Millstone Hill incoherent scatter observations of auroral convection over 60° ≤Λ≤75°, 1. Observing and data reduction procedures

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Abstract
The Millstone Hill radar, Westford, Massachusetts (Λ = 56°), has been upgraded for observations in support of the international magnetosphere study by means of the addition of a 150‐foot‐diameter fully steerable antenna. This antenna allows measurements of F region ion drifts, from which F region electric fields can be derived, using the existing UHF (68‐cm wavelength) radar. The paper describes attempts to measure the electric field in the auroral zone over the interval 60° ≤ Λ ≤ 75°. This effort entails making observations to the north of Millstone at very low elevation angles over periods of ≥24 hours. To secure estimates of both the E‐W and the N‐S components of the drifts, the measurements are made in two directions separated by ±15° from the magnetic meridian, and to achieve the desired coverage in latitude, measurements must be made at two elevation angles for each of these azimuths. The separation in time and space of the two components of the drift that are observed introduces a difficulty in interpreting the results. This has been overcome by matching the observations, in a least mean squares sense, by analytical functions describing the components of the electric field, each of which has 102 degrees of freedom. The results obtained thus represent the variation of the auroral electric fields over 24 hours local time smoothed with respect to both latitude and time. The utility of this approach is illustrated using sample results for one moderately quiet day, and the resolution and accuracy of the method are discussed.