <Dst>=14.7 nT, CDC at 7MLT; unexpected

CDC

+ +

3a. Slow solar wind flow, vsw=380 km/s4/25/99

POLAR,4/25/99

By>0, <Dst>=5.5 nT, CDC at pre-noon; unexpected

By>0

CDC at10:20 MLT

3b. Slow solar wind flow, vsw=380 km/s

15 UT

19 UT

15 UT

19 UT

By>0, <Dst>=-82 nT, CDC at 8:30 MLT; unexpected

By>0

CDC

10/30/78

ISEE-1

ISEE-3

IMF

Energetic Charged Particles in CDC

CEP electron

CEP proton

CDC

CEP Energy Spectrum

CEP vs. Outer Radiation Belt ParticlesProton phase space density

He++ & O+ phase space densities: Cusp Radiation Source

CEP and Fields

1. 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 polarizationWaves at different Frequencies.

Left-hand polarization

Left-hand polarization

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.