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

4 Space Weather Magnetic Substorms This spectrogram shows the history of energetic electron fluxes sampled by the geosynchronous satellite ATS 6 on 29 July Jagged peaks mark the arrival of electrons in 3 substorms, and they gradually drift away again. Lower energy (~ 1000 eV) electrons that persist belong to the plasma sheet in which the satellite is immersed for about half of its orbit. High-energy substorm injection population can lead to dangerous levels of spacecraft charging, especially when in eclipse at substorm onset

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 InO 3 paint

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

7 Space Weather Magnetosphere-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 Weather Magnetosphere-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 Weather Magnetosphere-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 inputs to 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/cm 2 -s = mW/m 2

10 Space Weather Magnetosphere-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 law equation with given ionospheric conductivity distribution.

12 Space Weather Magnetosphere-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.