Space Weather: Magnetosphere-Ionosphere Coupling Overview

1. C/NOFS DMSP Space Weather: Magnetosphere-Ionosphere Coupling 14 November 2011 William J. Burke Air Force Research Laboratory/Space Vehicles Directorate Boston College Institute for Scientific Research CRESS

2. Space Weather Course Overview • Lecture 1: Overview and Beginnings • Lecture 2: The Aurorae • Lecture 3: Basic Physics (painlessly administered) • Lecture 4: The Main Players • Lecture 5: Solar Wind Interactions with the Earth’s Magnetic Field • Lecture 6: Magnetic Storms • Lecture 7: Magnetic Substorms • Lecture 8: Magnetosphere – Ionosphere Coupling • Lecture 9 The Satellite Drag Problem • Lecture 10: Verbindung (to help make up for your rash decision not to take Wollen Sie Deutch Sprechen?)

3. Space WeatherMagnetosphere-Ionosphere Coupling Overview • This week we will try to accomplish two things: • 1. Finish our consideration of substorms in terms of their effects on satellites, especially near geostationary altitude. • 2. Introduce the concept of M-I coupling • There are two manifestations of spacecraft charging: (1) on surfaces and (2) inside dielectric materials such as insulation material on electric wires. • The Tethered Satellite System (TSS) missions • “M-I coupling” can mean different things to different people or even different things to the same people, albeit at different times. • Coupling can be effected by exchanges of particles , e.g. the aurora • More importantly, M-I coupling often refers to electromagnetic connectedness between these two regions of space. • Big electric circuit in the sky

4. Space Weather Magnetic Substorms

5. Space Weather Magnetosphere-Ionosphere Coupling • Conceptually, spacecraft charging is very simple: Surface potentials go to the levels with respect to plasma ground where the net current is zero. • In practice it can get rather complicated: - Plasma environment (hot and/or cold) • - Solar illumination creates photoelectron emissions: mitigates charging. • - Conductance and secondary emission characteristics of surface materials • - Active/passive techniques to control of charging environments • Beam/plasma emissions • Satellite coating with transparent but conducting InO3 paint

6. Space WeatherMagnetosphere-Ionosphere Coupling • Danger: • Differential Charging • Arcing between elements • Monitors threats due to: • Total Radiation Dose • Radiation Dose Rate • Deep Dielectric Charging • Single Event Effects Compact Environmental Anomaly SEnsor (CEASE)

7. Space WeatherMagnetosphere-Ionosphere Coupling • The Tethered Satellite System: NASA and Italian Space Agency to test feasibility of converting mechanical to electric energy. • Mission concept: deploy conducting tether upward by ~ 22 km. • Generate > 5 kV drops along tether between satellite and shuttle. • Murphy’s Law: TSS-1 Tether release mechanism jammed • TSS-1R Tether self immolated and broke. Tether Structure 

8. Space WeatherMagnetosphere-Ionosphere Coupling Coupling via Charged Particle Exchange • Auroral (keV) precipitation from plasma sheet: • - Creates new ionization in ionosphere (< 1eV) • - Produces low-energy secondary electron population • - Excites visible emissions from atomic/molecular constituents • Plasma outflows from ionosphere to magnetosphere at all latitudes

9. Space WeatherMagnetosphere-Ionosphere Coupling Auroral Energy Particle Inputs to Ionosphere Dave Evans and colleagues at NOAA in Boulder CO used POES and DMSP data to systematize auroral electron energy inputsto auroral oval as a function of the planetary index Kp. - At highest level (Kp = 9), hemispheric power ~ 350 GW almost an order of magnitude below stormtime electromagnetic (EM) energy input that heats the ionosphere/thermosphere . - Ionization by auroral particles enhances and limits EM heating efficiency. Energy Flux in ergs/cm2-s = mW/m2

10. Space WeatherMagnetosphere-Ionosphere Coupling The Large-Scale Circuits of M-I System • Often a student’s first encounter with the M-I system in the form of a large and bewildering array of electric current circuits. • In different ways they indicate how Maxwell’s equations describe different particle and magnetic field environments found in our near-Earth space. • For M-I coupling, the system of field-aligned currents is most important.

11. Space Weather Magnetosphere-Ionosphere Coupling Field aligned Current Systems • Satellite studies show that FACs come in large and small scale sizes. - Discrete auroral arcs have their own systems, out of the ionosphere within the arc and upward on its equatorward boundary (< 10 km). • - Large (> 100 km) scale FACS divide into two regions: • Region 1 flows near the poleward boundaries of auroral oval , • into of the ionosphere on the dawn side and out on the dusk side • Region 2 flows near the equatorward boundaries of auroral oval, • into of the ionosphere on the dusk side and out on the dawn side • - Potential distributions in global ionosphere and magnetosphere obtained by solving Ohm’s lawequation with given ionospheric conductivity distribution.

12. Space WeatherMagnetosphere-Ionosphere Coupling Summary and Conclusions • In this lecture we first considered severe spacecraft charging environments produced near geostationary altitude. • - Electrons with energies > 7 keV cause kV charging • - Differential charging can lead to electric arcing • - AF and NASA developed techniques to mitigate threat. • - Deep dielectric charging by electrons with E > 50 keV leads to current surges that disrupt s/c command & control. • Plasma sheet/auroral particles pour energy into ionosphere: • - Power input increases non linearly with magnetic activity • Large scale field-aligned currents couple the M-I system - Control electric field patterns in the ionosphere • and magnetosphere, even in current source regions. • Discrete auroral arcs have their own small scale FAC system.