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
C/NOFS
DMSP
Space Weather
Course Overview
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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?)
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Space Weather
Magnetosphere-Ionosphere Coupling
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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.
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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
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Space Weather
Magnetic Substorms
• This spectrogram shows the history of energetic electron fluxes sampled
by the geosynchronous satellite ATS 6 on 29 July 1974.
• 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
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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
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Space Weather
Magnetosphere-Ionosphere Coupling
Danger:
• Differential Charging
• Arcing between elements
Monitors threats due to:
Compact Environmental
Anomaly SEnsor
(CEASE)
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Total Radiation Dose
Radiation Dose Rate
Deep Dielectric Charging
Single Event Effects
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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
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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
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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/cm2-s
=
mW/m2
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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.
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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.
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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.
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