Calibration and assessment of Swarm ion drift measurements using a comparison with a statistical convection model

The electric field instruments onboard the Swarm satellites make high-resolution measurements of the F-region ion drift. This paper presents an initial investigation of preliminary ion drift data made available by the European Space Agency. Based on data taken during polar cap crossings, we identify large offsets in both the along-track and cross-track components of the measured ion drift. These offsets are removed by zeroing drift values at the low-latitude boundary of the high-latitude convection pattern. This correction is shown to significantly improve agreement between the Swarm ion drift measurements and velocity inferred from a radar-based statistical convection model for periods of quasi-stability in the solar wind and interplanetary magnetic field. Agreement is most pronounced in the cross-track direction (R = 0.60); it improves slightly (R = 0.63) if data are limited to periods with IMF B-z < 0. The corrected Swarm data were shown to properly identify the convection reversal boundary for periods of IMF B-z < 0, in full agreement with previous radar and satellite measurements, making Swarm ion drift measurements a valuable input for ionospheric modeling.