Wave effects in global ocean modeling: parametrizations vs. forcing from a wave model

One of the main challenges of the Copernicus Marine Service is the implementation of coupled ocean/waves systems that accurately estimate the momentum and energy fluxes provided by the atmosphere to the ocean. This study aims to investigate the impact of forcing the Nucleus for European Modelling of the Ocean (NEMO) ocean model with forecasts from the wave model of Météo-France (MFWAM) to improve classical air-sea flux parametrizations, these latter being mostly driven by the 10-m wind. Three wave-related processes, namely, wave-state-dependent stress, Stokes drift-related effects (Stokes-Coriolis force, Stokes drift advection on tracers and on mass), and wave-state-dependent surface turbulence, are examined at a global scale with a horizontal resolution of 0.25°. Three years of sensitivity simulations (2014–2016) show positive feedback on sea surface temperature (SST) and currents when the wave model is used. A significant reduction in SST bias is observed in the tropical Atlantic Ocean. This is mainly due to the more realistic momentum flux provided by the wave model. In mid-latitudes, the most interesting impact occurs during the summer stratification, when the wind is low and the wave model produces a reduction in the turbulence linked with wave breaking. Magnitudes of the large-scale currents in the equatorial region are also improved by 10% compared to observations. In general, it is shown that using the wave model reduces on average the momentum and energy fluxes to the ocean in tropical regions, but increases them in mid-latitudes. These differences are in the order of 10 to 20% compared with the classical parametrizations found in stand-alone ocean models.     

FVCOM model estimate of the location of Air France 447

On June 1, 2009, Air France AF447 disappeared in the Equatorial Atlantic Ocean en route from Rio de Janeiro, Brazil, to Paris, France. On June 6–19, 2009, bodies and debris from the aircraft were recovered floating in the equatorial ocean. This paper describes efforts on using the global–local nested finite volume community ocean model (FVCOM) to model reversely the tracks of bodies and debris back to the time of the crash and to help searchers locate the cockpit voice and flight data recorders and learn why this tragic accident occurred. To validate the reliability and reality of FVCOM, eight surface drifters were deployed by the French Bureau d’Enquêtes et d’Analyses pour la sécurité de l’aviation civile (BEA) near the last known position in early June 2010 for a period of 3?weeks. These drifter data were used to optimize the spatial and temporal correlation scales of the adaptive sampling data assimilation method of FVCOM. Applying an optimized FVCOM system to assimilate all available drifter- and float-tracking-derived currents in May–June 2009 under three different wind conditions, we reproduced the June 2009 current fields in the area near the LKP and used these fields to reversely track bodies and debris from locations where they were found to the time when the crash occurred. Possible locations for the crashed plane were suggested based on our model results and were made available to the French investigators and the Woods Hole Oceanographic Institution REMUS autonomous underwater vehicle Operations Group who successfully located the aircraft debris field in April 2011 on the seafloor at a depth of 3,900?m.     

Multi-hydro hydrological modelling of a complex peri-urban catchment with storage basins comparing C-band and X-band radar rainfall data

ABSTRACT

The spread of impervious surfaces in urban areas combined with the rise in the intensity of rainfall events as a result of climate change has led to dangerous increases in storm water flows. This paper discusses a new implementation of the fully distributed hydrological model Multi-Hydro (developed at École des Ponts ParisTech), when operating storage basins, and its ability to deal with high-resolution radar rainfall data. The peri-urban area of Massy (south of Paris, France) was selected as a case study for having six of these drainage facilities, used extensively in flood control. Two radar rainfall datasets with different spatiotemporal resolutions were used: Météo-France’s PANTHER rainfall product (C-band) and ENPC’s X-band DPSRI. The rainfall spatiotemporal variability was analysed statistically using Universal Multifractals (UM). Finally, to validate the application, the water level simulations were compared with local measurements in the Cora storage basin located next to the catchment’s single outlet.     

