Space Weather: The Aurorae

26 September 2011

William J. Burke

Air Force Research Laboratory/Space Vehicles Directorate

Boston College Institute for Scientific Research

DMSPC/NOFS

CRESS

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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: Magnetosphere – Ionosphere Interactions

• Lecture 7: Solar Induced Disruptions

• Lecture 8: Magnetic Storms and Substorms

• Lecture 9The 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 WeatherThe Aurorae

• 1867: born in Kristiania (Oslo)

• 1880 - 1890: High school and university education

• 1893 - 1895: Postgraduate Research in France & Germany - published 1st 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 expeditions60 patents (electromagnetic cannon/artificial fertilizer)

Kristian Olaf Bernhard Birkeland

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Space Weather The Aurorae

– Concept:

– Experimental Results:

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

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Birkeland’s Terrella Simulations:

• Cathode rays fired at a magnetized sphere

• Light emissions surround magnetic pole like aurorae

Does interpretation make sense?

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Space Weather The Aurorae

• 1897 Campaign to Kåfjord

• Total disaster in surprise early autumn blizzard, T => -25° C; student severely injured

• 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

Norwegian Polar Expeditions

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Space Weather The Aurorae

• 1902 – 1903 Campaign: 4 Stations:

– Supplies, sled dogs and coal

– Kåfjord, Norway

– Dyrafjord, Iceland

– Axeløen, Svalbard

– Matotchkin, Novaya Zemlya

• All stations equipped with:

– 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

Norwegian Polar Expeditions

Inter-station separation of about 1000 km

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Space Weather The Aurorae

• 1902 – 1903 Campaign Results:

– Analyzed many magnetometer traces and auroral optical imagesto demonstrated that disturbances span wide regionsof the globe and identified characteristics of magnetic storms and substorms.

– NAPE volumes 1 and 2 published in 1908 and 1913:801 pages in English

– Estimated that millions of Amperes flow inton 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

Norwegian Polar Expeditions

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Space Weather The Aurorae

• 1874: born in Skien

• 1887 - 1897: High school and university education (1st 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

Fredrik Carl Mülertz Størmer

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Space Weather The Aurorae

• 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 particlefacing a potential barrier then obtained all possible solutions numerically (by hand calculkations)

• Demonstrated forbidden and allowed regions

• Cosmic ray access to Earth

• Van Allen radiation belts

• Predicted ring current during magnetic storms

Størmer's Contributions to Auroral Physics:

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Space Weather The Aurorae

• Determined auroral heights classes and locations

– 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

– 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°

Størmer's Contributions to Auroral Physics:

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Space Weather The Aurorae

Homogeneous arcs

Corona

Break upReflected image

Red aurora with rays

Rayed bandUpwards or downwards?

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Space Weather The Aurorae

• 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.

Some Conclusions