Space Weather: The Aurorae

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

Space Weather The Aurorae

Kristian Olaf Bernhard Birkeland

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1867: born in Kristiania (Oslo) 1880 - 1890: High school and university education 1893 - 1895: Postgraduate Research in France & Germany - published 1 st generalized solution of Maxwell equations - characterized electric sparks (telegraphic applications) - began cathode ray experiments (Röntgenstrahlen) 1897: elected member of The Norwegian Academy 1898: appointed Professor of Physics (by King Oscar II of Sweden) 1917: died in Tokyo 88 scientific papers (more than 50 in Comptes Rendus) 3 books describing his arctic expeditions 60 patents (electromagnetic cannon/artificial fertilizer) 3

Space Weather The Aurorae

Birkeland’s Terrella Simulations:

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Concept:

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Cathode rays fired at a magnetized sphere

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Light emissions surround magnetic pole like aurorae

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Experimental Results:

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Birkeland’s Interpretation: Energetic electrons (cathode rays ) from the Sun are “sucked” into Earth’s magnetic field and reach the upper atmosphere where they excite optical emissions.

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Does interpretation make sense?

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Space Weather The Aurorae

Norwegian Polar Expeditions

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1897 Campaign to Kåfjord Total disaster in surprise early autumn blizzard, T => -25° C; student severely injured

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1899-1900 Campaign to Kåfjord

Constructed 2 auroral observatories at tops of Mts. Haldde and Talvik, separated by 2.7 km but connected via telephone line Measured magnetic perturbations associated with overhead aurora Separation too small to estimate heights of aurorae by parallax Student Elisar Boye killed in an avalanche 5

Space Weather The Aurorae

Norwegian Polar Expeditions

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1902 – 1903 Campaign: 4 Stations:

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Supplies, sled dogs and coal Kåfjord, Norway Dyrafjord, Iceland Axeløen, Svalbard Matotchkin, Novaya Zemlya Inter-station separation of about 1000 km All stations equipped with:

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Magnetometers and calibration sensors Electrometers to measure atmospheric conductivity and Earth currents Meteorological sensors to measure P, T and V All personnel had to have experienced wintering over in the Arctic 6

Space Weather The Aurorae

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Norwegian Polar Expeditions 1902 – 1903 Campaign Results:

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Analyzed many magnetometer traces and auroral optical images to demonstrated that disturbances span wide regions of the globe and identified characteristics of magnetic storms and substorms.

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NAPE volumes 1 and 2 published in 1908 and 1913: 801 pages in English Estimated that millions of Amperes flow into n the upper atmosphere during disturbances.

Argued that such large currents must be driven by Sun and transmitted via field-aligned currents.

After decades of hot debate field-aligned currents first observed by TRIAD satellites in 1967 7

Space Weather The Aurorae

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Fredrik Carl Mülertz Størmer

1874: born in Skien 1887 - 1897: High school and university education (1 st publication while still in HS) 1898 - 1900: Postgraduate Research in France & Germany - published about 10 paper in pure mathematics 1902: elected member of The Norwegian Academy 1903: appointed Professor of Pure Mathematics by Kink Oscar II 1904: begins particle trajectory in magnetic dipole calculations 1910, 1913: auroral expeditions to Bossekop 1957: died in Oslo ~ 300 scientific papers (more than 50 in Comptes Rendus) Auroral Atlas (1930, 1934, 1951) and The Polar Aurora (1953) 4 nominations for Nobel Prize in Physics with Kr. Birkeland 8

Space Weather The Aurorae

Størmer's Contributions to Auroral Physics:

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Calculated trajectories of energetic charged particles in dipole representation of Earth’s magnetic field Enticed by Birkeland’s terrella experiments (1904) Reduced trajectory equations to those of a particle facing a potential barrier then obtained all possible solutions numerically (by hand calculkations) Demonstrated forbidden and allowed regions

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Cosmic ray access to Earth Van Allen radiation belts Predicted ring current during magnetic storms 9

Space Weather The Aurorae

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Størmer's Contributions to Auroral Physics:

Determined auroral heights classes and locations

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With Krogness developed first camera to photograph aurorae Conducted auroral expeditions to Bossekop in 1910 and 1913 Developed physical /analytical tools to conduct parallactic measurements of auroral features

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Established auroral network in southern Norway Aurorae do not penetrate below 90 km, can reach 1,000 km Align in the magnetic east-west direction Normally near magnetic latitudes of 67° but in storms move to about 57° 10

Space Weather The Aurorae

Homogeneous arcs Reflected image Break up Red aurora with rays Corona Upwards or downwards?

Rayed band 11

Space Weather The Aurorae

Some Conclusions

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Long before entry into space European scientists were investigating phenomena that occur in the atmosphere above 100 km that reflect the variability of our space environment Birkeland’s field-aligned current model first suggested how energy from the Sun electrically couples to Earth’s upper atmosphere.

Størmer's analysis of allowed particle trajectories anticipated properties cosmic rays and the radiation belts discovered decades later.

Størmer's parallactic photography provided the first systematic basis for understanding the structure and chemistry of the upper atmosphere. 12