Advanced insights into sources of vertical velocity in the ocean

Estimating vertical velocity in the oceanic upper layers is a key issue for understanding ocean dynamics and the transport of biogeochemical elements. This paper aims to identify the physical sources of vertical velocity associated with sub-mesoscale dynamics (fronts, eddies) and mixed-layer depth (MLD) structures, using (a) an ocean adaptation of the generalized Q-vector form of the ω-equation deduced from a primitive equation system which takes into account the turbulent buoyancy and momentum fluxes and (b) an application of this diagnostic method for an ocean simulation of the Programme Océan Multidisciplinaire Méso Echelle (POMME) field experiment in the North-Eastern Atlantic. The approach indicates that w-sources can play a significant role in the ocean dynamics and strongly depend on the dynamical structure (anticyclonic eddy, front, MLD, etc.). Our results stress the important contribution of the ageostrophic forcing, even under quasi-geostrophic conditions. The turbulent w-forcing was split into two components associated with the spatial variability of (a) the buoyancy and momentum (Ekman pumping) surface fluxes and (b) the MLD. Process (b) represents the trapping of the buoyancy and momentum surface energy into the MLD structure and is identified as an atmosphere/oceanic mixed-layer coupling. The momentum-trapping process is 10 to 100 times stronger than the Ekman pumping and is at least 1,000 times stronger than the buoyancy w-sources. When this decomposition is applied to a filamentary mixed-layer structure simulated during the POMME experiment, we find that the associated vertical velocity is created by trapping the surface wind-stress energy into this structure and not by Ekman pumping.     

Model ALADIN as regional climate model for Central and Eastern Europe

Results obtained with two versions of the Limited Area Model (LAM) ALADIN over differently sized integration domains (large, intermediate and small) in the European area are presented in order to investigate both the general model performance and the influence of domain choice on the quality of obtained results. The aim is also to illustrate the issues related to the strategy of selection of the optimal integration domain. Each of these studies has been performed with two versions of the ALADIN model: the first one is ALADIN-CLIMATE developed at CNRM/Météo-France, the second one is ALADIN-CLIMATE/CZ prepared at the Czech Hydrometeorological Institute (CHMI). This leaves us with total of six experiments forced by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-40 reanalysis data. The west Balkan domain covering Bulgaria is used as an evaluation region for investigation of the temporal and spatial properties of simulated precipitation and temperature fields. This region has been selected for its challenging orography making the results obtained here a valuable source for studies leading to further developments in climate modeling. It was found that size of the domain strongly affects the quality of obtained results. We have found that the largest domain reproduces the spatial characteristics of climate (such as bias) very well, but its use results in a poor representation of temporal aspects, which are however captured very well in experiments over both smaller domains. Our findings suggest that there is no optimal choice of domain size, securing the best results for both spatial and temporal evaluation.     

Ein Differenzengleichungssystem zur Ermittlung instationärer Bewegungen in einem Meer mit geringer Turbulenzreibung

Zusammenfassung Es wird ein auf Probleme der dynamischen Meteoro-Hydrographie erfolgreich angewandtes Differenzengleichungssystem er?rtert, dessen numerische Stabilit?t, unabh?ngig von der geographischen Breite, auch bei gro?er Tiefe und sehr kleinem Horizontaldiffusionskoeffizienten gew?hrleistet ist. Für Anwendungen auf meridional stark ausgedehnte Ozeane, z. B. bei Gezeitenrechnungen, werden die durch Verwendung von Kugelkoordinaten erforderlichen Erweiterungen abgeleitet.

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A system of finite difference equations for computations of instationary motions in an ocean with small eddy viscosity

Summary A system of finite difference equations successfully applied to some problems of dynamical meteoro-hydrography is discussed. Its numerical stability may also be fitted in cases of very small horizontal eddy diffusity and large depths independend of the latitude. For the purpose of applications to meridionally far extended oceans, for instance when dealing with tidal computations, the necessary completations due to the employment of spherical polar coordinates are derived.

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Un système d'équations aux différences finies permettant le calcul de mouvements non stationnaires dans une mer à faible frottement de turbulence

Résumé On discute d'un système d'équations aux différences finies appliqué avec succès à des problèmes de météoro-hydrographie dynamique. Du fait de sa stabilité numérique, indépendante de la latitude, ce système reste également valable dans le cas des grandes profondeurs et pour de très faibles coefficients de diffusion horizontale. Pour ses applications dans les océans à grande extension méridienne, par exemple aux calculs de marées, on en tire les développements que nécessite l'emploi de coordonnées sphériques.

