123 research outputs found
CIRENE Air-Sea Interactions in the Seychelles-Chagos Thermocline Ridge Region
A field experiment in the southwestern Indian Ocean provides new insights into ocean-atmosphere interactions in a key climatic region
Cirene : air-sea iInteractions in the Seychelles-Chagos thermocline ridge region
Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 90 (2009): 1337-1350, doi:10.1175/2008BAMS2499.1.The VascoâCirene program ex-plores how strong airâsea inter-actions promoted by the shallow thermocline and high sea surface temperature in the SeychellesâChagos thermocline ridge results in marked variability at synoptic, intraseasonal, and interannual time scales. The Cirene oceano-graphic cruise collected oceanic, atmospheric, and airâsea flux observations in this region in Jan-uaryâFebruary 2007. The contem-poraneous Vasco field experiment complemented these measure-ments with balloon deployments from the Seychelles. Cirene also contributed to the development of the Indian Ocean observing system via deployment of a moor-ing and 12 Argo profilers.
Unusual conditions prevailed in the Indian Ocean during Janu-ary and February 2007, following the Indian Ocean dipole climate anomaly of late 2006. Cirene measurements show that the SeychellesâChagos thermocline ridge had higher-than-usual heat content with subsurface anomalies up to 7°C. The ocean surface was warmer and fresher than average, and unusual eastward currents prevailed down to 800 m. These anomalous conditions had a major impact on tuna fishing in early 2007. Our dataset also sampled the genesis and maturation of Tropical Cyclone Dora, including high surface temperatures and a strong diurnal cycle before the cyclone, followed by a 1.5°C cool-ing over 10 days. Balloonborne instruments sampled the surface and boundary layer dynamics of Dora. We observed small-scale structures like dry-air layers in the atmosphere and diurnal warm layers in the near-surface ocean. The Cirene data will quantify the impact of these finescale features on the upper-ocean heat budget and atmospheric deep convection.CNES funded the Vasco part of the experiment; INSU
funded the Cirene part. R/V SuroĂźt is an Ifremer ship. The
contributions from ODU, WHOI, and FOI (Sweden) are
supported by the National Science Foundation under Grant
Number 0525657. The participation of the University of
Miami group was funded though NASA (NNG04HZ33C).
PMEL participation was supported through NOAAâs Office
of Climate Observation
EURECâŽA
The science guiding the EURECâŽA campaign and its measurements is presented. EURECâŽA comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic â eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EURECâŽA marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200âkm) and larger (500âkm) scales, roughly 400âh of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10â000 profiles), lower atmosphere (continuous profiling), and along the airâsea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EURECâŽA explored â from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation â are presented along with an overview of EURECâŽA's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement
EURECâŽA
The science guiding the EURECâŽA campaign and its measurements is presented. EURECâŽA comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic â eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EURECâŽA marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200âkm) and larger (500âkm) scales, roughly 400âh of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10â000 profiles), lower atmosphere (continuous profiling), and along the airâsea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EURECâŽA explored â from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation â are presented along with an overview of EURECâŽA's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement
Characterization of turbulence from a fine-scale parameterization and microstructure measurements in the Mediterranean Sea during the BOUM experiment
One of the main purposes of the BOUM experiment was to find evidence of the possible impact of submesoscale dynamics on biogeochemical cycles. To this aim physical as well as biogeochemical data were collected along a zonal transect through the western and eastern basins of the Mediterranean sea. Along this transect 3 day fixed point stations were performed within anticyclonic eddies during which microstructure measurements of the temperature gradient were collected over the top 100m of the water column. We focus here on the characterization of turbulent mixing
Ondes internes générées par le forçage atmosphérique dans l'océan indien subtropical (modélisation et mesures in situ)
Le déferlement des ondes internes est un des principaux mécanismes de mélange turbulent dans l océan et joue un rÎle clé sur la dynamique à plus grande échelle. L objectif de ce travail était de proposer une amélioration de la représentation du mélange turbulent dans les modÚles de circulation générale.La premiÚre partie porte sur l'analyse des mesures in situ de la campagne CIRENE dans l'océan Indien subtropical. Le passage d'un cyclone a conduit à la génération d'une onde de fréquence proche-inertielle dont nous avons pu suivre la propagation en profondeur.La seconde partie est consacrée à l'analyse des simulations forcées et couplées du modÚle NEMO. Dans tous les cas, on observe la génération d'ondes internes dans la bande de fréquence proche-inertielle suite à des coups de vent, cependant leur propagation est limitée en profondeur. Cette atténuation est attribuée à une trop forte valeur de la dissipation déterminée par le schéma TKE. Une paramétrisation spécifique déduite de paramétrisations fine-échelle est proposée.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF
Mixing in weakly turbulent stably stratified flows
We analyse mixing in three weakly turbulent stably stratified flows, namely low amplitude breaking internal gravity waves, stably stratified homogeneous decaying turbulence and a stably stratified unstable shear layer. We use the method proposed by Winter et al. [J. Fluid Mech. 289 (1995) 115], which provides an exact expression of the diffusive flux of density responsible for mixing. When the three flows have stabilized and organized into quasi-horizontal layers, we show that the diffusion coefficient behaves linearly as a function of a dynamical parameter that characterizes the largest scales of the flow (a Froude number squared or the inverse of a Richardson number) and we provide a simple expression of this linear law
Processus de mélange turbulent au niveau de la dorsale Médio-Atlantique
Dans l océan, le mélange turbulent, bien qu ayant lieu à petite échelle, a un impact important sur la circulation thermohaline et le transport de chaleur. Le mélange turbulent le plus intense est observé dans les régions de topographie accidentée, telles que les dorsales océaniques. La thÚse porte sur la caractérisation des différents processus dynamiques responsables du mélange turbulent au niveau du site Lucky Strike, situé à 37N sur la dorsale Médio Atlantique. Le site se compose de deux bassins semi-isolés du reste de l'océan et localisés au sein de la vallée de la dorsale. Ces deux bassins sont reliés entre eux par un passage au milieu duquel se trouve un volcan sous marin, créant ainsi deux passages étroits à ses cÎtés. Différents processus dynamiques à l'origine du mélange turbulent ont été identifiés à partir de mesures in situ. Au niveau du seuil, les données de deux mouillages montrent que la dynamique en profondeur est caractérisée par un écoulement basse fréquence fortement cisaillé, ainsi que des épisodes intermittents de marée interne semi-diurne. Les mesures récoltées dans les 500 premiers mÚtres quant à elles mettent en évidence les instabilités d'un champ d'ondes internes. La premiÚre étape afin de déterminer la contribution de ces processus dynamiques au mélange turbulent a été de valider les paramétrisations fine-échelle du mélange turbulent à partir de mesures microstructure. Ces paramétrisations ont ensuite permis d'estimer la variabilité du mélange turbulent à partir des données de mouillage. Les estimations de la dissipation turbulente sont de l'ordre de 10^-8 W/kg, soit deux ordres de grandeur plus élevées que les valeurs rencontrées dans l'océan intérieur.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF
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