Earth's Magnetic Field - Charles Dodge

 

Earth's Magnetic Field

Earth's Magnetic Field

Realizations In Computed Electronic Sound

Bruce R. Boller, Carl Fredericks, Stephen G. Ungar, Scientific Associates

Produced at The Columbia Computer Center

Coordinator: Teresa Sterne

Art Direction: Robert L. Heimall

Cover Art: Gene Szafran

Cover Design: Paula Bisacca

Cover Concept: Hess and or Antupit

Nonesuch H-71250 STEREO

A Nonesuch Record Commission

From the front and back covers: Earth can truly be pictured as a giant magnet. Sir William Gilbert recognized this fact as early as 1600 in his book De magnete. The subtle consequences of the existence of Earth's magnetic field have not been realized until recently. In the last decade, satellite experiments have established the existence of a solar wind, continually emanating from the sun at speeds of several hundreds of miles an hour and engulfing all the planets.

The natural nuclear furnace deep within the sun provides energy that bathes the planetary system with heat and light, and also heats up the sun's atmosphere. As a result, the solar atmosphere expands rapidly outward into interplanetary space, becoming what is known as the solar wind.

If it were not for the magnetic field of Earth, the solar wind could intermix with the gases of our atmosphere. Since the solar wind is an electrically charged gas, the magnetic field is able to deflect it away at distances far greater than the extent of Earth's atmospheric layers.

The solar wind may be viewed as pushing against Earth's magnetic field, with the magnetic field, in turn, producing an equal but opposite push on the solar wind. The solar wind is not uniform and consequently any changes in it are quickly reflected at the Earth's surface as changes in the magnetic field. Occasionally, these magnetic changes are even large enough to deflect ordinary compass needles. In practice, specially designed instruments are continually operated all over the world to monitor these changes.

To indicate the average level of magnetic activity for Earth, the Kp index has been established. (The designation Kp is derived from an abbreviated form of the German word for "corpuscular": geophysicists at the turn of the century thought the cause of the magnetic variations to be solar particle radiation.) This index represents the average of the magnetic changes, which are measured at a selected group of magnetic observing stations on Earth and may take on any of 28 distinct values. Every three hours, the observations provide a new value for the index, thereby giving eight values of Kp for each day.

As an aid for researchers, the Kp indices are displayed graphically. They look somewhat like musical notation and are popularly called "Bartels' musical diagrams," after their inventor, German geophysicist Julius Bartels (1899- 1964). These diagrams are largely responsible for providing the motivation for the music contained in this album.

In addition to the Kp indices, the graphs indicate the times of occurrence of "sudden commencements." As the term implies, these are rapid changes of Earth's magnetic field. The sudden commencements are determined by an examination of the detailed data from each magnetic observatory. In a real sense, then, the music on this record represents the sun playing on the magnetic field of Earth.

The succession of notes in the music corresponds to the natural succession of the Kp indices for the year 1961. Musical interpretation of the magnetic data was originally conceived by Messrs. Boller and Ungar and implemented by Carl Frederick, the indices were computer-programmed into a form suitable for music synthesis by Stephen Ungar. This musical interpretation consisted of setting up a correlation between the level of the Kp reading and the pitch of the note (in a diatonic collection over four octaves), and compressing the 2,920 readings for the year into just over eight minutes of musical time.

An extended interpretation of the Kp index employed in shaping the music for this record embraces the pattern of sudden commencements during 1961. A graph, plotting the highest reading within each segment between the sudden commencements versus the relative length of the segment, was devised to delineate such attributes of the texture as tempo, dynamics, and register in both the larger and smaller dimensions of the work. An example of the use of this graph can be heard in the first section of the record where the tempo and dynamic changes reflect this graphing of the sudden commencements of the whole year; the pitch succession corresponds to the actual Kp readings between January 1 and February 4.

The single-line pitch successions on Side One exhibit the diatonic correspondence described above. The polyphonic settings of sudden-commencement sections which comprise Side Two employ an equal-tempered correspondence, with twelve Kp readings to the octave.

The musical realization of Earth's Magnetic Field was accomplished between June and September of 1970. The computer "instruments" for the performance were programmed by Charles Dodge, using a general-purpose sound synthesis program written by Godfrey Winham at Princeton University. The process by which computers can be made to "play" electronic sounds is distinct from and should not be confused with sounds created in electronic music studios or with synthesizers. (A description of this process may be found in the annotations to Nonesuch H-71245, Computer Music.) All of the sounds heard in this album were computed into digital form using the IBM/360 model 91 at the Columbia University Computer Center, and were converted to analog form at the Bell Telephone Laboratories. BRUCE R. BOLLER & CHARLES DODGE

CHARLES DODGE (b. 1942 in Ames, Iowa) studied composition at the University of lowa, at Tanglewood, and at Columbia University, where his teachers included Jack Beeson, Otto Luening, and Chou-wen Chung. From 1966, he studied electronic music with Vladimir Ussachevsky at Columbia and computer music at Princeton University with Godfrey Winham. He has earned degrees from the University of Iowa and Columbia University, from which he received his doctorate. Mr. Dodge has received numerous composition awards, as well as commissions from the Fromm and Koussevitzky Foundations, and from the Contemporary Music Society. He is now Assistant Professor in the Music Department of Columbia University, and is director of a research project in computer sound synthesis at the Columbia University Computer Center. Charles Dodge's composition Changes may be heard in the Nonesuch album H-71245, Computer Music.

BRUCE R. BOLLER (b. 1940 in New York) is currently a member of the Department of Physics at the City College of the City University of New York, from which he received his doctorate, and is engaged in research dealing with solar-terrestrial physics.

CARL FREDERICK (born in New York, raised in Australia) is a post-doctoral research associate with the NASA Goddard Institute for Space Studies in New York. An accomplished bagpiper who will admit under pressure to being at one time "a very bad violinist," Dr. Frederick is a physicist specializing in infra-red astronomy and general relativity.

STEPHEN G. UNGAR (b. 1937 in New York) is a lecturer in physics at the City University of New York. He is an astrophysicist and has had extensive computer-program- ming experience in connection with his field of specialization, the structure and evolution of stars.