     

A numerical study of the circulation and monthly-to-seasonal variability in the Caribbean Sea: the role of Caribbean eddies

This study examines the circulation and associated monthly-to-seasonal variability in the Caribbean Sea using a regional ocean circulation model. The model domain covers the region between 99.0 and 54.0°W and between 8.0 and 30.3°N, with a horizontal resolution of 1/6°. The ocean circulation model is driven by 6-hourly atmospheric reanalysis data from the National Center for Environmental Prediction and boundary forcing extracted from 5-day global ocean reanalysis data produced by Smith et al. (Mercator Newsletter 36:39–49, 2010), and integrated for 7 years. A comparison of model results with observations demonstrates that the regional ocean circulation model has skill in simulating circulation and associated variability in the study region. Analysis of the model results, as well as a companion model run that uses steady annual mean forcing, illustrates the role of Caribbean eddies for driving monthly-to-seasonal circulation variability in the model. It is found that vertically integrated transport between Nicaragua and Jamaica is influenced by the interaction between the density perturbations associated with Caribbean eddies and the Nicaraguan Ridge. The impact of Caribbean eddies squeezing through the Yucatan Channel is also discussed.     

Über das dickenwachstum des eises

Summary In this paper which refers to a short communication on the growth in thickness of ice published by F. Model in this journal, vol. 1 (1948) p. 104, attention is drawn to the fact that since 1867 an incorrectly determined coefficient of the heat conductivity of ice has been repeatedly employed in various computations. After giving the correct value, the author reports on his own experiences in the application of formulae concerning the growth in thickness of ice and suggests the introduction of a factor of reduction.

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Résumé En se référant à un bulletin par F. Mode1 paru dans ce journal, vol. 1 (1948) p. 104, l'auteur a tiré l'attention sur le fait que le coefficient de conductivité thermique de la glace qui a été employé à plusieurs reprises dans divers calculs depuis 1867 a été déterminé incorrectement. Après avoir donné le coefficient correct l'auteur rapporte ses propres expériences faites en applicant des formules relatives à la croissance en épaisseur de la glace et propose l'introduction d'un facteur de réduction.

     

Functioning of the avalanche starting zones which undergo snow-transport by wind: Field observations and computer modeling

For two years, three French and Swiss laboratories have been making field observations and measurements on two high altitude slopes in a Northern French Alps site. The aim of this work is to study the functioning of the avalanche sites which, in their starting zones, undergo snow-transport by wind. The experimental site is located in the French Alps, at 2,800 m, above Grenoble. It is an open area, equipped with an automatic meteorological station and an altitude laboratory. The two slopes that are studied face East. One of them is artificially released but the other has a natural avalanche activity. The investigations concern:

-snow deposition in avalanche starting zones;

-temporal evolution of the snowpack characteristics;

-avalanche release.

For the field observations and measurements, continuous recording of the meteorological conditions on the site, photogrammetrical techniques and two snow depth profiles, as well as stratigraphical snow profiles and video are used. The computer modeling is based on existing computer models developed by the CEMAGREF-Nivologie (ELSA) and the CEN/Météo-France (SAFRAN-CROCUS-MEPRA), which analyse the snowpack and its stability. The field observations and measurements aim at improving snow-transport by wind modeling modules, in order to improve their whole analysis.     

Erodibility of low‐compaction steep‐sloped reclaimed surface mine lands in the southern Appalachian region,USA

The use of loose spoils on steep slopes for surface coal mining reclamation sites has been promoted by the US Department of Interior, Office of Surface Mining for the establishment of native forest, as prescribed by the Forest Reclamation Approach (FRA). Although low‐compaction spoils improve tree survival and growth, erodibility on steep slopes was suspected to increase. This study quantified a combined K_C factor (combining the effects of the soil erodibility K factor and cover management C) for low compaction, steep‐sloped (>20°) reclaimed mine lands in the Appalachian region, USA. The combined K_C factor was used because standard Unit Plot conditions required to separate these factors, per Revised Universal Soil Loss Equation (RUSLE) experimental protocols, were not followed explicitly. Three active coal mining sites in the Appalachian region of East Tennessee, each containing four replicate field plots, were monitored for rainfall and sediment yields during a 14‐month period beginning June 2009. Average cumulative erosivity for the study sites during the monitoring period was measured as 5248.9 MJ·mm·ha^?1·h^?1. The K_C ranged between 0.001 and 0.05 t·ha·h·ha^?1·MJ^?1·mm^?1, with the highest values occurring immediately following reclamation site construction as rills developed (June – August 2009). The K_C for two study sites with about an 18–20 mm spoil D₈₄ were above 0.01 t·ha·h·ha^?1·MJ^?1·mm^?1 during rill development, and below 0.003 t·ha·h·ha^?1·MJ^?1·mm^?1 after August 2009 for the post‐rill development period. The K_C values for one site with a 40 mm spoil D₈₄ were never above 0.008 t·ha·h·ha^?1·MJ^?1·mm^?1 and also on average were lower, being more similar to the other two sites after the rill development period. Based on an initial K_C factor (K_e) measured during the first few storm events, the average C factor (C_e) was estimated as 0.58 for the rill development period and 0.13 for the post‐rill development period. It appears that larger size fractions of spoils influence K_C and C_e factors on low‐compaction steep slopes reclamation sites. Copyright © 2013 John Wiley & Sons, Ltd.     

