Cold gas accretion in galaxies     

Renzo Sancisi  Filippo Fraternali  Tom Oosterloo  Thijs van der Hulst 《Astronomy and Astrophysics Review》2008,15(3):189-223

Evidence for the accretion of cold gas in galaxies has been rapidly accumulating in the past years. HI observations of galaxies and their environment have brought to light new facts and phenomena which are evidence of ongoing or recent accretion: (1) A large number of galaxies are accompanied by gas-rich dwarfs or are surrounded by HI cloud complexes, tails and filaments. This suggests ongoing minor mergers and recent arrival of external gas. It may be regarded, therefore, as direct evidence of cold gas accretion in the local universe. It is probably the same kind of phenomenon of material infall as the stellar streams observed in the halos of our galaxy and M 31. (2) Considerable amounts of extra-planar HI have been found in nearby spiral galaxies. While a large fraction of this gas is undoubtedly produced by galactic fountains, it is likely that a part of it is of extragalactic origin. Also the Milky Way has extra-planar gas complexes: the Intermediate- and High-Velocity Clouds (IVCs and HVCs). (3) Spirals are known to have extended and warped outer layers of HI. It is not clear how these have formed, and how and for how long the warps can be sustained. Gas infall has been proposed as the origin. (4) The majority of galactic disks are lopsided in their morphology as well as in their kinematics. Also here recent accretion has been advocated as a possible cause. In our view, accretion takes place both through the arrival and merging of gas-rich satellites and through gas infall from the intergalactic medium (IGM). The new gas could be added to the halo or be deposited in the outer parts of galaxies and form reservoirs for replenishing the inner parts and feeding star formation. The infall may have observable effects on the disk such as bursts of star formation and lopsidedness. We infer a mean “visible” accretion rate of cold gas in galaxies of at least . In order to reach the accretion rates needed to sustain the observed star formation (), additional infall of large amounts of gas from the IGM seems to be required.  相似文献   

Detection of Hazardous Cavities Below a Road Using Combined Geophysical Methods   总被引：1，自引：0，他引：1  

L. De Giorgi  G. Leucci 《Surveys in Geophysics》2014,35(4):1003-1021

Assessment of the risk arising from near-surface natural hazard is a crucial step in safeguarding the security of the roads in karst areas. It helps authorities and other related parties to apply suitable procedures for ground treatment, mitigate potential natural hazards and minimize human and economic losses. Karstic terrains in the Salento Peninsula (Apulia region—South Italy) is a major challenge to engineering constructions and roads due to extensive occurrence of cavities and/or sinkholes that cause ground subsidence and both roads and building collapse. Cavities are air/sediment-filled underground voids, commonly developed in calcarenite sedimentary rocks by the infiltration of rainwater into the ground, opening up, over a long period of time, holes and tunnels. Mitigation of natural hazards can best be achieved through careful geoscientific studies. Traditionally, engineers use destructive probing techniques for the detection of cavities across regular grids or random distances. Such probing is insufficient on its own to provide confidence that cavities will not be encountered. Frequency of probing and depth of investigation may become more expensive. Besides, probing is intrusive, non-continuous, slow, expensive and cannot provide a complete lateral picture of the subsurface geology. Near-surface cavities usually can be easily detected by surface geophysical methods. Traditional and recently developed measuring techniques in seismic, geoelectrics and georadar are suitable for economical investigation of hazardous, potentially collapsing cavities. The presented research focused on an integrated geophysical survey that was carried out in a near-coast road located at Porto Cesareo, a small village a few kilometers south west of Lecce (south Italy). The roads in this area are intensively affected by dangerous surface cracks that cause structural instability. The survey aimed to image the shallow subsurface structures, including karstic features, and evaluate their extent, as they may cause rock instability and lead to cracking of the road. Seismic refraction tomography and ground-penetrating radar surveys were carried out along several parallel traverses extending about 100 m on the cracked road. The acquired data were processed and interpreted integrally to elucidate the shallow structural setting of the site. Integrated interpretation led to the delineation of hazard zones rich with karstic features in the area. Most of these karstic features are associated with vertical and subvertical linear features and cavities. These features are the main reason of the rock instability that resulted in potentially dangerous cracking of road.  相似文献   

An analysis of global model projections over Italy, with particular attention to the Italian Greater Alpine Region (GAR)   总被引：1，自引：1，他引：0  

