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Lallement R.,University Paris Diderot | Vergely J.-L.,ACRI ST | Valette B.,CNRS Institute of Earth Sciences | Puspitarini L.,University Paris Diderot | And 2 more authors.
Astronomy and Astrophysics | Year: 2014

Aims. Three-dimensional (3D) maps of the Galactic interstellar matter (ISM) are a potential tool of wide use, but accurate and detailed maps are still lacking. One of the ways to construct the maps is to invert individual distance-limited ISM measurements, a method we have applied here to measurements of stellar color excess in the optical. Methods. We assembled color excess data together with the associated parallax or photometric distances to constitute a catalog of â‰23 000 sightlines for stars within 2.5 kpc. The photometric data are taken from Strömgren catalogs, the Geneva photometric database, and the Geneva-Copenhagen survey. We also included extinctions derived towards open clusters. We applied an inversion method based on a regularized Bayesian approach to this color excess dataset, a method previously used for mapping at closer distances. Results. We show the dust spatial distribution resulting from the inversion by means of planar cuts through the differential opacity 3D distribution, and by means of 2D maps of the integrated opacity from the Sun up to various distances. The mapping assigns locations to the nearby dense clouds and represents their distribution at the spatial resolution that is allowed by the dataset properties, i.e. â‰10 pc close to the Sun and increasing to â‰100 pc beyond 1 kpc. Biases toward nearby and/or weakly extincted stars make this dataset particularly appropriate to mapping the local and neighboring cavities and to locating faint, extended nearby clouds, which are both goals that are difficult or impossible with other mapping methods. The new maps reveal a â‰1 kpc wide empty region in the third quadrant in the continuation of the so-called CMa tunnel of the Local Cavity, a cavity that we identify as the Superbubble GSH238+00+09 detected in radio emission maps and that is found to be bounded by the Orion and Vela clouds. The maps also show an extended narrower tunnel in the opposite direction (l ≠70) that also extends the Local Bubble further and together with it forms a conspicuous cavity bounded by the main Lup, Sco, Oph, Aql, Lac, Cep, and Tau clouds and OB associations. This chain of cavities and surrounding dense regions constitute the first computed representation of the well known Gould belt/Lindblad ring structures. Finally, almost all off-plane faint features that appear in 2D dust maps have a counterpart in the 3D maps, providing the dust distribution in nearby tenuous clouds. © 2014 ESO.


Bressac M.,ACRI ST | Bressac M.,French National Center for Scientific Research | Guieu C.,French National Center for Scientific Research
Global Biogeochemical Cycles | Year: 2013

Abiotic iron removal processes such as scavenging can significantly and rapidly modify iron distribution in the dissolved-colloidal-particulate continuum. Therefore, these processes could be considered, in addition to ligand complexation, as a major control on atmospheric iron dissolution in seawater. In this work, we investigated the seasonal abiotic processes occurring once dust deposited on surface seawater using a series of artificial seeding experiments (allowing us to take into consideration the settling of particles on a 1 m depth layer). Here, we demonstrate that atmospheric dissolved iron concentration ([DFe]) is driven by the processes governed by the dissolved organic matter (DOM) pool. Following artificial dust seeding, an order magnitude range increase in the [DFe] (12 - 181 nmol L-1) was observed depending on the season. Under high and fresh DOM conditions (spring and summer), the rapid formation of aggregates induced a negative feedback on the [DFe] through scavenging, while a fraction of the DFe was likely organically complexed. In contrast, in low-DOM surface waters (winter), aggregation was not observed, allowing a very large transient increase in [DFe] (181 nmol L-1) before being removed by adsorption onto settling particles. A key result of the findings is that depending on the age and quantity of DOM, the "lithogenic carbon pump" is likely a major pathway for organic carbon export. Modeling studies should therefore relate both atmospheric iron dissolution in seawater and the intensity of the subsequent biological response, to the age and quantity of DOM. Key Points Atmospheric iron dissolution is driven by the dissolved organic matter poolSeawater biogeochemical conditions are a key determinant of iron solubilityLithogenic carbon pump is likely a major pathway for organic carbon export. © 2013. American Geophysical Union. All Rights Reserved.