Radiolarian‐based study on the fabric and the formation process of the Early Cretaceous mélange near Zhongba,Yarlung–Tsangpo Suture Zone,southern Tibet

The Yarlung–Tsangpo Suture Zone (YTSZ), as the southernmost and youngest among the sutures that subdivides the Tibetan Plateau into several east–west trending blocks, marks where the Neo‐Tethys was consumed as the Indian continent moved northward and collided against the Eurasian continent. Mélanges in the YTSZ represent the remnants of the oceanic plate through subduction and collision. Mélanges are characterized by a highly sheared volcanoclastic or siliceous mudstone matrix including blocks of chert, claystone, and basalt. Detailed radiolarian analyses are conducted on the mélange near Zhongba County. Macroscopic, mesoscopic, and microscopic observations are combined in order to elucidate the relationships among age, lithology, and structure of blocks in the mélange. Reconstructed ocean plate stratigraphy includes Lower Jurassic limestone within the chert sequence accumulated at a depth near the CCD (Unit 2), Upper Jurassic thin‐bedded chert interbedded with claystone deposited in the wide ocean basin (Unit 3), and Lower Cretaceous chert with siliceous mudstone (Units 4 and 5), representing the middle parts of ocean plate stratigraphy. The results highlight the fabric of brecciated chert on mesoscopic scale, which is thought to be due to localized overpressure. The formation of mesoscopic and microscopic block‐in‐matrix fabrics in the mélange is proposed for the chert and siliceous mudstone bearing different extents of consolidation and competence during the progressive deformation of accreted sediments at shallow‐level subduction.     

Deep water observations of extreme waves with moored and free GPS buoys

Point-positioning GPS-based wave measurements were conducted by deep ocean (over 5,000 m) surface buoys moored in the North West Pacific Ocean in 2009, 2012, and 2013. The observed surface elevation bears statistical characteristics of Gaussian, spectrally narrow ocean waves. The tail of the averaged spectrum follows the frequency to the power of ?4 slope, and the significant wave height and period satisfies the Toba’s 3/2 law. The observations compare well with a numerical wave hindcast. Two large freak waves exceeding 13 m in height were observed in October 2009 and three extreme waves around 20 m in height were observed in October 2012 and in January 2013. These extreme events are associated with passages of a typhoon and a mid-latitude cyclone. Horizontal movement of the buoy revealed that the orbital motion of the waves at the peak of the wave group mostly exceed the weakly nonlinear estimate. For some cases, the orbital velocity exceeded the group velocity, which might indicate a breaking event but is not conclusive yet.     

Bodenfaunistische Untersuchungen in Aare und Rhein

Summary In 1969–1972 the benthos of the rivers Aare (near Beznau) and Rhine (near Kaiseraugst) was investigated. At every two stations of both rivers, we collected 8 samples regularly distributed over the river width. Both collecting and counting were performed quantitatively. Physical and chemical data, and grain size analyses of the substratum are given for both rivers. The results of the extensive counts were summarized in a list of quantitative abundance. The benthic biocoenoses are dominated in both rivers by oligochaetes and chironomids; in the Aare the trichopteran larvae ofHydropsyche sp. are also highly abundant. In the Aare 79 species or genera and an average of 48,100 individuals per square meter were collected. This benthic fauna is richer and denser than in the Rhine, where 41 species or genera and an average of 11,400 individuals per square meter were recorded. The distribution of the organisms is inhomogeneous (contagious), and within a square meter the total number of individuals per 855 cm² ranged between 4.056 and 23,140. In the Aare the average biomass is 8.6–41.5 g/m², again higher than in the Rhine (0.5–3.1 g/m²). The Rhine river bed is covered with gravel and sand, whereas in the Aare the bed is muddy. As the physical and chemical conditions are quite the same in both rivers, we relate the different population densities to the differences in the substratum.

