IGY Bulletin, Number 3, September 1957 - Geomagnetic Program

Geomagnetism (at least some aspects of it) was basically my own area of geophysical expertise. So I am going to give you a little history of my former areas of research, add a little tutorial of geomagnetism and paleomagnetism, and then summarize the contents of this IGY Bulletin article. Some of this material has come up in previous posts, but I won't cross-reference them.

After my B.S. in engineering physics at Cornell, I worked for two years for Fairchild Space and Electronics on satellite power subsystem analyses (solar cell arrays and rechargeable batteries). When I decided to go back to grad school, I wanted an area of applied physics that would allow me to pursue either more academic topics or applications to more "practical" problems. Geophysics, as I hope this blog has already shown, is chock full of academic problems. But geophysics also includes a suite of techniques useful in oil and minerals exploration, so I knew there was always that. Some would call this distinction "pure" vs. "applied" geophysics. I explored applied geophysics in corporate settings when, during grad school, I worked one summer for Amoco (oil), and another summer and part-time job with Newmont (mining). But in the end, I chose the academic route for my career.

Starting in my first year of grad school in geosciences at the University of Arizona, my research assistantship with Paul Damon on radiocarbon geophysics involved computer modeling of relationships between the Earth's magnetic field strength and production of carbon-14 by cosmic ray induced spallation in the atmosphere. At the same time, I took courses in geomagnetism and paleomagnetism from my second great academic mentor, Dr. Robert Butler, a gifted instructor and researcher. He then supervised my master's thesis and Ph.D. dissertation on archaeomagnetism (Sternberg, 1990): the use of baked clay archaeological materials (hearths and ceramics) to yield information on the past direction and strength of the magnetic field in the American Southwest. Time changes of the internal part (see below) of the magnetic field on the order of decades/centuries/millennia are called secular variation. Archaeomagnetism can also be used as an archaeological dating method by matching results from new features to these patterns of secular variation. 

Later in my career, I also used magnetic exploration methods (Burks, 2018) at various archaeological sites -- Pennsylvania, New York, Georgia, Jamaica, Greece, Italy, Azerbaijan -- to search for buried features and to delineate archaeological activity areas. Towards the end of my career, I examined magnetic properties of obsidian artifacts from New Mexico and Italy to see if their magnetic properties could be matched to geologic obsidian sources.

The Earth's magnetic field has an internal and an external component. The majority of energy resides in the internal magnetic field, which is depicted below. 

A schematic of an approximation to the Earth's internal magnetic field, having the shape of a dipole (bar magnet) tilted relative to the Earth's rotation axis

Einstein once called the origin of the Earth's magnetic field one of the greatest unsolved problems in physics (nor just geophysics), In the late 1940s, it was proposed that it is generated by dynamo action in the swirling electrically conducting molten iron fluids of the Earth's outer core. Changes of these fluid motions are responsible for the phenomenon of secular variation, and also reversals of the magnetic field which typically occur a few times per million years. Rocks can record information about ancient magnetic fields and preserve these like a tape recorder. These records of ancient magnetic fields and their application to geologic problems like continental drift comprises the field of paleomagnetism, of which archaeomagnetism is part. Paleomagnetism has developed greatly since the era of the IGY.

The geomagnetism studies of the IGY were focused on the external part of the Earth's magnetic field, which is due to charged particles moving in the ionosphere, much as an electrical current in a loop of wire will generate a magnetic field due to the Biot-Savart law. These charged particles emanate from the solar wind, then pass into the asymmetric magnetosphere (geomagnetic field) carved out of the interplanetary magnetic field, with the magnetopause being the boundary.

Schematic of the Earth's magnetosphere (Bagenal and Bartlett), encompassing the dipole field shown above

So, back to the article in the IGY Bulletin. If I understand correctly, it makes an error or at least poor choice of words. It states "analysis has shown that the very slow variations [secular variation] are due to the magnetic effects in the interior of the earth's crust and that the more rapid fluctuations arise from influences external to the earth -- in the upper atmosphere or even higher." So, the internal part of the geomagnetic field and secular variation derives from the core, which is below but not "in the interior of" the crust. But the distinction between rapid external field variations and slower internal field changes is useful and important.

The U.S. currently has 14 geomagnetic observatories, eight of which were in operation during the IGY.  A major goal of the IGY effort was to study magnetic storms related to solar activity. At that time, the correlation was clear, but the mechanism by which these phenomena were connected was not well understood. Additional regional networks of stations to record magnetic field information were established for the IGY. Measurements were taken every few seconds, using all the vector components (north-south, east-west, and up-down) of the magnetic field. Stations were set up on the magnetic equator, at U.S. Antarctic stations, and at Drifting Station A in the Arctic. It was anticipated that rockets and maybe even satellites would carry magnetometers (instruments to measure the magnetic field) higher up into the magnetosphere during the IGY.