Concordiasi is a multidisciplinary effort jointly operated by France and the United States to study the lower stratosphere and troposphere above Antarctica as well as the land surface of the Antarctic continent. Concordiasi field experiments took place in austral springs 2008, 2009, and 2010, including surface measurements and radiosoundings at the Concordia Antarctica station at Dome C and radio-soundings at the Dumont d'Urville and Rothera sites on Antarctica. In 2010 an innovative constellation of balloons provided a unique set of measurements covering both volume and time. The balloons—13 driftsondes and six balloons with tethered gondolas dedicated to middle atmosphere measurements— drifted for several months on isopycnic surfaces in the lowermost stratosphere around 18 km, circling over Antarctica in the winter vortex. The balloon flotilla formed a regional observatory of the atmo-sphere, which provided in situ measurements inside