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5160 - AFP - Arecibo P.R. Fabry-Perot
Instrument Type: Instrument > OpticalInstrument > Interferometer > FabryPerot
Observatory: None
Observation Site: AFP - Arecibo P.R. Fabry-Perot
Operating Mode:

Instrument Page: AFP

The Arecibo Observatory Fabry-Perot interferometer (18.35N, 66.75W) has been in operation since 1972. The data reported here (1980-1988), are atomic oxygen measurements at 630.0 nm. According to the IGRF model, the magnetic declination angle at Arecibo varied between -9.4 and -10.4 degrees between February 1980 and July 1988, while the inclination angle varied between 48.8 and 47.9 degrees. All nights are clear, or had cloudy periods removed. The approximate emission height is assumed to be 300 km. Scans in azimuth were done at a 30 degree elevation height, with usually one zenith measurment per scan. The intensities are relative, (Code 2505) but are approximately correct to within a factor of two of the true emission intensities in Rayleighs. The Doppler half-width is related to the square root of the neutral temperature assuming a Gaussian emission shape. The instrument was not optimized to measure Doppler widths, but was broadened to increase the signal throughput in order to make better measurements of the Doppler shift, which is related to the neutral velocity. Because of uncertainties in the half-width, the conversion to temperature was not made. In some of the data files the zenith observations were used as a zero reference in the analysis (Code 4050=1), while for others, all of the measurements for a given night were used (Code 4050=0) by assuming that each component of the horizontal neutral wind velocity can be represented by a second order Taylor expansion (constant horizontal velocity gradients) about a point directly above the station. A harmonic analysis gives the zonal (Ue) and meridional (Un) velocities, and two parameters related to the deformation of the flow, d(Ue)/dx and d(Un)/dy, where x and y are the eastward and northward directions, respectively. The vertical wind velocity (Uz) is thus not measured directly, but is derived from the DC term of the expansion. Values of Uz are inferred as the product of the horizontal divergence of the horizontal wind velocity, Uh, and the neutral scale height H: i.e., Uz = H del(Uh) where H = 50 km.