1. Response of the Magnetosphere and Ionosphere to Solar Wind Dynamic Pressure Pulse KYUNG SUN PARK 1, TATSUKI OGINO 2, and DAE-YOUNG LEE 3 1 School of Space Research, Kyung Hee University, Korea 2 Solar-Terrestrial Environment Laboratory, Nagoya University, Japan 3 Dept. Astronomy and Space Science, Chungbuk National University, Korea 2009 UN BSS & IHY Workshop, September 21-25, 2009

2. Introduction The interaction of the solar wind with Earth’s magnetosphere produces various phenomena, such as substorms and aurora, in the polar region. When the IMF turns southward, the energy of the solar wind is efficiently trapped by reconnection in the magnetosphere, and convection and currents within in the magnetosphere increase. The orientation of the IMF has significant effects on convection pattern and the FAC system in the magnetosphere. [Fairfied and Cahill, 1966; Reiff and Bursh, 1985: Cowley and Lockwood, 1992]. Pure Southward Pure Northw ard By T. Ogino θ Y Z

3. Tilt angle 0° Tilt angle 30° Effect of the dipole tilt angle When the northern hemisphere is summer, the dayside reconnection occurred slightly below the magnetic equator in the start from 30 degree. Dayside Reconnection rate : 30  tilt ~ 0.84 times 0  tilt Configuration of the magnetic field lines

4. Southward IMF (315°) + dipole tilt (30°) Northward IMF (45°) + dipole tilt (30°) Configuration of the magnetic field lines [Park et al. 2006, 2009] # A quasi-steady state configuration usually resulted after about 3 hours in real time. X Z X Y 1. Dusk sector (northern hemisphere) 2. Move to dawn in the dayside 3. Come back to dusk in the tail 4. Tail reconnection successively occurs in the slant and elevated plasma sheet. Effect of the dipole tilt and IMF condition

5. Bz By Bz By Northward IMF (45°) + dipole tilt (30°) Southward IMF (315°) + dipole tilt (30°) Electric field |E| and Resistivity electric field 0.1 times E ηJηJ J || J┴J┴ EηJηJ J┴J┴ E APN (1.2)  E APS (1.1) ≥ E ME (0.2) ≥ E SS (0.1 mV/m) E APN, E APS (0.4) ≥ E ME, E SS (0.15 mV/m) The parallel component of the current (J || ) in the southern hemisphere is larger than northern hemisphere when the dipole tilt is positive. The feature is different result from the southward IMF condition [Park et al., 2006, 2009].

6. Northward IMF (45°) + dipole tilt (30°) In a view form the dusk In a view form the top In a view form the Sun

7. Northward IMF (45°) + dipole tilt (30°) Southward IMF (315°) + dipole tilt (30°) The reason of different J || in the reconnection region between the southward and northward IMF condition

8. Orientation of IMF and dipole tilt (30  ) Electric field |E| (E = -V  B+  J) E APN > E APS The electric field in the northern hemisphere is almost 3 times larger than that in the southern hemisphere for 45   .

9.  Polar cap potential saturation process and dayside magnetic reconnection enhancement [Boudouridis et. al., 2004]  Polar cap (PC) index enhancement [Lukianova, 2003]  Sawtooth oscillations in energetic particle flux and magnetic field at geosynchronous orbit [Lee et. al., 2004]  Auroral-region disturbance [Lyons et al., 2005]  Substorm triggering The effect of sudden enhancements of solar wind dynamic pressure on the magnetosphere and ionosphere Simulation Method  The number of grid points (n x, n y, n z ) = (300, 100, 100) with a grid spacing of 0.3 R E.  Solar wind parameters: IMF |B| = 0 nT, 2 nT and 10 nT Solar wind density ： n sw = 5/cc and 10/cc Solar wind velocity ： V sw = 300 km/s

10. Simulation condition Condition 1 : constant Bz and variable dynamic pressure Condition 4 : Bz south to northward 60 min t 5 10 [/cm -3 ] Bz = -2 nT and -10 nT density -2 -10 Density = 5 and 10 /cm -3 Bz [nT] 60 min t Condition 2 : more southward Bz and constant dynamic pressure Condition 3 : Bz change with dynamic pressure 60 min t 5 10 [/cm -3 ] density Bz = -2 nT Bz = -10 nT 60 min t 5 10 [/cm -3 ] density Bz = 0nT Bz = -10 nT

11. t pulse -5m t pulse +5m t pulse +10m t pulse +15m t pulse +20m Bz = -2 nT Nsw = 5/cc Bz = -2 nT Nsw = 10/cc Red (dawn to dusk ) Blue (dusk to dawn) Time evolution of the electric field in XY plane Simulation Results Bz = -10 nT Nsw = 5/cc Bz = -10 nT Nsw = 10/cc 30 20 -60 X 0 -20 Y 0 (R E ) a)a large viscous cell near the magnetopause but very little convection in tail b) large convection in tail Condition 1

