Progress with the Prime Focus Spectrograph for the Subaru Telescope: a massively multiplexed optical and near-infrared fiber spectrograph

The Prime Focus Spectrograph (PFS) is an optical/near-infrared multi-fiber spectrograph with 2394 science fibers, which are distributed in 1.3 degree diameter field of view at Subaru 8.2-meter telescope. The simultaneous wide wavelength coverage from 0.38 um to 1.26 um, with the resolving power of 3000, strengthens its ability to target three main survey programs: cosmology, Galactic archaeology, and galaxy/AGN evolution. A medium resolution mode with resolving power of 5000 for 0.71 um to 0.89 um also will be available by simply exchanging dispersers. PFS takes the role for the spectroscopic part of the Subaru Measurement of Images and Redshifts project, while Hyper Suprime-Cam works on the imaging part. To transform the telescope plus WFC focal ratio, a 3-mm thick broad-band coated glass-molded microlens is glued to each fiber tip. A higher transmission fiber is selected for the longest part of cable system, while one with a better FRD performance is selected for the fiber-positioner and fiber-slit components, given the more frequent fiber movements and tightly curved structure. Each Fiber positioner consists of two stages of piezo-electric rotary motors. Its engineering model has been produced and tested. Fiber positioning will be performed iteratively by taking an image of artificially back-illuminated fibers with the Metrology camera located in the Cassegrain container. The camera is carefully designed so that fiber position measurements are unaffected by small amounts of high special-frequency inaccuracies in WFC lens surface shapes. Target light carried through the fiber system reaches one of four identical fast-Schmidt spectrograph modules, each with three arms. Prototype VPH gratings have been optically tested. CCD production is complete, with standard fully-depleted CCDs for red arms and more-challenging thinner fully-depleted CCDs with blue-optimized coating for blue arms.Comment: 14 pages, 12 figures, submitted to "Ground-based and Airborne Instrumentation for Astronomy V, Suzanne K. Ramsay, Ian S. McLean, Hideki Takami, Editors, Proc. SPIE 9147 (2014)

Couche mélangée océanique et bilan thermohalin de surface dans l'Océan Indien Nord

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology

A new 2° resolution global climatology of the mixed layer depth (MLD) based on individual profiles is constructed. Previous global climatologies have been based on temperature or density-gridded climatologies. The criterion selected is a threshold value of temperature or density from a near-surface value at 10 m depth (?T = 0.2°C or ?? = 0.03 kg m?3). A validation of the temperature criterion on moored time series data shows that the method is successful at following the base of the mixed layer. In particular, the first spring restratification is better captured than with a more commonly used larger criteria. In addition, we show that for a given 0.2°C criterion, the MLD estimated from averaged profiles results in a shallow bias of 25% compared to the MLD estimated from individual profiles. A new global seasonal estimation of barrier layer thickness is also provided. An interesting result is the prevalence in mid- and high-latitude winter hemispheres of vertically density-compensated layers, creating an isopycnal but not mixed layer. Consequently, we propose an optimal estimate of MLD based on both temperature and density data. An independent validation of the maximum annual MLD with oxygen data shows that this oxygen estimate may be biased in regions of Ekman pumping or strong biological activity. Significant differences are shown compared to previous climatologies. The timing of the seasonal cycle of the mixed layer is shifted earlier in the year, and the maximum MLD captures finer structures and is shallower. These results are discussed in light of the different approaches and the choice of criterion

Toward global maps of internal tide energy sinks

International audienceInternal tides power much of the observed small-scale turbulence in the ocean interior. To represent mixing induced by this turbulence in ocean climate models, the cascade of internal tide energy to dissipation scales must be understood and mapped. Here, we present a framework for estimating the geography of internal tide energy sinks. The mapping relies on the following ingredients: (i) a global observational climatology of stratification; (ii) maps of the generation of M2, S2 and K1 internal tides decomposed into vertical normal modes; (iii) simplified representations of the dissipation of low-mode internal tides due to wave-wave interactions, scattering by small-scale topography, interaction with critical slopes and shoaling; (iv) Lagrangian tracking of low-mode energy beams through observed stratification, including refraction and reflection. We thus obtain a global map of the column-integrated energy dissipation for each of the four considered dissipative processes, each of the three tidal constituents and each of the first five modes. Modes ≥6 are inferred to dissipate within the local water column at the employed half-degree horizontal resolution. Combining all processes, modes and constituents, we construct a map of the total internal tide energy dissipation, which compares well with observational inferences of internal wave energy dissipation. This result suggests that tides largely shape observed spatial contrasts of dissipation, and that the framework has potential in improving understanding and modelling of ocean mixing. However, sensitivity to poorly constrained parameters and simplifying assumptions entering the parameterized energy sinks calls for additional investigation. The attenuation of low-mode internal tides by wave-wave interactions needs particular attention

