The Atlantic Multidecadal Oscillation in twentieth century climate simulations: uneven progress from CMIP3 to CMIP5

Decadal variability in the climate system from the Atlantic Multidecadal Oscillation (AMO) is one of the major sources of variability at this temporal scale that climate models must properly incorporate because of its climate impact. The current analysis of historical simulations of the twentieth century climate from models participating in the CMIP3 and CMIP5 projects assesses how these models portray the observed spatiotemporal features of the sea surface temperature (SST) and precipitation anomalies associated with the AMO. A short sample of the models is analyzed in detail by using all ensembles available of the models CCSM3, GFDL-CM2.1, UKMO-HadCM3, and ECHAM5/MPI-OM from the CMIP3 project, and the models CCSM4, GFDL-CM3, UKMO-HadGEM2-ES, and MPI-ESM-LR from the CMIP5 project. The structure and evolution of the SST anomalies of the AMO have not progressed consistently from the CMIP3 to the CMIP5 models. While the characteristic period of the AMO (smoothed with a binomial filter applied fifty times) is underestimated by the three of the models, the e-folding time of the autocorrelations shows that all models underestimate the 44-year value from observations by almost 50 %. Variability of the AMO in the 10–20/70–80 year ranges is overestimated/underestimated in the models and the variability in the 10–20 year range increases in three of the models from the CMIP3 to the CMIP5 versions. Spatial variability and correlation of the AMO regressed precipitation and SST anomalies in summer and fall indicate that models are not up to the task of simulating the AMO impact on the hydroclimate over the neighboring continents. This is in spite of the fact that the spatial variability and correlations in the SST anomalies improve from CMIP3 to CMIP5 versions in two of the models. However, a multi-model mean from a sample of 14 models whose first ensemble was analyzed indicated there were no improvements in the structure of the SST anomalies of the AMO or associated regional precipitation anomalies in summer and fall from CMIP3 to CMIP5 projects.     

Isotopes in the Hueco Bolson aquifer, Texas (USA) and Chihuahua (Mexico): local and general implications for recharge sources in alluvial basins

Stable isotope data for the Hueco Bolson aquifer (Texas, USA and Chihuahua, Mexico) distinguish four water types. Two types relate to recharge from the Rio Grande: pre-dam (pre-1916) river water with oxygen-18 and deuterium (δ¹⁸O, δD, ‰) from (?11.9, ?90) to (?10.1, ?82), contrasts with present-day river water (?8.5, ?74) to (?5.3, ?56). Pre-dam water is found beneath the Rio Grande floodplain and Ciudad Juárez, and is mixed with post-dam river water beneath the floodplain. Two other types relate to recharge of local precipitation; evidence of temporal change of precipitation isotopes is present in both types. Recharge from the Franklin and Organ Mountains plots between (?10.9, ?76) and (?8.5, ?60) on the global meteoric water line (GMWL), and is found along the western side of the Hueco Bolson, north of the Rio Grande. Recharge from the Diablo Plateau plots on an evaporation trend originating on the GMWL near (?8.5, ?58). This water is found in the southeastern Hueco Bolson, north of the river; evaporation may be related to slow recharge through fine-grained sediment. Pre-dam water, recognizable by isotope composition, provides information on groundwater residence times in this and other dammed river basins.     

Terremoti dell'Appennino Vogherese-Tortonese e la geologia della regione

Riassunto L'A. studia macro- e microsismicamente i terremoti del 14 giugno, 29 giugno e 15 dicembre 1945, determinandone la posizione delf'epicentio, che pei i primi due viene a cadere nell'Appennino Vogherese fra la Val Staffora e la Val di Nizza, per il terzo invece a N della congiungente Tortona-Alessandria. La profondita ipocentrale del terremoto del 29 giugno 1945 oscilla fra un valore minimo di 9 Km ottenuto macrosismicamente ed un valore massimo, ricavato per via microsismica, di 25 km; quello del 15 dicembre 1945 ha una profondità, microsismicamente calcolata sui 25 km; per quello del 14 giugno 1945 i risultati sono molto incerti. La scossa all'epicentro ha sempre nei tre sismi il carattere di sprofondamento.Posta a confronto colla struttura geologica della regione tale attività sismica non sembra derivare da un determinato elemento strutturale rilevabile; essa è probabilmente dovuta a sprofondamenti avvenuti a media profondità e presenta un'intensificazione in corrispondenza a direttrici tettoniche trasversali al locale andamento del corrugamento. I danni maggiori poi si possono mettere in stretto rapporto colla presenza di esigue formazioni alluvionali sciolte su roccia in posto.

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Summary The author studies macro-microseismically the earthquakes which we have ascertained on the 14^th of June, the 29^th of June and the 15^th of December in the year 1945, giving us the position of the epicentrum, which in the first two falls in Vogherese Appennino between Staffora and Nizza valleys, for the third instead north of Tortona-Alessandria connecting. The ipocentrum depth of the earthquake on the 29^th of June goes from a lowest value of 9 km had macro-seismically to a maximum value had micro-seismically of about 25 km. The 15^th of December one has a depth microseismically computed about 25 km, for the other on the 14^th of June the outcomes are very dubious.The skate at the ipocentrum has in all these three seisms the sinking type.Having made a comparison with the geological structure of the country such a seismical activity does not seem to come from a determinate structural relieving element; it is of course owed sinkings that we had in a middle depth and has an intensity which are in conformity with transversal tectonical directresses. The biggest damages can be put in strait relation with the presence of very little alluvial formations.