Combi M.R.,University of Michigan | Fougere N.,University of Michigan | Makinen J.T.T.,Finnish Meteorological Institute | Bertaux J.-L.,University of Versailles | And 2 more authors.
Astrophysical Journal Letters | Year: 2014

The Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyα camera on the SOlar and Heliospheric Observer (SOHO) satellite observed the hydrogen coma of comet C/2012 S1 (ISON) for most of the last month of its activity from 2013 October 24 to November 24, ending just 4 days before perihelion and its final disruption. The water production rate of the comet was determined from these observations. SOHO has been operating in a halo orbit around the Earth-Sun L1 Lagrange point since its launch in late 1995. Most water vapor produced by comets is ultimately photodissociated into two H atoms and one O atom producing a huge hydrogen coma that is routinely observed in the daily SWAN images in comets of sufficient brightness. Water production rates were calculated from 22 images over most of the last month of the pre-perihelion apparition. The water production rate increased very slowly on average from October 24.9 until November 12.9, staying between 1.8 and 3.4 × 1028 s -1, after which it increased dramatically, reaching 1.6 to 2 × 1030 s-1 from November 21.6 to 23.6. It was not detected after perihelion on December 3.7 when it should have been visible. We examine the active surface area necessary to explain the water production rate and its variation and are able to place constraints on the physical size of the original nucleus necessary to account for the large amount of activity from November 12.9 and until just before perihelion. © 2014. The American Astronomical Society. All rights reserved..


Combi M.R.,University of Michigan | Bertaux J.-L.,University of Versailles | Quemerais E.,University of Versailles | Ferron S.,ACRI st | Makinen J.T.T.,Finnish Meteorological Institute
Astrophysical Journal Letters | Year: 2011

Global water production rates were determined from the Lyα emission of hydrogen around comet 103P/Hartley 2, observed with the SWAN (Solar Wind Anisotropies) all-sky camera on the SOHO spacecraft from 2010 September 14 through December 12. This time period included the November 4 flyby by the EPOXI spacecraft. Water production was three times lower than during the 1997 apparition also measured by SWAN. In 2010, it increased by a factor of 2.5 within one day on September 30 with a similar corresponding drop between November 24 and 30. The total surface area of sublimating water within 20 days of perihelion was 0.5km2, about half of the mean cross section of the nucleus. Outside this period it was 0.2km2. The peak value was 90%, implying a significant water production by released nucleus icy fragments. © 2011. The American Astronomical Society. All rights reserved.


Maritorena S.,University of California at Santa Barbara | d'Andon O.H.F.,ACRI ST | Mangin A.,ACRI ST | Siegel D.A.,University of California at Santa Barbara
Remote Sensing of Environment | Year: 2010

The characteristics and benefits of ocean color merged data sets created using a semi-analytical model and the normalized water-leaving radiance observations from the SeaWiFS, MODIS-AQUA and MERIS ocean color missions are presented. Merged data products are coalesced from multiple mission observations into a single data product with better spatial and temporal coverage than the individual missions. Using the data from SeaWiFS, MODIS-AQUA and MERIS for the 2002-2009 time period, the average daily coverage of a merged product is ∼ 25% of the world ocean which is nearly twice that of any single mission's observations. The frequency at which a particular area is sampled from space is also greatly improved in merged data as some areas can be sampled as frequently as 64% of the time (in days). The merged data presented here are validated through matchup analyses and by comparing them to the data sets obtained from individual missions. Further, a complete error budget for the final merged data products was developed which accounts for uncertainty associated with input water-leaving radiances and provides uncertainty levels for the output products (i.e. the chlorophyll concentration, the combined dissolved and detrital absorption coefficient and the particulate backscattering coefficient). These merged products and their uncertainties at each pixel were developed within the NASA REASON/MEaSUREs and ESA GlobColour projects and are available to the scientific community. Our approach has many benefits for the creation of unified Climate Data Records from satellite ocean color observations. © 2010 Elsevier Inc.


Puspitarini L.,University Paris Diderot | Lallement R.,University Paris Diderot | Vergely J.-L.,ACRI ST | Snowden S.L.,NASA
Astronomy and Astrophysics | Year: 2014