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Résumé En 1969–1972, les invertébrés de l'Aar (près de Beznau) et du Rhin (près de Kaiseraugst) ont été examinés. Deux stations de prélèvement ont été choisies pour chaque cours d'eau et à chacune d'elles, 8 échantillons ont été pris, répartis régulièrement sur toute la largeur. Les organismes ont été collectionnés et dénombrés d'une manière quantitative. Pour comparer la biologie des deux cours d'eau, on a étudié les résultats physico-chimiques et les analyses de granulométrie du fond. Les résultats des nombreux comptages ont été résumés dans une liste quantitative d'abondance. Dans les deux cours d'eau, les oligochètes et les chironomides dominent les biocénoses benthiques; en outre, dans l'Aar, la larve du trichoptèreHydropsyche sp. joue un r?le assez important. L'Aar, contenant 79 espèces ou genres et en moyenne 48 100 individus par m², est plus riche et plus dense en organismes benthiques répartition des organismes est très hétérogène (contagieuse) et sur 1 m², le nombre total des individus par 855 cm² varie entre 4056 et 23 140. Enfin, dans l'Aar, on trouve aussi une biomasse plus grande (en moyenne 8,6–41,5 g/m²) que dans le Rhin (en moyenne 0,5–3,1 g/m²). La nature du fond du Rhin est graveleuse-sablonneuse, tandis que dans l'Aar le limon prédomine. Puisque les conditions physico-chimiques sont assez semblables dans les deux cours d'eau, la différence de densité des populations est expliquée par la nature même des deux types de substratum.

     

Numerical seasonal predictions using global climate models. Researches on the long range forecasting at Météo France

Since 1995, Météo France has engaged important research works concerning seasonal forecasting within the framework of projects of the European Union. One of these projects is described here. The main goal of the project PROVOST was to evaluate the potential of predictability on seasonal and monthly time-scales of some Global Climate Models (GCM) running separately ensembles of integrations, or gathered in a multimodel ensemble of predictions. The result is that the deterministic skill and the probabilistic skill are both improved by increasing the ensemble size and by merging different models.     

Ionospheric Scintillation and Dynamics of Fresnel-Scale Irregularities in the Inner Region of the Equatorial Ionization Anomaly

This paper reports differences in the occurrence statistics of global positioning system (GPS) L-band scintillations at observational sites located in the inner regions of the northern and southern crests of the equatorial ionization anomaly. Ground-based GPS data acquired at the closed magnetically aligned stations of Manaus (3.1°S; 59.9°W; dip lat. 6.2°N) and Cuiabá (15.5°S; 56.1°W; dip. lat. 6.2°S), Brazil, from December 2001 to February 2007 are used in the analysis. The drift dynamics of Fresnel-scale ionospheric irregularities at the southern station of Cuiabá are also investigated. Only geomagnetically quiet days with the sum of daily Kp < 24 were used in the analysis statistics and in the irregularity drift studies. The results reveal a clear dependence of the scintillation occurrence with the solar activity, but there exists an asymmetry in the percentage of scintillation occurrence between the two stations throughout the period analyzed. The nocturnal occurrence of the scintillations over Cuiabá is predominantly larger than over Manaus, but this scenario seems to change with the decline in the solar activity (mainly during local post-midnight hours). A broad minimum and maximum in the scintillation occurrence appears to occur over both the stations, respectively, during the June solstice (winter) and December solstice (summer) months. The dynamics of the Fresnel-scale irregularities, as investigated from the estimations of the mean zonal drift velocities, reveals that the amplitude of the eastward drifts tends to reduce with the decline in the solar activity. The magnitude of the zonal drift velocities during the December solstice months is larger than during the equinoxes, with the differences being more pronounced at solar maximum years. Other relevant aspects of the observations, with complementary data from a low-latitude ionospheric model, are highlighted and discussed.     

