Space Physics at Dartmouth College
LaBelle Group
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Space Physics at Dartmouth College LaBelle Group |
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South Pole, Antarctica
Instruments
Photos Main ScienceIn addition to it's location just poleward of the auroral zone, which is optimal for observing auroral roar radio emissions, South Pole Station has in principle a very low noise level since HF noise caused by human activities is limited to that arising from the station itself. Station noise is significantly reduced by placing the Dartmouth LF/MF/HF antenna 1.5 km from the station. Example science results from South Pole Station: Because of the low ambient noise level, it is possible to analyze data from South Pole Station in a semi-automated fashion; that is, the computer can be trained to recognized auroral radio emissions in the data. One full year (1999) of South Pole data have been analyzed in this manner, resulting in scatterplots of the local times, center frequencies, and amplitudes of all auroral roar events occuring during the year. These data reveal several interesting features. For example, they confirm that auroral roar emissions occur only under nighttime conditions, and that magnetic local time rather than geographic controls the emissions The large amplitude events show a bipolar distribution of center frequencies, evidence that a significant fraction of the events observed at ground-level originate in the topside ionosphere. The auroral roar occurrences can also readily be compared to summary data from other instruments such as the magnetometer and the VLF receiver; for example, superposed epoch analysis using the magnetometer or VLF data to identify substorm onsets shows that auroral roar emissions are more likely to be observed at ground-level preceding substorms rather than after substorm onset, a feature suspected previously based on case study evidence. For more details, see LaBelle and Weatherwax, 2002. Instrument | TopDartmouth Programmable Frequency Receiver (PFR) This receiving system consists of a loop antenna of approximately 10 square meters. The antenna response is a dipole, with the null in the horizontal plane oriented such as to eliminate the largest source of local interference. A low-noise preamplifier at the antenna has frequency response 100 kHz to above 5 MHz, and transmits these signals through a 50-ohm coaxial cable to the observatory as little as a few hundred feet or as much as a mile away, depending on the station. The PFR is a superheterodyne receiver tunable to 0-5 MHz using IF frequency of 10.7 MHz and crystal filter with bandwidth 7.5 kHz. The local oscillator is controlled directly by a PC running DOS. In the standard mode, frequency is stepped from 30 kHz to 5 MHz in 10-kHz steps, repeating the 498-frequency sequence each 2 seconds. Other programs are used on occasion, including faster frequency switching. In the standard mode, data are collected 20-24 hrs/day, archived on disk in the PC at the station, backed up onto CD-ROM monthly by a local operator, and mailed to Dartmouth (except at Arviat and Taloyoak, where data are backed up annually onto tape by visiting personnel from SED Inc.) For more information, see Weatherwax, A.T., Ground-based observations of auroral radio emissions, Ph.D. thesis, Dartmouth College, Hanover, N.H., 1994. Location of all South Pole instruments:
Complete List of Dartmouth Instruments Photos | TopPhotos courtesy of Shengyi Ye
Publications | Top46. Rosenberg, T.J., S. Singh, C.S. Wu, J. LaBelle, R.A. Treumann, U.S. Inan, and L.J. Lanzerotti, Correlated bursts of AKR and VLF emissions associated with a Type III solar radio noise event, J. Geophys. Res., 100, 281, 1995. 53. Yoon, P.H., A.T. Weatherwax, T.J. Rosenberg, and J. LaBelle, Lower ionospheric cyclotron maser theory: A possible source of 2fce and 3fce auroral radio emissions, J. Geophys. Res., 101, 27015, 1996. 66. LaBelle, J., Review of recent ground-level observations of terrestrial auroral radio emissions, Planet. Radio Emissions IV, ed. by H.O. Rucker, et al., Austrian Acad. Sci. Press, p. 283, 1997. 69. Hughes, J., and J. LaBelle, The latitude dependence of auroral roar emissions, J. Geophys. Res., 103, 14910, 1998. 70. LaBelle, J., A.T. Weatherwax, M.L. Trimpi, J. Perring, and U.S. Inan, HF auroral hiss observations at high geomagnetic latitudes, J. Geophys. Res., 103, 20459, 1998. 89. LaBelle, J., and A.T. Weatherwax, Statistical study of auroral roar emissions observed at South Pole Station, to appear in J. Geophys. Res., 2002. 90. LaBelle, J., and R.A. Treumann, Auroral Radio Emissions, 1. Hisses, Roars, and Bursts, to appear in Space Sci. Rev., 2002. Note: Numbers refer to Full Publication List Also Note: Most abstracts are freely available through NASA's Astrophysics Data System Bibliographic Services (ADS). Some are available locally. Full texts are only available to users within institutions that subscribe to the corresponding web-based journal. Links | Top
Note: Links courtesy of A.T. Weatherwax. |
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