Kinematic properties of the F region ion velocity field inferred from incoherent scatter radar measurements at Arecibo

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Abstract
A new multiple‐frequency incoherent scatter observing technique has improved the precision of F region ion velocity measurements at Arecibo. This technique makes it possible to analyze velocity data without making the assumption that the horizontal gradients in each component of the velocity vector are zero. By assuming that spatial gradients in ion velocity are constant and that the magnetic field line through the F region is equipotential it is possible to determine completely the variation of the ion velocity vector in the plane of the magnetic meridian. The horizontal divergence of the velocity vector is generally observed to be small. At night the most significant spatial variation in the ion velocity field is usually converging flow parallel to the magnetic field; this reverses to diverging flow in the daytime. Neglect of these horizontal gradients in the vertical ion velocity can result in systematic errors in the evaluation of the meridional ion velocity as large as 30 m s−1.