Three-dimensional (3D) interstellar medium (ISM) maps can be used to locate not only interstellar (IS) clouds, but also IS bubbles between the clouds that are blown by stellar winds and supernovae, and that are filled by hot gas. To demonstrate this and to derive a clearer picture of the local ISM, we compare our recent 3D maps of the IS dust distribution to the ROSAT diffuse X-ray background maps after removing heliospheric emission. In the Galactic plane, there is a good correspondence between the locations and extents of the mapped nearby cavities and the soft (0.25 keV) background emission distribution, showing that most of these nearby cavities contribute to this soft X-ray emission. Assuming a constant dust-to-gas ratio and homogeneous 106 K hot gas filling the cavities, we modeled the 0.25 keV surface brightness in a simple way along the Galactic plane as seen from the Sun, taking the absorption by the mapped clouds into account. The data-model comparison favors the existence of hot gas in the solar neighborhood, the so-called Local Bubble (LB). The inferred average mean pressure in the local cavities is found to be on the order of 10 000 cm-3 K, in agreement with previous studies, providing a validation test for the method. On the other hand, the model overestimates the emission from the huge cavities located in the third quadrant. Using CaII absorption data, we show that the dust-to-CaII ratio is very low in this region, implying there is a large quantity of lower temperature (non-X-ray emitting) ionized gas and, as a consequence, a reduction in the volume filled by hot gas, explaining at least part of the discrepancy. In the meridian plane, the main two brightness enhancements coincide well with the LB's most elongated parts and chimneys connecting the LB to the halo, but no particular nearby cavity is found towards the enhancement in the direction of the bright North Polar Spur (NPS) at high latitude. We searched in the 3D maps for the source regions of the higher energy (0.75 keV) enhancements in the fourth and first quadrants. Tunnels and cavities are found to coincide with the main bright areas; however, no tunnel or cavity is found to match the low-latitude b ≳ 8°, brightest part of the NPS. In addition, the comparison between the 3D maps and published spectral data do not favor the nearby cavities being located within ~200 pc as potential source regions for the NPS. Those examples illustrate the potential use of more detailed 3D distributions of the nearby ISM for interpreting the diffuse soft X-ray background. © ESO, 2014.


Sicard P.,ACRI ST | Dalstein-Richier L.,ACRI ST | Vas N.,Giefs Groupe International Detudes Sur Les Forets Sud Europeennes
Environmental Pollution | Year: 2011

In the South-Eastern French Mediterranean region, high ozone concentrations were measured since many years and specific symptoms like chlorotic mottles were detected on Arolla pines. We presented results for the 2000-2008 period concerning the trend analysis for ambient ozone concentrations and related forest damages, with the Mann and seasonal Kendall tests. Ozone precursor's emissions from Europe have been reduced over the last 20 years. Decreases in annual averages, median, 25th and 98th percentiles and maxima values were found. The seasonal trend analysis for the high-lying stations showed a decreasing trend for the warm season, when main ozone production is the photochemistry, and an increase for the cold period, caused by a reduced ozone titration. Statistics on Arolla Pine reveal strong correlations between mottling intensity and the high ozone concentrations. Finally, decreases for the ozone concentrations, and associated statistics, AOT40 values and for the mottling intensity on conifers needles were observed. © 2010 Elsevier Ltd. All rights reserved.


Saulquin B.,ACRI ST | Hamdi A.,Institute des Milieux Aquatiques | Gohin F.,French Research Institute for Exploitation of the Sea | Populus J.,French Research Institute for Exploitation of the Sea | And 2 more authors.
Remote Sensing of Environment | Year: 2013

The availability of light in the water column and at the seabed determines the euphotic zone and constrains the type and the vertical distribution of algae species. Light attenuation is traditionally quantified as the diffuse attenuation coefficient of the downwelling spectral irradiance at wavelength 490nm (Kd490) or the photosynthetically available radiation (KdPAR). Satellite observations provide global coverage of these parameters at high spatial and temporal resolution and several empirical and semi-analytical models are commonly used to derive Kd490 and KdPAR maps from ocean colour satellite sensors. Most of these existing empirical or semi-analytical models have been calibrated in open ocean waters and perform well in these regions, but tend to underestimate the attenuation of light in coastal waters, where the backscattering caused by the suspended matters and the absorption by the dissolved organic matters increase light attenuation in the water column.We investigate two relationships between KdPAR and Kd490 for clear and turbid waters using MERIS reflectances and the spectral diffuse attenuation coefficient Kd(λ) developed by Lee (2005). Satellite-derived fields of Kd490 and modelled KdPAR are evaluated using coincident in-situ data collected over the world in both clear and turbid waters, and by using Ecolight simulations. Temporal means at 250m resolution of KdPAR and euphotic depth were computed over the period 2005-2009 for European coastal waters. These mean data were cross-tabulated with in-situ data of kelp (Laminaria hyperborea) and seagrass (Posidonia oceanica), respectively observed at locations on Atlantic and Mediterranean shores where the light is taken as the limiting factor to the depth distribution for these species. The minima observed for P. oceanica, in percent of energy, are very close to 1% of surface irradiance, the historical threshold known as euphotic depth as defined by Ryther (1956). Real estimates of the surface irradiance (Frouin, 1989) are used in conjunction with the estimated KdPAR to calculate the residual energy at the lower limit of P. oceanica and L. hyperborea in mol·photons·m-2·day-1 as a complement to the usual fraction of the surface energy. We show that the observed values, in terms of energy, for both species were equivalent to the values reported in the literature. © 2012 Elsevier Inc.


