242 research outputs found
Interactions between the Somali Current eddies during the summer monsoon: insights from a numerical study
International audienceThree hindcast simulations of the global ocean circulation differing by resolution (1/4 or 1/12°) or parametrization or atmospheric forcing are used to describe the interactions between the large anticyclonic eddies generated by the Somali Current system during the Southwest Monsoon. The present investigation of the Somalian coherent eddy structures allows us to identify the origin and the subsequent development of the cyclones flanked upon the Great Whirl (GW) previously identified by Beal and Dono-hue (2013) in satellite observations and to establish that similar cyclones are also flanked upon the Southern Gyre (SG). These cyclones are identified as potential actors in mixing water masses within the large eddies and offshore the coast of Somalia. All three simulations bring to light that during the period when the Southwest Monsoon is well established, the SG moves northward along the Somali coast and encounters the GW. The interaction between the SG and the GW is a collision without merging, in a way that has not been described in observations up to now. During the collision the GW is pushed to the east of Socotra Island, sheds several smaller patches of anticyclonic vorticity, and often reforms into the Socotra Eddy, thus proposing a formation mechanism for that eddy. During this process the GW gives up its place to the SG. This process is robust throughout the three simulations
Ro-vibrational analysis of the XUV photodissociation of HeH ions
We investigate the dynamics of the photodissociation of the hydrohelium
cation HeH by XUV radiation with the aim to establish a detailed comparison
with a recent experimental work carried out at the FLASH free electron laser
using both vibrationally hot and cold ions. As shown in previous theoretical
works, the comparison is hindered by the fact that the experimental
ro-vibrational distribution of the ions is unknown. We determine this
distribution using a dissociative charge transfer set-up and the same source
conditions as in the FLASH experiment. Using a non-adiabatic time-dependent
wave packet method, we calculate the partial photodissociation cross sections
for the coupled electronic states of HeH. We find a good agreement
with the experiment for the total cross section into the He + H
dissociative channel. By performing an adiabatic calculation involving the
states, we then show that the experimental observation of the importance
of the electronic states with cannot be well explained theoretically,
especially for cold () ions. We also calculate the relative contributions
to the cross section of the and states. The agreement with the
experiment is excellent for the He + H channel, but only qualitative for
the He + H channel. We discuss the factors that could explain the remaining
discrepancies between theory and experiment.Comment: 10 pages, 8 figure
Etude préliminaire des relations entre le complexe majeur d'histocompatibilité (SLA) et des caractères de production chez le porc
Improved Phylogenomic Taxon Sampling Noticeably Affects Nonbilaterian Relationships
Despite expanding data sets and advances in phylogenomic methods, deep-level metazoan relationships remain highly controversial. Recent phylogenomic analyses depart from classical concepts in recovering ctenophores as the earliest branching metazoan taxon and propose a sister-group relationship between sponges and cnidarians (e.g., Dunn CW, Hejnol A, Matus DQ, et al. (18 co-authors). 2008. Broad phylogenomic sampling improves resolution of the animal tree of life. Nature 452:745–749). Here, we argue that these results are artifacts stemming from insufficient taxon sampling and long-branch attraction (LBA). By increasing taxon sampling from previously unsampled nonbilaterians and using an identical gene set to that reported by Dunn et al., we recover monophyletic Porifera as the sister group to all other Metazoa. This suggests that the basal position of the fast-evolving Ctenophora proposed by Dunn et al. was due to LBA and that broad taxon sampling is of fundamental importance to metazoan phylogenomic analyses. Additionally, saturation in the Dunn et al. character set is comparatively high, possibly contributing to the poor support for some nonbilaterian nodes
The Oceanic Variability Spectrum and Transport Trends
Oceanic meridional transports evaluated over the width of the Pacific Ocean from altimetric observations become incoherent surprisingly rapidly with meridional separation. Even
with 15 years of data, surface slopes show no significant coherence beyond 5◦ of latitude separation at any frequency. An analysis of the frequency/zonal-wavenumber spectral density
shows a broad continuum of motions at all time and space scales, with a significant excess of energy along a “non-dispersive” line extending between the simple barotropic and first baroclinic mode Rossby waves. It is speculated that much of that excess energy lies with coupled barotropic and first mode Rossby waves. The statistical significance of apparent oceanic transport trends depends upon the existence of a reliable frequency/wavenumber spectrum and for which only a few observational elements now exist.Jet Propulsion Laboratory (U.S.).United States. National Aeronautics and Space Administration (Jason-1 program)National Oceanographic Partnership Program (U.S.
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