1. Solar wind-magnetosphere coupling Magnetic reconnection In most solar system environments magnetic fields are “frozen” to the plasma - different plasmas cannot mix At thin boundaries the frozen-in approximation can break down, leading to magnetic reconnection and plasma, momentum and energy exchange between otherwise segregated regions

2. Solar wind-magnetosphere coupling Open magnetosphere Magnetic reconnection results in an “open” magnetosphere Where reconnection occurs on the magnetopause depends on the relative orientation between the incoming interplanetary magnetic field (IMF) and field lines at the magnetopause open closed current sheet

3. Solar wind-magnetosphere coupling Reconnection location IMF B z < 0, B y = 0 IMF B z > 0, B y > 0 Reconnection with closed field lines Reconnection with open field lines

4. Solar wind-magnetosphere coupling The open magnetosphere and the Dungey cycle for IMF B z < 0 nT

5. Aurora at the footprint of these field lines are the signature of plasma entry due to reconnection

9. Tail reconnection occurs explosively in a process known as the substorm - Earth’s most intense aurorae occur here

13. Ionospheric convection Measurements of the ionospheric plasma convection show that field lines remain open for 4 hours and closed for 8 hours A solar wind speed of 450 km s -1 implies that the magnetotail is ~1000 R E in length The size of the “polar cap” determines the amount of magnetic flux in the “lobes” This in turn allows the radial dimension of the magnetotail to be estimated at ~25 R E

14. Plasma populations in the magnetosphere The solar wind (mainly H + and e - ) populates the hot, low density (~ 1 cm -3 ) “plasma sheet” This is in pressure balance with the very low density (~0.01 cm -3 ) lobes magnetosheath bowshock

15. Plasma populations in the magnetosphere The ionosphere populates the cold, high density (~ 100 cm -3 ) “plasmasphere” (say, O + and e - ) Outside of this region, very high energy particles comprise the Van Allen belts

16. Plasma populations in the magnetosphere Magnetosheath Plasmasphere Plasma sheet Ring current