Non‐Geophysical Interhemispheric Asymmetries in Large Magnetic Field Residuals Between Swarm Observations and Earth Magnetic Field Models During Moderate to Quiet Geomagnetic Conditions

Abstract

AbstractWe present a statistical study of large magnetic field vector residuals between Swarm observations and the 13th generation International Geomagnetic Reference Field (IGRF‐13) model under quiet to moderate geomagnetic conditions. Since the vast majority of data are taken during these conditions, statistics of these large residuals are important for satellite operation when using IGRF‐13 as reference, as well as for magnetosphere‐ionosphere‐thermosphere studies. Residuals with magnitude of vector differences between observations and model estimations larger than 300 nT under Dst > −50 nT are studied from 2014 to 2020. All large residuals appear in the high‐latitude auroral zone region peaking around 70° (−70°) magnetic latitude (MLAT) in the northern hemisphere (southern hemisphere) with also a secondary occurrence peak just below 80° (−80°) MLAT. However, the two hemispheres show clear asymmetries in the magnetic longitude and magnetic local time distribution where both hemispheres show high concentration of large residuals around the geographic poles. Since polar satellite's orbits give rise to highly biased number of observations around the geographic poles, it results in a decrease in occurrence rate with respect to the total number of measurements. We suggest that the asymmetries of large residuals in the two hemispheres around the geographic pole are not geophysical, but due to satellite orbit bias around the geographic poles and difference between IGRF and observations due to model error and geophysical processes not included in the model. Identifying these biases is helpful to better separate out geophysical electric current signatures from non‐geophysical ones.