Abstract
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.
Highlights
The Swarm satellite mission is aimed at providing a survey of the geomagnetic field and a global representation of its variation on timescales from hours to years (FriisChristensen et al 2006, 2008)
The lowlatitude boundary is defined as the Heppner–Maynard Boundary (HMB) corresponding to the CS10 statistical convection model for the solar wind and interplanetary magnetic field (IMF) conditions that exist during the satellite pass
Offsets in the original Swarm ion drift data were removed by zeroing each component of the measured ion drift at the equatorward edge of the convection zone as defined by the Heppner–Maynard boundary corresponding to the CS10 statistical convection model for that period
Summary
The Swarm satellite mission is aimed at providing a survey of the geomagnetic field and a global representation of its variation on timescales from hours to years (FriisChristensen et al 2006, 2008). Fiori et al (2013, 2014) have investigated techniques for estimating 2D plasma convection in the high-latitude ionosphere using Swarm data They showed that Swarm data can be incorporated into a spherical cap harmonic mapping algorithm that generates high-latitude convection maps from ground-based radar data. In both papers, data sets were artificially generated by considering statistical models to emulate ion drift measurements along hypothetical Swarm satellite tracks. The logical progression of this work is the testing of Swarm measurements, the comparison of Swarm data with plasma flow measurements from other instruments to ensure the data sets are suitable for merging, and the generation of convection maps
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