Tilghman, B. Noah

Biographical/Historical note

The Siple experiment was a Stanford, NSF funded, VLF- triggered emission experiment that took place from 1973 to 1988. Siple Station was established to perform experiments that actively probed the magnetosphere using very low frequency (VLF) waves. The Station included a 21.2 km dipole antenna located in Antarctica at 75.93 S, 84.25 W. Its location was selected because of various characteristics:

1. The 2 km thick ice sheet at Siple allowed the construction of an antenna with a relatively high efficiency. With a 100 kW source, the antenna could obtain radiated powers on the order of 1 kW, which was necessary for stimulating wave-particle interactions in the magnetosphere.

2. Siple's magnetic conjugate point was easily accessible, near the city of Roberval (also in Lake Mistassini), Quebec.

3. Siple, at L = 4.3, was close to the plasmapause, where wave-particle resonances were likely to occur at the transmitted frequencies.

4. Siple could be operated year-round [1].

5. The station was effectively isolated from major EM noise in the VLF spectrum.

The objective of the Siple transmitter was to produce various formats, which allowed for controlled experiments to answer specific questions regarding triggered emissions. The observed data after transmission included many unexplained phenomena. Some of the more obvious phenomena includes (but definitely not limited to): rising and falling emissions, wave growth, entrainment, and multiple-hop echos.

Between 1973 and 1978, Siple operated with a transmitter known as Zeus. The Zeus transmitter could operate at one frequency at a time at powers up to 100kW. In 1978, the transmitter was replaced by the Jupiter transmitter, which could operate at multiple frequencies simultaneously and 150kW. In 1986, a second dipole antenna was added to explore polarization effects [2]. The Siple experiment ceased operation after the Antarctic summer of 1988.

Two receiving stations were operated during the Siple experiment. The first was located at Roberval, Quebec. The gradual northwesterly drift of Siple's conjugate point due to the secular variation of the geomagnetic field and the increasing interference from local power lines required the movement of the receiver to Lake Mistissini, Quebec during the later years of operation.

References

1.R . A. Helliwell and J . P . Katsufrakis, Upper Atmosphere Research in Antarctica, Chapter 5, Controlled Wave-Particle Interaction Experiments, pp. 100-129, Number 29 in the Antarctic Research Series . American Geophysical Union, 1978.

2. R . A. Helliwell, "Vlf wave stimulation experiments in the magnetosphere from Siple Station, Antarctica," Review of Geophysics, vol. 26, no. 3, pp. 551-578, August 1988.

From the guide to the B. Noah Tilghman color transparencies and other materials documenting Antarctica, 1972-1974, (Dept. of Special Collections and University Archives)