Influence of the intraseasonal variability on heat waves in subtropical South America   总被引：1，自引：1，他引：0  

S. B. Cerne  C. S. Vera 《Climate Dynamics》2011,36(11-12):2265-2277

The influence of the intraseasonal variability on heat wave development over subtropical South America during austral summer is analyzed. The role of the South Atlantic Convergence Zone (SACZ) on this development is documented. Results show that intraseasonal variability can explain on average at least 32% of summer temperature variance. Moreover, 73% of the heat waves in subtropical South America develop in association with an active SACZ. The analysis of pentad maps shows that warm conditions in the region under study develop in association with the strengthening of an anticyclonic anomaly, which is discernible over the subtropical regions at least 15?days before temperature peak occurrence. That circulation anomaly is embedded in a large-scale Rossby wave train extending along the South Pacific Ocean that is linked to convection anomalies at the equatorial western and central Pacific Ocean. In addition, the development of the anticyclonic circulation over subtropical South America appears to be strengthened by the subsidence conditions promoted by the active SACZ, which result in temperature rise in the subtropical region under relatively dry conditions. On the other hand, during the last 2?days of evolution, SACZ activity weakens and the progressive temperature rise in the region is dominated by warmer and moister air being anomalously advected from the north. Results confirm the important role that SACZ activity on intraseasonal time scales has in inducing persistent circulation anomalies at the subtropical regions that can result in the development of persistent heat waves, and very extreme daily temperature.  相似文献   

Assessing risk associated with sea-level rise and storm surge��Redux     

Christine C. Shepard  Vera N. Agostini  Ben Gilmer  Tashya Allen  Jeff Stone  William Brooks  Michael W. Beck 《Natural Hazards》2013,65(1):375-376

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On the periodic solutions of a rigid dumbbell satellite in a circular orbit     

Juan L. G. Guirao  Juan A. Vera  Bruce A. Wade 《Astrophysics and Space Science》2013,346(2):437-442

The aim of the present paper is to provide sufficient conditions for the existence of periodic solutions of the perturbed attitude dynamics of a rigid dumbbell satellite in a circular orbit.  相似文献   

Optimizing the detection of carotene in cyanobacteria in a martian regolith analogue with a Raman spectrometer for the ExoMars mission     

U. Böttger  J.-P. de Vera  J. Fritz  I. Weber  H.-W. Hübers  D. Schulze-Makuch 《Planetary and Space Science》2012,60(1):356-362

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Storm influence on SPM concentrations in a coastal turbidity maximum area with high anthropogenic impact (southern North Sea)     

Michael Fettweis  Frederic Francken  Dries Van den Eynde  Toon Verwaest  Job Janssens  Vera Van Lancker 《Continental Shelf Research》2010

Multi-sensor tripod measurements in the high-turbidity area of the Belgian nearshore zone (southern North Sea) allowed investigating storm effects on near bed suspended particulate matter (SPM) concentrations. The data have shown that during or after a storm the SPM concentration increases significantly and that high concentrated mud suspensions (HCMS) are formed. Under these conditions, about 3 times more mass of SPM was observed in the water column, as compared to calm weather conditions. The following different sources of fine-grained sediments, influencing the SPM concentration signal, have been investigated: wind direction and the advection of water masses; the previous history and occurrence of fluffy layers; freshly deposited mud near the disposal grounds of dredged material, navigation channels and adjacent areas; and the erosion of medium-consolidated mud of Holocene age.  相似文献   

Tracing the influence of sewage discharge on coastal bays of Southern Vancouver Island (BC,Canada) using sedimentary records of phytoplankton     

