Instruments:hfp

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Halley Fabry-Perot

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Acknowledgments

The Halley Fabry-Perot Interferometer is operated by the British Antarctic Survey which is part of the United Kingdom's Natural Environment Research Council (NERC).

Instrument/Model Description

A Fabry Perot Interferometer is operated by the British Antarctic Survey at Halley, Antarctica. The station is sited on a floating ice shelf that drifts westward at around 800 m per year, requiring a new station to be built further to the east about every 10 years or so. The geographic coordinates are 75.5 deg S, 26.6 deg W, and the invariant geomagnetic coordinates are 61.5 deg S, 28.9 deg E. The magnetic inclination is 64 deg and magnetic north is 2 deg west of geographic north. The mean local time is 1 hour and 46 minutes (-26.6/15.) before Universal Time. The station was closed in 1998.

All the Halley data have been obtained by observing the 630 nm emission line from atomic oxygen, and are therefore representative of an altitude of around 240 km. Measurements of the line of sight velocities are made for 300 sec in the zenith and at 30 deg elevation looking in the cardinal directions. Over a half hour the sequence is: calibration, west, south, zenith, and north. The line of sight velocities at 30 deg elevation are converted to horizontal velocities by assuming that the vertical velocity is zero. A cubic spline interpolation is used to calculate the velocities at 0, 15, 30 and 45 minutes past each hour.

A zero reference velocity is obtained by assuming that the mean vertical wind over the whole night is zero. Every zenith observation made is used to calculate this zero, irrespective of cloud cover. In this set, data is provided only if the cloud cover is 3 oktas or less. Data is also eliminated if it was not possible to determine the velocities in certain directions due to poor quality spectra. Hence, on several nights, data is available for only a limited period of time. Because of this, the mean vertical velocity of the proided data is not zero. Errors are not calculated for each individual measuerment but are typically 20-30 m/s.

John Emmert of NRL found in 2005 that the 1994-1995 data for +E and +N winds were actually +S and +W winds. This is shown in his .pdf plot of the yearly average data as a function of the solar flux, where MWIND is the meridional wind (+N) and ZWIND is the zonal wind (+E). The 1994 and 1995 data are solar minimum conditions and are wrong, where MWIND is +W and ZWIND is +S. A second .pdf plot shows the corrected 1994-1995 MWIND and ZWIND data. The error arose when the 1994-1995 data were listed as being +S and +E, but were actually in the order +E and +S. There was one operator for 1994-1995, and also a sequencing change between 1995 and 1996. The 1994-1995 data were corrected in direction in January 2006 at the request of Martin Jarvis of BAS.

Summary plots of the horizontal and vertical winds are plotted for 10 days at a time. The data in the CEDAR Data Base are nighttime winter measurements from 1988 to 1993 that were submitted by Roger Crickmore.

References for the instrument and data processing procedures

Stewart, R. D., R. W. Smith, D. Rees, J. R. Dudeney, and A. S. Rodger, First measurements of thermospheric winds in Antarctica by an optical ground-based method, Nature, 317, 45-48, 1985.
Stewart, R. D., A. S. Rodger and J. R. Dudeney, Thermospheric response to the magnetic signature of the Harang Discontinuity, Planet. Space Sci., 36, 225-229, 1988.
Smith R. W., D. Rees and R. D. Stewart, Southern hemisphere thermospheric dynamics: A review, Rev. Geophy., 591-622, 1988.
Crickmore R. I., J. R. Dudeney and A. S. Rodger, Vertical thermospheric winds at the equatorward edge of the auroral oval, J. Atmos. Terr. Phys., 53, 485-492, 1991.
Crickmore R. I., A comparison between vertical winds and divergence in high latitude thermosphere, Ann. Geophys., 11, 728-733, 1993.
Crickmore R. I., Mean thermospheric winds observed from Halley, Antarctica, Ann. Geophys., 12, 1101-1113, 1994.
Crickmore R. I., A study of the thermospheric forces at a high latitude site on two days of differing geomagnetic activity, J. Atmos. Terr. Phys., 57, 759-773, 1995.

Summary Plots for Halley Fabry-Perot in OI (6300 A)

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-Revised 13 Jan 2006 by Barbara Emery

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