12. t pulse -5m t pulse +5m t pulse +10m t pulse +15m t pulse +20m Time evolution of perpendicular current density Bz = -2 nT Nsw = 5/cc Bz = -2 nT Nsw = 10/cc Bz = -10 nT Nsw = 5/cc Bz = -10 nT Nsw = 10/cc X=-15R E large viscous cell Cross section in tail

13. t pulse -5m t pulse +5m t pulse +10m t pulse +15m t pulse +20m Time evolution of plasma pressure Bz = -2 nT Nsw = 5/cc Bz = -2 nT Nsw = 10/cc Bz = -10 nT Nsw = 5/cc Bz = -10 nT Nsw = 10/cc Location of Bowshock : 15.4 -> 14R E Location of Dayside Magnetopause : 11.5R E -> 10R E Location of Bowshock : 14.8R E ->13R E Location of Dayside Magnetopause : 11R E -> 9R E X (R E ) Y (R E ) 20 -20 30 -60

14. Bz = -10 nT, Nsw = 5/cc Bz = -10 nT, Nsw = 10/cc Bz = -2 nT, Nsw = 5/cc Bz = -2 nT, Nsw = 10/cc Vx > 0 tailward Vx < 0 earthward Tail reconnection 14~15 R E Tail reconnection ~11 R E Earthward flow has ~50 km/s, while the tailward flows ~150km/s (20 min) Earthward flow has ~300 km/s, while the tailward flows ~400km/s (10min) little change J  (  J~4) increases J  ~ 3times J  (  P~28) (  P~100)

15. Bz = -10 nT Nsw = 10/cc Bz = -2 nT Nsw = 5/cc Condition 3 t pulse -5m t pulse +5m t pulse +10m t pulse +15m t pulse +20m Time evolution of the electric field and plasma pressure in XY plane Compress by dynamic pressure Small convection in tail Location of Bowshock : 14.8R E ->13.5R E Location of Dayside Magnetopause : 11R E -> 9R E

16. Bz = -2 nT, Nsw = 5/cc Bz = -10 nT, Nsw = 10/cc Tail reconnection ~12 R E Earthward flow has ~75 km/s, while the tailward flows ~150km/s (20 min) (  P~40) little change J  (  J~6) Vx > 0 tailward Vx < 0 earthward

17. Summary We have studied magnetospheric phenomena by 3D MHD simulation when the IMF Bz and solar wind components exist. a)IMF Bz=-2nT, density=5/cm -3 -> IMF Bz =-2nT, density =10/cm -3 A large viscous cell near the magnetopause but very little convection in tail Tail reconnection occur at 14-15R E after 20 min Earthward flow ~ 40 km/s and tailward flow ~150km/s) Location of Bowshock ~14R E and Magnetopause location ~ 10R E Small tail current b) IMF Bz=-10nT, density=5/cm -3 -> IMF Bz=-10nT, density = 10/cm -3 A large convection in tail (after 15 min) Tail reconnection occur at ~11 R E Earthward flow ~300 km/s, while the tailward flows ~400km/s (10min) Bowshock ~ 13R E and Magnetopause ~9R E Tail current increase about 3times Condition 1 Condition 3 IMF Bz=-2nT, density=5/cm -3 -> IMF Bz=-10nT, density = 10/cm -3 very little convection in tail (after 20 min) Tail reconnection occur at ~12 R E Earthward flow ~70 km/s, while the tailward flows ~150km/s Location of Bowshock ~ 13.5R E and Magnetopause ~9R E Small tail current

18. Thank you very much for your attention

19. t pulse -5m t pulse +5m t pulse +10m t pulse +15m t pulse +20m Bz = -2 nT Nsw = 5/cc Bz = -2 nT Nsw = 10/cc Bz = -10 nT Nsw = 10/cc Different pulse condition

20. t pulse -5m t pulse +10m t pulse +15m t pulse +20m Bz = -2 nT Nsw = 5/cc Bz = -10 nT Nsw = 5/cc Red (dawn to dusk ) Blue (dusk to dawn) Time evolution of the electric field Simulation Results Bz = -2 nT Nsw = 10/cc Bz = -10 nT Nsw = 10/cc a)very little convection in tail b) little convection in tail 30 20 -60 X 0 -20 Y 0 (R E ) Condition 2

21. Bz = -10 nT Nsw = 10/cc Bz = -2 nT Nsw = 5/cc Bz = 0 nT Nsw = 5/cc Bz = -10 nT Nsw = 10/cc Condition 3Condition 4