Validity Study of the Swarm Horizontal Cross‐Track Ion Drift Velocities in the High‐Latitude Ionosphere

Abstract

High‐latitude ionospheric plasma convection plays a fundamental role in determining many processes in the terrestrial ionosphere. Electric Field Instruments on the European Space Agency's three polar‐orbiting Swarm satellites measure ionospheric ion drift velocities at about 500 km altitude using thermal ion imager energy/angle‐of‐arrival electrostatic analyzers. Recently, European Space Agency released horizontal cross‐track components of these drifts, calibrated at high latitudes. This paper concerns the validation of the Swarm horizontal cross‐track ion drift measurements. All available Swarm‐A and Swarm‐B 2 Hz data between November 2015 and July 2017 were used and the climatology of high‐latitude ion convection was constructed and examined. Results were compared to corresponding climatology obtained from the Weimer 2005 empirical convection electric field model under different interplanetary magnetic field and solar wind conditions in the northern and southern hemispheres, separately. The ion drift data sometimes exhibit large offsets at middle latitudes. However, following a recalibration of the drifts using a refinement of the offset removal, the Swarm cross‐track ion drift climatology agrees reasonably well statistically with the Weimer 2005 model, and properly responds to the changing geospace environment. The two results agree within about 200 m/s (root‐mean‐square deviation), however the correlations are higher for southward interplanetary magnetic field and in the northern hemisphere (rswarm‐A = 0.84, rswarm‐B = 0.77), for which the corresponding magnitudes of Swarm‐A and Swarm‐B drifts are ~14% and ~33% larger than the model estimates, respectively. The convection patterns seen in the revised Swarm horizontal cross‐track drift velocities are more structured than those obtained using the model, but overall no significant systematic errors are present.

Steve: The Optical Signature of Intense Subauroral Ion Drifts

“…The measurements from the satellites are well suited for the study of ionospheric subauroral phenomena. While a direct intersatellite comparison has not been done for the Swarm satellites, scientific publications using multiple Swarm satellites (Archer et al, 2015;Goodwin et al, 2015;Spicher et al, 2015) as well as validation studies (Lomidze et al, 2017(Lomidze et al, , 2019 all show the Swarm satellites to behave similarly to one another. The Swarm satellites measure electric and magnetic fields, as well as electron density and temperature; see Jørgensen et al (2008) and Knudsen et al (2017) for more information on the Swarm instrument package.…”

“…In this study we present measurements from all three Swarm satellites, which implies that the satellites are all calibrated to one another. While a direct intersatellite comparison has not been done for the Swarm satellites, scientific publications using multiple Swarm satellites (Archer et al, 2015;Goodwin et al, 2015;Spicher et al, 2015) as well as validation studies (Lomidze et al, 2017(Lomidze et al, , 2019 all show the Swarm satellites to behave similarly to one another.…”

The High‐Latitude Trough in the Southern Hemisphere Observed by Swarm‐A Satellite

“…The entire cross‐track ion drift data (Viy, in the horizontal direction perpendicular to the satellite orbit) from November 2015 to December 2017 are used. In order to get more usable ion drift data, the recalibration of data was carried out by setting the velocity to zero at midlatitudes (−45° magnetic latitude) in a similar way as described by Lomidze et al (). Lomidze et al () found that the recalibration cross‐track ion drift climatology agrees reasonably well in statistical sense with the Weimer () model.…”

“…In order to get more usable ion drift data, the recalibration of data was carried out by setting the velocity to zero at midlatitudes (−45° magnetic latitude) in a similar way as described by Lomidze et al (). Lomidze et al () found that the recalibration cross‐track ion drift climatology agrees reasonably well in statistical sense with the Weimer () model. In this study, we primarily focus on the influence of large‐scale FACs on the high‐latitude trough.…”

Testing the Electrodynamic Method to Derive Height-Integrated Ionospheric Conductances

“…We use an updated electric potential model by Edwards (2019), which supplements the database from the Dynamics Explorer-2 spacecraft that was used by Weimer (2005b) with a substantially larger number of measurements from the Swarm spacecraft (Lomidze et al, 2019). Previous models had derived the least-error fit of the model coefficients from electric potentials that were obtained by integrating the measured electric field values along the satellite's path; the latest version fit the coefficients https://doi.org/10.5194/angeo-2020-60 Preprint.…”