Alanna Krepakevich  Vera Pospelova 《Continental Shelf Research》2010

The impact of sewage and stormwater effluents on phytoplankton is investigated by comparing organic-walled dinoflagellate cyst abundance and diversity from 38 surface sediment samples, flanking southern Vancouver Island. Site locations include those directly adjacent to wastewater outfall at Clover and Macaulay Points and Saanich Peninsula, as well as from a variety of near-shore environments with differing tidal flow influences. Excellently preserved dinoflagellate cyst assemblages have been recovered and 36 cyst taxa were identified. Local assemblages are characterized by a high relative proportion (average 56%) of cysts produced by heterotrophic dinoflagellates, which is typical for regions of high primary production. Relative proportional increases of cysts from heterotrophic species with particular increases of Polykrikos kofoidii/schwartzii and Dubridinium species, known to reflect areas affected by eutrophication, occur directly adjacent to all three sewage outfalls, as well as in the more stagnant waters of Esquimalt and Victoria Harbours and at the mouth of Cadboro Bay. Further effects of an anthropogenic effluent can be seen in the relatively higher concentrations of organic carbon and the diatom production proxy, biogenic opal. Results from this study clearly indicate a much larger impact zone than predicted by a sewage effluent plume model or trends found in monitored benthic biota and sediment chemistry that evidence primary outfall affects <800 m eastward of Macaulay Point and about 200 m eastward of the Clover Point. Enhanced production of cysts from potentially toxic Alexandrium species is also observed near locations of sewage outfalls.  相似文献   

Did the 1999 earthquake swarm on Gakkel Ridge open a volcanic conduit? A detailed teleseismic data analysis     

Carsten Riedel  Vera Schlindwein 《Journal of Seismology》2010,14(3):505-522

In 1999, a seismic swarm of 237 teleseismically recorded events marked a submarine eruption along the Arctic Gakkel Ridge, later on also analyzed by sonar, bathymetric, hydrothermal, and local seismic studies. We relocated the swarm with the global location algorithm HYPOSAT and analyzed the waveforms of the stations closest to the events by cross-correlation. We find event locations scattered around 85°35^′ N and 85° E at the southern rift wall and inside the rift valley of the Gakkel Ridge. Waveforms of three highly correlating events indicate a volumetric moment tensor component and highly precise referenced double-difference arrival times lead us to believe that they occur at the same geographical position and mark the conduit located further southeast close to a chain of recently imaged volcanic cones. This result is supported by station residual anomalies in the direction of the potential conduit. Seismicity is focused at the crust–mantle boundary at 16–20 km depth, but ascending toward the potential conduit during the beginning of April 1999, indicating an opening of the vent.  相似文献   

Phytoplankton abundance, biomass and diversity within and between Pantanal wetland habitats     

Simone Jaqueline Cardoso  Fábio RolandSimoni Maria Loverde-Oliveira  Vera Lúcia de Moraes Huszar 《Limnologica》2012,42(3):235-241

During the high water season, the flooding reduces environmental heterogeneity in aquatic ecosystems of the Pantanal wetland. When the water level recedes, lakes and channels are formed as individual systems. Therefore, we expected the spatial heterogeneity during the low water phase resulting in changes on biological communities leading to high phytoplankton abundance, biomass and diversity within and between habitats. To test this hypothesis, we analyzed eight freshwater systems (five oxbow lakes, two channels, and the river) during the low water period. Phytoplankton biomass, abundance, diversity (alpha, beta, gamma) and diversity metrics as richness (species per sample), Shannon diversity (H′) and evenness were measured in all systems along with nutrient concentrations, zooplankton and bacteria abundances. We found 97 species as gamma diversity. The alpha diversity was unexpectedly low in comparison to most other South American floodplain systems (38 species in river, 24 in channels and 29 in lakes). Also, the systems are relatively similar in composition (beta diversity, 28%). Connectivity differences between systems highlighted differences in phytoplankton abundance and biomass (fresh weight) ranging from 1428 ind mL⁻¹ (river) to 3710 ind mL⁻¹ (lakes) and from 0.71 mg L⁻¹ (river) to 2.9 mg L⁻¹ (lakes), respectively. However, our results did not indicate significant differences in phytoplankton species richness between the systems during the low water. Our main conclusions are that local factors may be responsible for changes on phytoplankton community and the time of isolation during the low water phase was not sufficient to promote changes in phytoplankton diversity between the habitats.  相似文献   

