space weather: magnetosphere-ionosphere coupling 14 november 2011 william j. burke air force...

Space Weather: Magnetosphere-Ionosphere Coupling

14 November 2011

William J. Burke

Air Force Research Laboratory/Space Vehicles Directorate

Boston College Institute for Scientific Research

DMSPC/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 WeatherMagnetosphere-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 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

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


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


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


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


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


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


Field aligned Current SystemsSatellite 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


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.

space weather: magnetosphere-ionosphere coupling 14 november 2011 william j. burke air force...

Documents