Plasmasphere Last time we started talking about: Why does the plasmashere corotate? Review hot, cold drifts Discuss Alfven Shielding Layer Put it all together Then introduce Ionosphere subjects Plasma density 100 or 1000 times higher than outer magnetosphere Field Aligned Currents Region 1 (inner) Region 2 (outer) Ijima&Potemera Now, lets put it together • How do we explain Region 1 and Region 2 field aligned currents? • Region 1 is driven by magnetopause charge separation • Region 2 is driven by partial ring current • Next: what about aurora? Partial Ring Current: energetic particles Grad- B drift but don’t make it all the way around the earth Equatorial Plane View Plasmasphere corotates with Earth once a day Equatorial Plane View Plasmasphere corotates with Earth once a day Magnetic activity index Very High Density Moving from magnetosphere to ionosphere • Field aligned currents • Ionosphere structure • Ionosphere currents, What is σ? – 1. below 85 km altitude σ is isotropic – 2. 85 to 150 km (D and E regions) σ is tensor – 3. above 150 km σ is just σ|| • Then: put it all together Three views of ionosphere structure • Electron density • Thermal structure • Ion density and source Free electrons e- Negative ions Ionsopheric currents • J = σ E Ohms Law • We know there are large scale E fields (why), so what is σ in the ionosphere? What is Conductivity? • The scalar conductivity σ is defined as the ratio of the current density to the electric field strength σ = J/E. For a resistive medium this is just the Spitzer conductivity: • To get the components look at • So, σ can have many components: (Another way to derive scalar conductivity) Conductivity when particles gyrate σ becomes a matrix .