Influence of substrate tectonic heritage on the evolution of composite volcanoes: Predicting sites of flank eruption, lateral collapse, and erosion     

Alessandro Tibaldi  Claudia Corazzato  Andrey Kozhurin  Alfredo F.M. Lagmay  Federico A. Pasquar  Vera V. Ponomareva  Derek Rust  Daniel Tormey  Luigina Vezzoli 《Global and Planetary Change》2008,61(3-4):151-174

This paper aims to aid understanding of the complicated interplay between construction and destruction of volcanoes, with an emphasis on the role of substrate tectonic heritage in controlling magma conduit geometry, lateral collapse, landslides, and preferential erosion pathways. The influence of basement structure on the development of six composite volcanoes located in different geodynamic/geological environments is described: Stromboli (Italy), in an island arc extensional tectonic setting, Ollagüe (Bolivia–Chile) in a cordilleran extensional setting, Kizimen (Russia) in a transtensional setting, Pinatubo (Philippines) in a transcurrent setting, Planchon (Chile) in a compressional cordilleran setting, and Mt. Etna (Italy) in a complex tectonic boundary setting. Analogue and numerical modelling results are used to enhance understanding of processes exemplified by these volcanic centres. We provide a comprehensive overview of this topic by considering a great deal of relevant, recently published studies and combine these with the presentation of new results, in order to contribute to the discussion on substrate tectonics and its control on volcano evolution. The results show that magma conduits in volcanic rift zones can be geometrically controlled by the regional tectonic stress field. Rift zones produce a lateral magma push that controls the direction of lateral collapse and can also trigger collapse. Once lateral collapse occurs, the resulting debuttressing produces a reorganization of the shallow-level magma migration pathways towards the collapse depression. Subsequent landslides and erosion tend to localize along rift zones. If a zone of weakness underlies a volcano, long-term creep can occur, deforming a large sector of the cone. This deformation can trigger landslides that propagate along the destabilized flank axis. In the absence of a rift zone, normal and transcurrent faults propagating from the substrate through the volcano can induce flank instability in directions respectively perpendicular and oblique to fault strike. This destabilization can evolve to lateral collapse with triggering mechanisms such as seismic activity or magmatic intrusion.  相似文献   

Steric and mass-induced Mediterranean sea level trends from 14 years of altimetry data   总被引：2，自引：2，他引：0  

Francisco Criado-Aldeanueva  Jorge Del Río Vera  Jesús García-Lafuente 《Global and Planetary Change》2008,60(3-4):563-575

Long-term series of almost 14 years of altimetry data (1992–2005) have been analysed along with Sea Surface Temperature (SST) and temperature and salinity profiles to investigate sea level trends over the Mediterranean Sea. Although sea level variations are mainly driven by the steric contribution, the mass-induced component plays some role in modulating its oscillation. A spatially averaged positive trend of 2.1 ± 0.6 mm/year has been observed, but a change in sign in 2001 seems to appear. Steric effects (mainly on thermal origin) account for  55% of sea level trend. Although Mediterranean Sea is a semi-enclosed basin, this value is comparable to that reported for the global ocean. Sea level rise is particularly important in the Levantine basin south of Crete with values up to 10 ± 1 mm/year. Other areas of sea level rise are localised throughout the Levantine basin and in the Adriatic and Alboran Seas, with more moderate values. Sea level drop areas are localised in the Algerian basin, between the Balearic Islands and the African coasts and, particularly, in the Ionian basin. In this area, negative trends as high as − 10 ± 0.8 mm/year are detected mainly due to the mass-induced contribution, which suggests decadal changes of surface circulation. The inferred sea level trends have been correlated with North Atlantic Oscillation (NAO) indices and a low but significant correlation has been detected between sea level in the Levantine and Balearic basins and NAO index.  相似文献