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Balloons are one of the key observing platforms for the atmosphere. Radiosounding is the most commonly used technique and provides over a thousand vertical profiles worldwide every day. These data represent an essential cornerstone of data assimilation for numerical weather prediction systems. Although less common (but 25 equally interesting for the in-situ investigation of the atmosphere), drifting boundary layer pressurized balloons (BLPBs) offer rare observational skills. These balloons collect meteorological and/or chemical measurements at isopycnal height as they drift in a quasi Lagrangian way. The BLPB system presented in this paper was developed by the French space agency (CNES) and has been used in field 30 experiments focusing on precipitation in Africa (AMMA) and the Mediterranean (HyMeX) as well as on air pollution in India (INDOEX) and the Mediterranean (TraQa, ChArMeX). One important advantage of the BLPBs is their capability to explore the lowest layers of the atmosphere above the oceans, areas that remain difficult to access. BLPB had a leading role in a complex adaptive observation system for the 35 forecast of severe precipitation events. These balloons collected data in the marine environment of convective systems, which were assimilated in real time to improve the knowledge of the state of the atmosphere in the numerical prediction models of Météo-France. 3 Capsule:Low atmosphere, constant volume balloons offer unique observing capabilities, such as Lagrangian sampling of air masses and data collection for weather prediction.These aspects are illustrated through field campaigns using CNES balloons. 45 4

International audienceConstellations of driftsonde systems— gondolas floating in the stratosphere and able to release dropsondes upon command— have so far been used in three major field experiments from 2006 through 2010. With them, high-quality, high-resolution, in situ atmospheric profiles were made over extended periods in regions that are otherwise very difficult to observe. The measurements have unique value for verifying and evaluating numerical weather prediction models and global data assimilation systems; they can be a valuable resource to validate data from remote sensing instruments, especially on satellites, but also airborne or ground-based remote sensors. These applications for models and remote sensors result in a powerful combination for improving data assimilation systems. Driftsondes also can support process studies in otherwise difficult locations—for example, to study factors that control the development or decay of a tropical disturbance, or to investigate the lower boundary layer over the interior Antarctic continent. The driftsonde system is now a mature and robust observing system that can be combined with flight-level data to conduct multidisciplinary research at heights well above that reached by current research aircraft. In this article we describe the development and capabilities of the driftsonde system, the exemplary science resulting from its use to date, and some future applications

Aeroclipper balloons, designed for taking measurements at the air-sea interface, can withstand extreme conditions encountered when they are drawn into tropical cyclones and then follow the eye trajectory. The Aeroclipper (Fig. 1) is a new balloon device designed to perform relatively long flights (of up to 30 days) in the surface layer (under 50 m) over remote ocean regions. Up to now, most long-lasting balloon measurements in the marine boundary layer have been made using superpressure balloons. These superpressure balloons have a constant volume and are thus supposed to fly at a level of constant density. Superpressure balloons in the boundary layer were first developed to probe local dynamical properties along Lagrangian trajectories. Early experiments used a manually operated radar to follow aluminized tetrahedral balloons (or tetroons) for a few hours (Angell and Pack 1960). These tetroons were found to be suitable Lagrangian tracers at a constant level. They were progressively improved (by adding, e.g., a radar transponder) and contributed to new results on turbulence, diffusion, and transport properties, in particular over urban areas (see Businger et al. 1996 for a review). Superpressure balloons of various shapes are still used in local field experiments. These balloons have a life expectancy of a few hours and require a local receiver system. In order to study large-scale flows in the marine boundary layer over remote regions, long-lasting balloons tracked by satellite are required. For the VASCO prototypes, there were two transmission gondolas, one dedicated to science telemetry (using either Argos for Aeroclippers 1,2,3, and 7, or Iridium for the others) and a security transmission gondola providing a redundancy of the position as well as software for automatic balloon separation in forbidden areas (around the island and continental regions). The length of the guide rope is 50 m between the ocean gondola and the security transmission gondola.