Identification of runoff generation processes using combined hydrometric,tracer and geophysical methods in a headwater catchment in South Africa / Identification des processus de génération de l'écoulement par combinaison de méthodes hydrométriques,de traçage et géophysiques dans un bassin versant sud-africain

Résumé

Des mesures hydrométriques classiques et l'imagerie 2-D de résistivité électrique (IRE) détaillée ont été combinées avec le prélèvement de traceurs pour identifier les processus hydrologiques en jeu dans un bassin versant semi-aride de la province Cap-Oriental, en Afrique du Sud. L'étude des événements de précipitation et d'écoulement a souligné la forte relation qui existe entre les précipitations et les caractéristiques de la génération des écoulements. L'observation du potentiel hydrique du sol ainsi que du niveau d'eau souterraine a mis en évidence le développement d'une nappe perchée dans le sol. Ces résultats sont confirmés par des séparations d'hydrogrammes à base de traceurs et illustrent le rôle important des écoulements souterrains superficiels. L'étude par IRE a permis de mieux connaître la structure du sous-sol. Finalement, l'étude par IRE, combinée avec des mesures obtenues par réflectométrie en domaine temporel (TDR), a permis d'extrapoler à des mesures sélectives de teneur en eau. Pour récapituler, l'utilisation et la combinaison de différentes méthodes de terrain ont mené au développement d'un modèle conceptuel du fonctionnement hydrologique de ce bassin versant. Le rôle dominant des mécanismes de subsurface a été démontré.     

Impact of Indian ocean dipole on the coastal upwelling features off the southwest coast of India

A three-dimensional regional ocean model is used to examine the impact of positive Indian ocean dipole (pIOD) events on the coastal upwelling features at the southwest coast of India (SWCI). Two model experiments are carried out with different surface boundary conditions that prevailed in the normal and pIOD years from 1982 to 2010. Model experiments demonstrate the weakening of coastal upwelling at the SWCI in the pIOD years. The reduced southward meridional wind stress off the SWCI leads to comparatively lower offshore Ekman transport during August–October in the pIOD years to that in normal years. The suppressed coastal upwelling results in warmer sea surface temperature and deeper thermocline in the pIOD years during June–September. The offshore spatial extent of upwelled colder (<?22 °C) water was up to 75.5° E in August–September in normal years that was limited up to 76.2° E in pIOD years. The heat budget analysis reveals the decreased contribution of vertical entrainment process to the mixed layer cooling in pIOD years which is almost half of that of normal years in October. The net heat flux term shows warming tendency during May–November with a higher magnitude (+?0.4 °C day^?1) in normal years than pIOD years (+?0.28 °C day^?1). The biological productivity is found to reduce during the pIOD years as the concentration of phytoplankton and zooplankton decreases over the region of coastal upwelling at SWCI. Nitrate concentration in the pIOD years dropped by half during August–September and dropped by an order of magnitude in October as compared to its ambient concentration of 13 μmol L^?1 in normal years.     

Role of Ocean in the Variability of Indian Summer Monsoon Rainfall

Asian summer monsoon sets in over India after the Intertropical Convergence Zone moves across the equator to the northern hemisphere over the Indian Ocean. Sea surface temperature (SST) anomalies on either side of the equator in Indian and Pacific oceans are found related to the date of monsoon onset over Kerala (India). Droughts in the June to September monsoon rainfall of India are followed by warm SST anomalies over tropical Indian Ocean and cold SST anomalies over west Pacific Ocean. These anomalies persist till the following monsoon which gives normal or excess rainfall (tropospheric biennial oscillation). Thus, we do not get in India many successive drought years as in sub-Saharan Africa, thanks to the ocean. Monsoon rainfall of India has a decadal variability in the form of 30-year epochs of frequent (infrequent) drought monsoons occurring alternately. Decadal oscillations of monsoon rainfall and the well-known decadal oscillation in SST of the Atlantic Ocean (also of the Pacific Ocean) are found to run parallel with about the same period close to 60 years and the same phase. In the active–break cycle of the Asian summer monsoon, the ocean and the atmosphere are found to interact on the time scale of 30–60 days. Net heat flux at the ocean surface, monsoon low-level jetstream (LLJ) and the seasonally persisting shallow mixed layer of the ocean north of the LLJ axis play important roles in this interaction. In an El Niño year, the LLJ extends eastwards up to the date line creating an area of shallow ocean mixed layer there, which is hypothesised to lengthen the active–break (AB) cycle typically from 1 month in a La Niña to 2 months in an El Niño year. Indian monsoon droughts are known to be associated with El Niños, and long break monsoon spells are found to be a major cause of monsoon droughts. In the global warming scenario, the observed rapid warming of the equatorial Indian ocean SST has caused the weakening of both the monsoon Hadley circulation and the monsoon LLJ which has been related to the observed rapid decreasing trend in the seasonal number of monsoon depressions.     

