Maps showing the magnitude of the horizontal magnetospheric field at satellite altitude. Each map represents a monthly averaged field based on geomagnetically quiet periods over the 10-year Swarm mission dataset. The panels display averages for March (upper left) and June (upper right), September (lower left) and December (lower right). The bottom panel shows the average monthly amplitude of $⟨q_1^0⟩$ for all data over 10 years (blue) and for selected quiet time only (orange). Dashed grey vertical lines correspond to the times of the snapshots above. Solid grey vertical lines mark the equinoxes.