1. 1 Dynamic Motion of Bow Shock and Magnetopause Observed by THEMIS Hui Zhang (BU) Q.-G. Zong (Umass Lowell) D. G. Sibeck (GSFC) T. A. Fritz (BU)

2. 2 Magnetopause Bow shock ? 13.5

3. 3 Magnetopause Bow shock

4. 4 Normal directions of boundaries UTboundaryNormal direction (GSE) Method 05:50Magnetopause(0.980,-0.103,-0.169)MVA 07:52Magnetopause(0.996,-0. 080,-0.044)MVA 07:54Magnetopause(0.985,-0. 077,-0.153)MVA 07:59Bow shock(0.813,-0. 292,-0.504)Coplanarity 08:01Bow shock(0.292,-0. 550,-0.782)*Coplanarity 11:06Bow shock(0.956, -0.142, 0.256)Coplanarity Shock normal from coplanarity method: n=(B u xB d )x(B u -B d )/|(B u xB d )x(B u -B d )| *question: why the shock normal at 08:01 is different from others?

5. 5 Magnetopause Discontinuity Timing analysis shows: Both the magnetopause and the discontinuity move anti-sunward but at different speed. Magnetopause: ~30 km/s; discontinuity: ~ 90km/s.

6. 6 Vx ~ 90 km/s Vx ~ 30 km/s Discontinuity Magnetopause

7. 7 Magetospheric population peaks at ~ 6 keV, and this peak is not present in the magnetosheath from 0755 to 0757, suggesting these ions are not from magnetosphere. Where are the energetic ions (~10 keV) from?

8. 8 Not from the sun

9. 9 Theta Bn: Angle between the IMF direction and the shock normal where Shock normal is (0.956, -0.142, 0.256)GSE (from THEMIS B observation at ~1106UT) Time difference is 2 hours! However… Shock acceleration? Quasi-Para Shock Quasi-Perp Shock WIND data

10. 10 Summary The magnetopause was found moving anti-sunward at ~30 km/s. Two subregions have been observed by all 5 THEMIS spacecraft in the magnetosheath associated with a discontinuity. This discontinuity traveled from the bow shock to the magnetopause at Vx ~ 90 km/s. Both low and higher energy ions are observed in the first region and only low energy ions are observed in the other subregion. What caused the shock, magnetopause moving anti-sunward? Where are the energetic ions (~10keV) from? –Not from the solar wind –May not from the magnetosphere –Quasi-Parallel shock acceleration? Has problem to correlate the IMF with the discontinuity marked by red arrows on slide 5.