Determination of Earth’s Transient and Equilibrium Climate Sensitivities from Observations Over the Twentieth Century: Strong Dependence on Assumed Forcing

Relations among observed changes in global mean surface temperature, ocean heat content, ocean heating rate, and calculated radiative forcing, all as a function of time over the twentieth century, that are based on a two-compartment energy balance model, are used to determine key properties of Earth’s climate system. The increase in heat content of the world ocean, obtained as the average of several recent compilations, is found to be linearly related to the increase in global temperature over the period 1965–2009; the slope, augmented to account for additional heat sinks, which is an effective heat capacity of the climate system, is 21.8 ± 2.1 W year m^?2 K^?1 (one sigma), equivalent to the heat capacity of 170 m of seawater (for the entire planet) or 240 m for the world ocean. The rate of planetary heat uptake, determined from the time derivative of ocean heat content, is found to be proportional to the increase in global temperature relative to the beginning of the twentieth century with proportionality coefficient 1.05 ± 0.06 W m^?2 K^?1. Transient and equilibrium climate sensitivities were evaluated for six published data sets of forcing mainly by incremental greenhouse gases and aerosols over the twentieth century as calculated by radiation transfer models; these forcings ranged from 1.1 to 2.1 W m^?2, spanning much of the range encompassed by the 2007 assessment of the Intergovernmental Panel on Climate Change (IPCC). For five of the six forcing data sets, a rather robust linear proportionality obtains between the observed increase in global temperature and the forcing, allowing transient sensitivity to be determined as the slope. Equilibrium sensitivities determined by two methods that account for the rate of planetary heat uptake range from 0.31 ± 0.02 to 1.32 ± 0.31 K (W m^?2)^?1 (CO₂ doubling temperature 1.16 ± 0.09–4.9 ± 1.2 K), more than spanning the IPCC estimated “likely” uncertainty range, and strongly anticorrelated with the forcing used to determine the sensitivities. Transient sensitivities, relevant to climate change on the multidecadal time scale, are considerably lower, 0.23 ± 0.01 to 0.51 ± 0.04 K (W m^?2)^?1. The time constant characterizing the response of the upper ocean compartment of the climate system to perturbations is estimated as about 5 years, in broad agreement with other recent estimates, and much shorter than the time constant for thermal equilibration of the deep ocean, about 500 years.     

De quelques champignons parasites d’organismes planctoniques du Léman

Résumé La présence d’environ vingt-cinq espèces de champignons parasites d’algues a été constatée récemment dans le Petit-lac (Léman). La plupart ont été observées pour la première fois dans cette région, trois espèces nouvelles ont été décrites:Zygorhizidium asterionellae, Rhizophidium tetragenum etR. mougeotiae. Certains de ces champignons parasites peuvent être la cause de véritables épidémies parmi les populations algales du lac et les décimer plus ou moins complètement en très peu de temps. Quelques problèmes soulevés par ces parasitoses ont été abordés, de nombreux points restent à éclaircir.

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Summary In the southwestern part of Lake of Geneva (Petit-Lac), 25 species of parasitic fungi (Chytridiales, Lagenidiales and Olpidiales) have been fond on algae and on pine pollen. Most of these species have been observed for the first time in this area, and three of them proved to be as not yet described:Zygorhizidium asterionellae, Rhizophidium tetragenum andR. mougeotiae. Some of these parasitic species cause real epidemics in the related host algae and are capable to decimate them more or less completely within a short time. Some problems related to this parasitism have been resolved, however, numerous questions are left to future research.

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Zusammenfassung Im südwestlichen Teil des Genfersees (Petit-Lac) wurden 25 Arten von parasitischen Pilze (Chytridiales, Lagenidiales und Olpidiales) auf Algen undPinuspollen festgestellt, Die meisten dieser Arten wurden für das Gebiet zum erstenmal beobachtet, und drei Arten erwiesen sich als noch nicht beschrieben:Zygorhizidium asterionellae, Rhizophidium tetragenum undR. mougeotiae. Einige parasitische Arten verursachen eigentliche Epidemien in den Kolonien der betreffenden Algenarten und verm?gen sie innert kurzer Zeit mehr oder weniger vollst?ndig zu dezimieren. Einige damit zusammenh?ngende Probleme konnten n?her erl?utert werden, aber viele Punkte bleiben noch unklar.