Bruniquel J.,ACRI ST
European Space Agency, (Special Publication) ESA SP | Year: 2016

The Sentinel-3 Mission Performance Centre (S-3 MPC) is one of the facility part of the Payload Data Ground Segment (PDGS). It and aims at controlling the quality of all generated products, from L0 to L2. The S-3 MPC is composed of a Coordinating Centre (CC), where the core infrastructure is hosted, which is in charge of the main routine activities (especially the quality control of data) and the overall service management. Expert Support Laboratories (ESLs) are involved in calibration and validation activities and provide specific assessment of the products (e.g., analysis of trends, ad hoc analysis of anomalies, etc.). The S-3 MPC interacts with the Processing Archiving Centers (PACs) and the Marine Centre at EUMETSAT.


Welsh B.Y.,University of California at Berkeley | Lallement R.,University of Versailles | Vergely J.-L.,ACRI ST | Raimond S.,University of Versailles
Astronomy and Astrophysics | Year: 2010

Aims: We present new high resolution (R > 50 000) absorption measurements of the NaI doublet (5889-5895 Å) along 482 nearby sight-lines, in addition to 807 new measurements of the CaII K (3933 Å) absorption line. We have combined these new data with previously reported measurements to produce a catalog of absorptions towards a total of 1857 early-type stars located within 800 pc of the Sun. Using these data we have determined the approximate 3-dimensional spatial distribution of neutral and partly ionized interstellar gas density within a distance-cube of 300 pc from the Sun. Methods: All newly recorded spectra were analyzed by means of a multi-component line profile-fitting program, in most cases using simultaneous fits to the line doublets. Normalized absorption profiles were fitted by varying the velocity, doppler width and column density for all intervening interstellar clouds. The resulting total column densities were then used in conjunction with the Hipparcos distances of the target stars to construct inversion maps of the 3D spatial density distribution of the NaI and CaII bearing gas. Results: A plot of the equivalent width of NaI versus distance reveals a wall of neutral gas at ∼80 pc that can be associated with the boundary wall to the central rarefied Local Cavity region. In contrast, a similar plot for the equivalent width of CaII shows no sharply increasing absorption at 80 pc, but instead we observe a slowly increasing value of CaII equivalent width with increasing sight-line distance sampled. Low values for the volume density of NaI (n NaI < 10 -9 cm -3) are generally found within 50 pc of the Sun, whereas values in the range 10 -8 > n NaI > 10 -10 cm -3 are found for sight-lines with distance >300 pc. Both high and low values of the volume density of CaII (n CaII) are found for sight-lines <30 pc, dependent on whether local gas cloudlets are encountered. For distances >100 pc a value of n CaII ∼ 10 -9 cm -3 is typical for most sight-lines, indicating that the distribution of CaII bearing gas is fairly uniform throughout the general ISM. Our three maps of the 3D spatial distribution of local neutral NaI absorption extend and improve upon the accuracy of similar maps initially presented by Lallement et al. (2003, A&A, 411, 447), with many new neutral interstellar gas features (such as low neutral density gas tunnels) in the local interstellar medium now being revealed for the first time. The maps of the 3D distribution of partially ionized CaII gas are the first of their kind to be presented and exhibit many spatial similarities to those of their equivalent NaI absorption maps. A major finding from both sets of maps is that the low density Local Cavity region is surrounded by a highly fragmented wall of higher density NaI and CaII gas clouds. The appearance of this broken boundary may be linked to the purported explosive origin of the Local Cavity. Maps of the distribution of CaII gas density reveal the presence of many partially ionized low density cloudlets that reside within the Local Cavity, and their newly derived 3D spatial contours confirm previous observations of the local gas by Redfield & Linsky (2008, ApJ, 673, 283). Both the NaI and CaII maps suggest that the Local Cavity may contain several low density sub-cavities that are surrounded by thin filaments of neutral and/or partially ionized gas. However, further observations will be required to confirm the existence of a collection of cell-like interstellar cavities. The new maps also reveal several sight-lines where CaII absorption is high and the corresponding NaI absorption is low, and vice-versa. Such regions are probably influenced by the effects of the local stellar ionization field which can significantly affect the observed NaI/CaII column density ratio. Plots of this ratio as a function of distance for stars located near to the galactic plane show values in the range 0.1 to 1.0 for sight-lines with distances <80 pc. However, ratio values of between 0.5 and 20 are typical for more distant sight-lines. The highest values of the NaI/CaII ratio are found towards l ∼ 150° in the direction of the Taurus dark clouds, with ratio values in the narrower range of 0.1 to 5 being found in galactic quadrant 3. © 2010 ESO.

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