The first science flight of the balloon-borne Sunrise telescope took place in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset Island in northern Canada. We describe the scientific aims and mission concept of the project and give an overview and a description of the various hardware components: the 1-m main telescope with its postfocus science instruments (the UV filter imager SuFI and the imaging vector magnetograph IMaX) and support instruments (image stabilizing and light distribution system ISLiD and correlating wavefront sensor CWS), the optomechanical support structure and the instrument mounting concept, the gondola structure and the power, pointing, and telemetry systems, and the general electronics architecture. We also explain the optimization of the structural and thermal design of the complete payload. The preparations for the science flight are described, including AIV and ground calibration of the instruments. The course of events during the science flight is outlined, up to the recovery activities. Finally, the in-flight performance of the instrumentation is discussed.

Abstract. We describe CO 2 concentration measurement systems based on relatively inexpensive single-cell nondispersive infrared CO 2 sensors. The systems utilize signal averaging to obtain precision (1-σ in 100 s) of 0.1 parts per million dry air mole fraction (ppm), frequent calibrations and sample drying in order to achieve state-of-the-art compatibility, and can run autonomously for months at a time. Laboratory tests indicate compatibility among four to six systems to be ±0.1 ppm (1-σ ), and field measurements of known reference-gases yield median errors of 0.01 to 0.17 ppm with 1-σ variance of ±0.1 to 0.2 ppm. From May to August 2007, a system co-located with a NOAA-ESRL dual-cell NDIR system at the WLEF tall tower in Wisconsin measured daytime-only daily averages of CO 2 that differ by 0.26 ± 0.15 ppm (median ± 1 σ ), and from August 2005 to April 2011 a system co-located with weekly NOAA-ESRL network flask collection at Niwot Ridge, Colorado measured coincident CO 2 concentrations that differed by −0.06 ± 0.30 ppm (n = 585). Data from these systems are now supporting a wide range of analyses and this approach may be applicable in future studies where accuracy and initial cost of the sensors are priorities.

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A s the primary conduit for CO 2 and heat exchange between the atmosphere and the deep ocean, the Southern Ocean is an important part of the climate system. Approximately 40% of the ocean's inventory of anthropogenic carbon entered through the air-sea interface south of 40°S (Khatiwala et al. 2009), and the region will continue to serve as an important carbon sink into the future (Ito et al. 2015). Despite its importance, the processes controlling air-sea gas exchange in the Southern Ocean are poorly represented by models. This was highlighted in a recent comparison of models from phase 5 of the Coupled Model Intercomparison Project (CMIP5), wherein the simulated seasonal cycles of air-sea CO 2 exchange with the Southern Ocean were widely divergent and in poor agreement with observational estimates (Anav et al. 2013;Jiang et al. 2014), suggesting possible model biases in the timing, spatial A recent Southern Ocean airborne campaign collected continuous, discrete, and remote sensing measurements to investigate biogeochemical and physical processes driving air-sea exchange of CO 2 , O 2 , and reactive biogenic gases.

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