Partial wing transparency works better when disrupting wing edges: evidence from a field experiment

International audienc

Variability and remote controls of the warm‐water halo and Taylor Cap at Maud Rise

The region of Maud Rise, a seamount in the Weddell Sea, is known for the occurrence of irregular polynya openings during the winter months. Hydrographic observations have shown the presence of a warmer water mass below the mixed layer along the seamount's flanks, commonly termed the warm-water Halo, surrounding a colder region above the rise, the Taylor Cap. Here we use two observational data sets, an eddy-permitting reanalysis product and regional high-resolution simulations, to investigate the interannual variability of the Halo and Taylor Cap for the period 2007–2022. Observations include novel hydrographic profiles obtained in the Maud Rise area in January 2022, during the first SO-CHIC cruise. It is demonstrated that the temperature of deep waters around Maud Rise exhibits strong interannual variability within the Halo and Taylor Cap, occasionally to such an extent that the two features become indistinguishable. A warming of deep waters by as much as 0.8°C is observed in the Taylor Cap during the years preceding the opening of a polynya in 2016 and 2017, starting in 2011. By analyzing regional simulations, we show that most of the observed variability in the Halo is forced remotely by advection of deep waters from the Weddell Gyre into the region surrounding Maud Rise. Our highest-resolution simulation indicates that mesoscale eddies subsequently transfer the properties of the Halo's deep waters onto the Taylor Cap. The eddies responsible for such transfer originate in an abrupt retroflection along the inner flank of the Halo

Global maps of internal tide generation and dissipation

The dataset consists of global two-dimensional maps of internal tide energy sources and sinks, at half-degree horizontal resolution. Estimated energy sources are provided for the three most energetic tidal constituents: M2, S2 and K1. They are decomposed into vertical normal modes. Units are Watts per square meter. Estimated energy sinks are provided for each of M2, S2 and K1 and for &#39;All constituents&#39;. &#39;All constituents&#39; is an extrapolation to the eight most energetic tidal constituents, obtained as a weighted sum of M2, S2 and K1 fields. Energy sinks are depth-integrated and decomposed into five process contributions: (i) local dissipation of high modes; (ii) dissipation of low modes via wave-wave interactions; (iii) dissipation of low modes via scattering by abyssal hills; (iv) dissipation of low modes via critical reflection; (v) dissipation of low modes via shoaling. Units are Watts per square meter. Methods and documentation can be found in the following publication: de Lavergne, C., Falahat, S., Madec, G., Roquet, F., Nycander, J., Vic, C. Toward global maps of internal tide energy sinks. Ocean Modelling, 137, 52-75 (2019). doi:10.1016/j.ocemod.2019.03.010. Provided maps of energy sinks correspond to the reference (REF) experiment described in the article.</span

Global estimates of internal tide generation rates at 1/30&ordm; resolution

The dataset contains global estimates of barotropic-to-baroclinic tidal energy conversion at 1/30-degree resolution. Three types of estimates are available: 1. Non-modal conversion rates calculated by Falahat et al. (2014) following the method of Nycander (2005). A map for each of the eight most energetic tidal constituents (M2, S2, K1, O1, N2, K2, P1, Q1) is provided. 2. Mode-by-mode conversion rates calculated by Falahat et al. (2014). A map for each of the three most energetic tidal constituents (M2, S2, K1) and each of vertical normal modes 1, 2, 3, 4, 5 and 6-10 is provided. 3. Mode-by-mode conversion rates calculated by Falahat et al. (2014), to which an ad hoc correction to eliminate negative conversion rates has been applied (following de Lavergne et al., 2019). The correction preserves basin-integrated, depth-dependent conversion rates. A map for each of the three most energetic tidal constituents (M2, S2, K1) and each of vertical normal modes 1, 2, 3, 4, 5 and 6-10 is provided. All maps were computed using the WOCE global climatology of stratification, the ETOPO2v2 bathymetry product and the TXO6.2 atlas of barotropic tidal velocities. Detailed methods and documentation can be found in the following publications: Nycander, J. Generation of internal waves in the deep ocean by tides. Journal of Geophysical Research 110, C10028 (2005). doi:10.1029/2004JC002487 Falahat, S., Nycander, J., Roquet, F., Moundheur, Z. Global calculation of tidal energy conversion into vertical normal modes. Journal of Physical Oceanography 44, 3225-3244 (2014). doi:10.1175/JPO-D-14-0002.1 de Lavergne, C., Falahat, S., Madec, G., Roquet, F., Nycander, J., Vic, C. Toward global maps of internal tide energy sinks. Ocean Modelling,137, 52-75 (2019). doi:10.1016/j.ocemod.2019.03.010.</span