For the VLF experiments, the 0 dB reference level is taken for convenience to be 10 33 T2 Hz 1 (equivalent to a power spectral density of 2.4 × 10 19 W m 2 Hz 1), the same reference as used for Ariel-3 and 4 (Bullough et al., 1969).
The Fabry-Perot interferometer only operates through periods of darkness and when the sky is clear. These key parameter data are therefore only available from April to September each year.
The H, D and Z components of the geomagnetic field at Halley are supplied as key parameters. For reference, the declination at Halley is about 1 W. The quiet day curve used to determine riometer absorption is determined for each day from the previous 30 day data sample.
The key parameters obtained from the SuperDARN radars are described in detail by Greenwald et al. (1995). For SHARE, the Halley radar currently provides velocity information to 30 locations spaced in 0.5 latitude steps along the magnetic meridian with a typical time resolution of about 2 min. The latitude at which the data set commences is variable, dependent on the location of backscatter for the scan in question. The data provided may be either the line-of-sight velocity or an estimate of the horizontal vector (determined in one of several ways). A data flag accompanying each scan will indicate which type is provided. When the Sanae radar commences operation, a similar key parameter set will be provided for it, plus vector flows determined from dual operation and computed for the Halley magnetic meridian.