     

Detection of Miocene saucer‐shaped sills (offshore Senegal) via integrated interpretation of seismic,magnetic and gravity data

The Atlantic margin offshore Senegal has been explored by seismic reflection and GRAV‐MAG surveys. High‐amplitude, laterally transgressive seismic reflectors are found to coincide with gravimetric and magnetic highs. Once seismic data are integrated with potential fields modelling, these reflectors can be safely interpreted as saucer‐shaped igneous sills, up to some hundreds of metres thick, some km wide. The occurrence of hydrothermal vent complexes and forced folds in the stratigraphic sequence above the sills constrain the intrusion age to the Miocene. Field observations and in‐situ magnetic susceptibility measurements of Oligocene–Miocene and Quaternary igneous rocks emplaced in coastal Senegal support this interpretation.     

Comparing mixing-length models of the diabatic wind profile over homogeneous terrain

Models of the diabatic wind profile over homogeneous terrain for the entire atmospheric boundary layer are developed using mixing-length theory and are compared to wind speed observations up to 300 m at the National Test Station for Wind Turbines at Høvsøre, Denmark. The measurements are performed within a wide range of atmospheric stability conditions, which allows a comparison of the models with the average wind profile computed in seven stability classes, showing a better agreement than compared to the traditional surface-layer wind profile. The wind profile is measured by combining cup anemometer and lidar observations, showing good agreement at the overlapping heights. The height of the boundary layer, a parameter required for the wind profile models, is estimated under neutral and stable conditions using surface-layer turbulence measurements, and under unstable conditions based on the aerosol backscatter profile from ceilometer observations.     

Zur Stratigraphie des Altpaläozoikums in Argentinien

At the beginning of the Paleozoic era three geotectonic units were already constitued in the argentine territory: 1. central cratonic region; 2. ortogeosynclinal belt in the West, and 3. intracratonic region in the East. On the basis of the morphostructural units that emerge out of the development of the geotectonic pattern, the regional distribution and stratigraphy of the Lower Paleozoic rocks are described (Cambrian to Silurian). In the Northern Argentina (Subandine ranges, Eastern Cordillera and Puna) the stratigraphical sequence is complete with a thickness of 9.100 meters. In the Transpampean Ranges only the Ordovician (Tremadoc-Llanvirn) is represented with a minimum thickness of 3.850 meters. In the Precordillera of Western Argentina the sequence is complete with a minimum thickness of 6.000 meters, the Ordovician being the most developed. In the San Rafael ranges (Mendoza), the Northern and Southern ranges of the Buenos Aires province, the Northpatagonian nesocraton and the Chaco-Parana basin, the succession is incomplete or little known. In each case the recognized lithological units are described and their respective stratigraphical relations are indicated.     

Geological and morphological study of the Jiufengershan landslide triggered by the Chi-Chi Taiwan earthquake

The Jiufengershan rock and soil avalanche is one of the largest landslides triggered by the Chi-Chi earthquake Taiwan 1999. The landslide destabilized the western limb of the Taanshan syncline along a weak stratigraphic layer. It involved a flatiron remnant, which was almost entirely mobilized during the earthquake. The avalanche was slowed down by NS trending ridges located downstream along the Jiutsaihu creek. The landslide affected a 60 m thick and 1.5 km long sedimentary pile composed of shales and sandstones, which dip 22°SE toward a transverse valley. The triggering mechanism and the sliding process were analyzed by means of geological and morphological data from aerial photographs and observed in the field. A high-resolution airborne Light Detection and Ranging (LiDAR) image taken 2.5 years after the landslide allows the identification of morphological structures along the sliding surface and the landslide accumulation. The sliding surface shows several deformation structures such as fault scarps and folds. These structures are interpreted in terms of basal shear stresses created during the avalanche. Three major joint sets were identified at the sliding surface. The isopach map of the landslide was calculated from the comparison between elevation models before and after the earthquake. The coseismic volume of mobilized material and landslide deposit data are 42 × 10⁶ m³ and 50 × 10⁶ m³, respectively. The geometry of the landslide accumulation in the field has an irregular star shape. The morphology of the deposit area shows a sequence of smooth reliefs and depressions that contrast with the neighboring ridges.     

Status of an endangered subspecies: the peninsular pronghorn at Baja California

During November 1993, we traversed by ground and by air the Vizcaíno Desert, the last redoubt of the peninsular pronghorn (Antilocapra americana peninsularis). A total of 29 h of aerial census was performed and a total of 1900 km²were covered by ground, totalling 400 man hours of survey. At present the peninsular pronghorn population consists of 175 individuals, and inhabits an area of approximately 5000 km². Because of the impossibility of controlling its activities over such an area and because of the present small population size, we propose to manage part of the population in semi-captivity at Mesa de la Choya island, with the objective of assuring the survival of this subspecies, the most endangered mammal in Mexico.