[1] The cryogenic frost point hygrometer (CFH), currently built at the University of Colorado, is a new balloon borne hygrometer, which is capable of continuously measuring water vapor between the surface and the middle stratosphere. The design is loosely based on the old NOAA/CMDL frost point hygrometer, with improved accuracy and a number of significant new features that overcome some limitations of the older instrument. The measurement uncertainty of the new instrument depends on altitude and ranges between less than 4% in the tropical lower troposphere to no more than 10% in the middle stratosphere at 28 km. In the tropopause region the uncertainty is less than 9%. This instrument is used routinely at several sites for validation of satellite measurements and process studies in the upper troposphere and lower stratosphere region. It has proved to be particularly well suited for dehydration observations in the tropical upper troposphere, because the effects of cloud contamination have been significantly reduced. Results of this instrument are compared with the old NOAA/CMDL hygrometer, the Russian Fluorescent Lyman Alpha Stratospheric Hygrometer, the Vaisala RS92, the AURA/MLS satellite instrument, a cloud lidar, the NOAA/CSD frost point hygrometer and the Harvard Lyman-alpha hygrometer, both of the later instruments flown on board the NASA WB-57F high-altitude research aircraft. These comparisons demonstrate the level of accuracy of tropospheric and stratospheric water vapor measurements made by this instrument and point to areas where more research and development are needed.

Ocean tracers such as carbon dioxide, nutrients, plankton, and oil advect, diffuse, and react primarily in the oceanic mixed layer where air‐sea gas exchange occurs and light is plentiful for photosynthesis. There can be substantial heterogeneity in the spatial distributions of these tracers due to turbulent stirring, particularly in the submesoscale range where partly geostrophic fronts and eddies and small‐scale three‐dimensional turbulence are simultaneously active. In this study, a large eddy simulation spanning horizontal scales from 20 km down to 5 m is used to examine the effects of multiscale turbulent mixing on nonreactive passive ocean tracers from interior and sea‐surface sources. The simulation includes the effects of both wave‐driven Langmuir turbulence and submesoscale eddies, and tracers with different initial and boundary conditions are examined in order to understand the respective impacts of small‐scale and submesoscale motions on tracer transport. Tracer properties are characterized using spatial fields and statistics, multiscale fluxes, and spectra, and the results detail how tracer mixing depends on air‐sea tracer flux rate, tracer release depth, and flow regime. Although vertical fluxes of buoyancy by submesoscale eddies compete with mixing by Langmuir turbulence, vertical fluxes of tracers are often dominated by Langmuir turbulence, particularly for tracers that are released near the mixed‐layer base or that dissolve rapidly through the surface, even in regions with pronounced submesoscale activity. Early in the evolution of some tracers, negative eddy diffusivities occur co‐located with regions of negative potential vorticity, suggesting that symmetric instabilities or other submesoscale phenomenon may act to oppose turbulent mixing.

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.

We use idealized large-eddy simulations (LES) and a simple analytical theory to study the influence of submesoscales on the concentration and export of sinking particles from the mixed layer. We find that restratification of the mixed layer following the development of submesoscales reduces the rate of vertical mixing which, in turn, enhances the export rate associated with gravitational settling. For a neutral tracer initially confined to the mixed layer, subinertial (submesoscale) motions enhance the downward tracer flux, consistent with previous studies. However, the sign of the advective flux associated with the concentration of sinking particles reverses, indicating reentrainment into the mixed layer. A new theory is developed to model the gravitational settling flux when the particle concentration is nonuniform. The theory broadly agrees with the LES results and allows us to extend the analysis to a wider range of parameters.