FIRST RESULTS FROM VIRGO,THE EXPERIMENT FOR HELIOSEISMOLOGY AND SOLAR IRRADIANCE MONITORING ON SOHO

First results from the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and Heliospheric Observatory) are reported. The observations started mid-January 1996 for the radiometers and sunphotometers and near the end of March for the luminosity oscillation imager. The performance of all the instruments is very good, and the time series of the first 4–6 months are evaluated in terms of solar irradiance variability, solar background noise characteristics and p-mode oscillations. The solar irradiance is modulated by the passage of active regions across the disk, but not all of the modulation is straightforwardly explained in terms of sunspot flux blocking and facular enhancement. Helioseismic inversions of the observed p-mode frequencies are more-or-less in agreement with the latest standard solar models. The comparison of VIRGO results with earlier ones shows evidence that magnetic activity plays a significant role in the dynamics of the oscillations beyond its modulation of the resonant frequencies. Moreover, by comparing the amplitudes of different components ofp -mode multiplets, each of which are influenced differently by spatial inhomogeneity, we have found that activity enhances excitation.     

Results from the Eso Large Program on Transneptunian Objects and Centaurs

BVRI photometry of 107 TNOs and Centaurs establishes the range of spectral gradients to be between –5 to 55%/100 nm (with one exception). A cluster of very red Cubewanos is firmly identified in orbits of low inclination and eccentricity beyond 40 AU from the Sun. Further correlations between surface colours and dynamical parameters (inclination and perihelion distance) are suggested for Cubewanos and scattered disk objects, but lack complete confidence for their reality. Plutinos and Centaurs do not show any clear correlation between surface colours and orbital parameters. We present in this paper 12 spectra obtained in the visible region and nine of them for which we obtained also near infrared spectra up to 2.4 microns. A few other objects have been observed, but the data are still under reduction and analysis. The principal reported results obtained are: (i) a wide range of visible slopes; (ii) evidence for surface variations on 2001 PT₁₃; and (iii) possible detection of few percent of water ice (1999 TC_36}, 2000 EB₁₇₃, 1999 DE₉, 2001 PT₁₃, 2000 QC₂₄₃, 1998 SG₃₅).     

Spatial distribution of soil shear-wave velocity and the fundamental period of vibration – a case study of the Saguenay region,Canada

The spatial distribution of soil shear-wave velocity and the fundamental period of vibration were selected as input parameters for the determination of potential seismic site effects in the Saguenay region, Canada. The methodology used in this study involved three clear steps. First, a 3D geological model of the surficial deposits was built taking into consideration the type, spatial distribution and thickness of the deposits. Second, representative average V_s values were determined for each of the major soil units. Finally, the average shear-wave velocity from the ground surface to bedrock (V_sav), the shear-wave velocity of the upper 30 m (V_s30) and the fundamental site resonance period (T₀) were calculated over a regular grid for the study area. The results include the spatial distribution of the fundamental site resonance period, the average shear-wave velocity in the first 30 m of the ground and the spatial distribution of National Building Code of Canada seismic soil classes for the Saguenay region.     

Courbes Intensité–Durée–Fréquence (IDF): comparaison des estimateurs des durées partielles et des maximums annuels

Résumé

Cette étude compare, pour la région sud du Québec (Canada), différents estimateurs des courbes intensité–durée–fréquence (IDF) basés sur les séries de durées partielles (SDP) et sur celles des maximums annuels (SMA). Deux modèles ont été considérés pour les SMA, le premier utilisant un paramètre local (SMA-1), et le second utilisant deux paramètres locaux (SMA-2). Pour les SDP, les séries ont été construites en fixant, d'une part, un seuil régional (SDP-1) et, d'autre part, le nombre moyen régional de dépassements du seuil (SDP-2). Les quantiles et les intervalles de confiance à 90% des différents modèles ont été estimés et comparés. Le modèle SDP-1 a été finalement retenu puisque, d'après la littérature, il conviendrait à une région comme celle sous étude dont l'hétérogénéité est raisonnable. Par ailleurs, le modèle SDP-1 reproduit relativement bien les quantiles et probabilités empiriques. Les quantiles générés, à chaque site, par ce modèle régional sont comparés à ceux obtenus à partir d'un modèle SDP local.

Citation Kingumbi, A. & Mailhot, A. (2010) Courbes Intensité–Durée–Fréquence (IDF): comparaison des estimateurs des durées partielles et des maximums annuels. Hydrol. Sci. J. 55(2), 162–176.     

