Day-To-Day Variability of the Neutral Wind Dynamo Observed by ICON: First Results From Conjugate Observations

First results are presented from the conjugate maneuvers performed by NASA's Ionospheric Connection Explorer (ICON) spacecraft. During each several-minute maneuver, ICON crosses the magnetic equator, measuring the plasma drift at the similar to 600-km apex of a magnetic field line and the neutral wind profiles (similar to 90-300 km altitude) along both ends of that field line. The analysis utilizes 149 pairs of maneuvers separated by similar to 24 hr but at nearly the same location and local time. Principal component regression reveals that 39 +/- 7% and 24 +/- 9% of the day-to-day variance in the daytime vertical and zonal drift, respectively, is attributable to conjugate neutral winds. The remaining variance is likely driven by external potentials from non-conjugate winds and geomagnetic activity (median Kp 2-). Zonal winds at 100-113 km and >120 km altitude are the primary drivers of conjugate vertical and zonal drift variance, respectively. These observations can test vertical-coupling mechanisms in whole-atmosphere models. Plain Language Summary The plasma that composes the ionosphere can change dramatically from one day to the next, exhibiting significant changes in its height and density which are not well predicted by models. This variability can have adverse impacts on satellite-based navigation and communication systems, limiting their performance and availability. One of the key parameters that controls daytime ionospheric conditions is the upward and downward motion of plasma above 200 km, which affects the lifetime of newly created plasma. The force that puts the plasma in motion is electromotive, generated by the motion of the atmosphere (i.e., the wind) around 100-150 km that pushes charged particles across magnetic field lines. NASA's Ionospheric Connection Explorer is the first mission to directly observe these electrical generators, one at each "footpoint" of the arched magnetic field lines that thread the ionosphere and generator region. The results show that just under half of the day-to-day changes in ionospheric motion can be explained by this local generator mechanism. The major controller is the east-west winds, with north-south winds having only a minor influence on this mechanism.