Dynamic Motion of Bow Shock and Magnetopause Observed
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)
Magnetopause Bow shock ? 13. 5 2
Magnetopause Bow shock 3
Normal directions of boundaries UT boundary Normal direction (GSE) Method 05: 50 Magnetopause (0. 980, -0. 103, -0. 169) MVA 07: 52 Magnetopause (0. 996, -0. 080, -0. 044) MVA 07: 54 Magnetopause (0. 985, -0. 077, -0. 153) MVA 07: 59 Bow shock (0. 813, -0. 292, -0. 504) Coplanarity 08: 01 Bow shock (0. 292, -0. 550, 0. 782)* Coplanarity 11: 06 Bow shock (0. 956, -0. 142, 0. 256) Coplanarity Shock normal from coplanarity method: n=(Bux. Bd)x(Bu-Bd)/|(Bux. Bd)x(Bu-Bd)| *question: why the shock normal at 08: 01 is different from others? 4
Magnetopause Discontinuity Timing analysis shows: Both the magnetopause and the discontinuity move anti-sunward but at different speed. Magnetopause: ~30 km/s; discontinuity: ~ 90 km/s. 5
Discontinuity Magnetopause Vx ~ 90 km/s Vx ~ 30 km/s 6
Where are the energetic ions (~10 ke. V) from? • Magetospheric population peaks at ~ 6 ke. V, and this peak is not present in the magnetosheath from 0755 to 0757, suggesting these ions are not from magnetosphere. 7
• Not from the sun
Shock acceleration? WIND data Quasi-Para Shock Quasi-Perp Shock 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 ~1106 UT) Time difference is 2 hours! However… 9
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 (~10 ke. V) 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.
- Slides: 10