Yields of suspended sediment and dissolved solids from the Andean basins of Ecuador

Abstract

Water discharge and suspended and dissolved sediment data from three rivers (Napo, Pastaza and Santiago) in the Ecuadorian Amazon basin and a river in the Pacific basin (Esmeraldas) over a 9-year period, are presented. This data set allows us to present: (a) the chemical weathering rates; (b) the erosion rates, calculated from the suspended sediment from the Andean basin; (c) the spatio-temporal variability of the two regions; and (d) the relationship between this variability and the precipitation, topography, lithology and seismic activity of the area. The dissolved solids load from the Esmeraldas basin was 2 × 10⁶ t year^-1, whereas for the Napo, Pastaza and Santiago basins, it was 4, 2 and 3 × 10⁶ t year^-1, respectively. For stations in the Andean piedmont of Ecuador, the relationship between surface sediment and the total sediment concentration was found to be close to one. This is due to minimal stratification of the suspended sediment in the vertical profile, which is attributed to turbulence and high vertical water speeds. However, during the dry season, when the water speed decreases, sediment stratification appears, but this effect can be neglected in the sediment flux calculations due to low concentration rates. The suspended sediment load in the Pacific basin was 6 × 10⁶ t year^-1, and the total for the three Amazon basins was 47 × 10⁶ t year^-1. The difference between these contributions of the suspended sediment load is likely due to the tectonic uplift and the seismic and volcanic dynamics that occur on the Amazon side.

Editor Z.W. Kundzewicz

Citation Armijos, E., Laraque, A., Barba, S., Bourrel, L., Ceron, C., Lagane, C., Magat, P., Moquet, J.-S., Pombosa, R., Sondag, F., Vauchel, P., Vera, A., and Guyot, J.L., 2013. Yields of suspended sediment and dissolved solids from the Andean basins of Ecuador. Hydrological Sciences Journal, 58 (7), 1478–1494.     

Evaluation of hydrocarbon pollution in marine sediments of Sfax coastal areas from the Gabes Gulf of Tunisia,Mediterranean Sea

The Tunisian environmental legislation that follows the EC Directives requires monitoring of persistent, toxic and bio-accumulated substances commonly considered as hazardous substances. In order to comply with this requirement, samples of sea water, sediment and biota from the urbanized and industrialized coast line of Sfax city are investigated. This study presents the results of petroleum hydrocarbon content, distribution and probable origin (anthropogenic and/or biogenic) in 16 intertidal sediments of Sfax coastal area. Alkane distribution indices and hydrocarbon distribution patterns are used to identify natural and anthropogenic input. Non-aromatic hydrocarbons present a high concentration with a range varying from 180 to 1,400 μg/g of dry sediment. The total concentrations of polycyclic aromatic hydrocarbons (PAHs) varied from 0.41 to 5.6 μg/g dry weight. These concentrations are comparable to other marine areas that receive important inputs. n-Alkanes with carbon number ranging from 15 to 35 are identified to be derived from both biogenic and anthropogenic sources in varying proportions. Pristane/phytane ratio shows values lower than 1.4 suggesting the presence of petroleum contamination. This is confirmed by the presence of a large group of unresolved complex mixture and the identification of hopanes with predominant C29 and C30 compounds and steranes with predominance of C27 over C28 and C29 compounds. Ratios of selected PAH concentrations indicate petrogenic and pyrolytic origin of hydrocarbons. Anthropogenic hydrocarbon inputs were more apparent at sites associated with industrial discharges, shipping activities and sewage outfalls.     

Estimating Sensible and Latent Heat Fluxes over an Inland Water Body Using Optical and Microwave Scintillometers

Boundary-Layer Meteorology - Observations of turbulent heat fluxes over inland water bodies are scarce despite being critical to adequate lake parametrization for numerical weather forecast and...     

A model of dimethylsulfide dynamics for the subtropical North Atlantic

Dimethylsulfide (DMS) is a volatile sulfur compound produced by the marine biota. The flux of DMS to the atmosphere may act on climate via aerosol formation. It is therefore important to improve our understanding of the processes that regulate sea surface DMS concentrations for eventual inclusion into climate models. In order to simulate the dynamics of DMS concentrations in the mixed layer, a model of DMS production was developed and calibrated against a 1 year time-series of DMS and DMSP (dissolved and particulate) data collected in the Sargasso Sea at Hydrostation ‘S’. The model reproduces the observed divergence between the seasonal cycles of particulate DMSP, the DMS precursor produced by algae, and DMS produced through the microbial loop from the cleavage of dissolved DMSP. DMSP_p (particulate) reaches its maximum in the spring whereas DMSP_d (dissolved) and DMS reach maximum concentrations in summer. Several parameters had to vary seasonally and with depth in order to reproduce the data, pointing out the importance of physiological and structural changes in the plankton food web. These parameters include the intracellular S(DMSp):N ratio, the C:Chl ratio and the sinking rates of phytoplankton and detritus. For the Sargasso Sea, variations in the solar zenithal angle, which co-vary with the seasonal variations in the depth of the mixed layer, proved to be a convenient signal to drive the seasonal variation in the structure and dynamics of the plankton. Variations of the temperature and photosynthetically active radiation also help to reproduce the short-term variability of the annual S cycle. Results from a sensitivity analysis show that variations in DMSP_p are dependent mostly on parameters controlling phytoplankton biomass, whereas DMS is dependent mostly on variables controlling phytoplankton productivity.