At midlatitudes in the ionosphere, just below the auroral region, narrow channels of strong westward flow have been observed. These flows, known as subauroral polarization streams (SAPS), are driven by pressure gradients in near-Earth space and are a manifestation of the coupling between the upper atmosphere and the magnetosphere. To better understand these flows, Clausen et al. measured the flow velocities inside SAPS using the new midlatitude chain of Super Dual Auroral Radar Network (SuperDARN) instruments. The observations, which lasted for 3 hours and covered the entire North American continent, are the first large-scale simultaneous observations of the velocity structure of SAPS.