Paola Faggian  Filippo Giorgi 《Climatic change》2009,96(1-2):239-258

This study surveys the most recent projections of future climate change provided by 20 Atmospheric-Ocean General Circulation Models (AOGCMs) participating in the Coupled Model Intercomparison Project 3 (CMIP3) with focus on the Italian region and in particular on the Italian Greater Alpine Region (GAR). We analyze historical and future simulations of monthly-mean surface air temperature (T) and total precipitation (P). We first compare simulated T and P from the AOGCMs with observations over Italy for the period 1951–2000, using bias indices as a metric for estimating the performance of each model. Using these bias indices and different ensemble averaging methods, we construct ensemble mean projections of future climate change over these regions under three different IPCC emission scenarios (A2, A1B, and B1). We find that the emissions pathway chosen has a greater impact on future simulated climate than the criteria used to obtain the ensemble means. Across all averaging methods and emission scenarios, the models project annual mean increase in T of 2–4°C over the period 1990–2100, with more pronounced increases in summer and warming of similar magnitude at high and low elevations areas (according to a threshold of 400 m). The models project decreases in annual-mean P over this same time period both over the Italian and GAR regions. This decrease is more pronounced over Italy, since a small increase in precipitation over the GAR is projected in the winter season.  相似文献   

A daily temperature dataset over China and its application in validating a RCM simulation   总被引：36，自引：0，他引：36  

徐影  高学杰  沈艳  许崇海  石英 《大气科学进展》2009,26(4):763-772

This paper describes the construction of a 0.5°×0.5°daily temperature dataset for the period of 1961- 2005 over mainland China for the purpose of climate model validation. The dataset is based on the in- terpolation from 751 observing stations in China and comprises 3 variables: daily mean,minimum,and maximum temperature.The"anomaly approach"is applied in the interpolation.The gridded climatology of 1971-2000 is first calculated and then a gridded daily anomaly for 1961-2005 is added to the climatologY to o...  相似文献   

Regional variability of climate change hot-spots in East Asia   总被引：2，自引：0，他引：2  

徐影  高学杰 《大气科学进展》2009,26(4):783-792

The regional climate change index (RCCI) is employed to investigate hot-spots under 21st century global warming over East Asia. The RCCI is calculated on a 1-degree resolution grid from the ensemble of CMIP3 simulations for the B1, A1B, and A2 IPCC emission scenarios. The RCCI over East Asia exhibits marked sub-regional variability. Five sub-regional hot-spots are identified over the area of investigation: three in the northern regions (Northeast China, Mongolia, and Northwest China), one in eastern China, and one over the Tibetan Plateau. Contributions from different factors to the RCCI are discussed for the sub-regions. Analysis of the temporal evolution of the hot-spots throughout the 21st century shows different speeds of response time to global warming for the different sub-regions. Hot-spots firstly emerge in Northwest China and Mongolia. The Northeast China hot-spot becomes evident by the mid of the 21st century and it is the most prominent by the end of the century. While hot-spots are generally evident in all the 5 sub-regions for the A1B and A2 scenarios, only the Tibetan Plateau and Northwest China hot-spots emerge in the B1 scenario, which has the lowest greenhouse gas (GHG) concentrations. Our analysis indicates that sub-regional hot-spots show a rather complex spatial and temporal dependency on the GHG concentration and on the different factors contributing to the RCCI.  相似文献   

Reply to comment on “Storm surge frequency reduction in Venice under climate change” by G. Jordà, D. Gomis & M. Marcos     

Alberto Troccoli  Filippo Zambon  Kevin I. Hodges  Marco Marani 《Climatic change》2012,113(3-4):1089-1095

  相似文献   

Indirect vs. Direct Effects of Anthropogenic Sulfate on the Climate of East Asia as Simulated with a Regional Coupled Climate-Chemistry/Aerosol Model   总被引：11，自引：0，他引：11  

Filippo Giorgi  Xungqiang Bi  Yun Qian 《Climatic change》2003,58(3):345-376

We intercompare a series of multi-year simulations with a coupled regionalchemistry-climate model for east Asia to assess the relative importance ofdirect and indirect (Type I) effects of anthropogenic sulfate on the climateof the region. Both direct and indirect aerosol effects induce a negativeradiative forcing that results in a cooling of the surface and in a decrease of precipitation. Under present day sulfur emissions,the direct aerosol effects prevail during the cold season, while the indirecteffects dominate in the warm season (when cloudiness is maximum over the region). When both the direct and indirect effects are included, the surface cooling varies in the range of –0.1 to over –1 K throughout the region and extended areas ofstatistically significant cooling are found in all seasons except winter.The indirect effects largely dominate in inhibiting precipitation, especiallyduring the summer. When doubling the sulfur emissions, the direct effects aresubstantially strengthened, while the indirect effects are only marginally affected. This indicates that the indirect effects over the region might be asymptotically approaching their maximum efficiency. Overall, the indirect effects appear necessary to explain theobserved temperature record over some regions of China, at least in the warm season.A number of uncertainties need to be addressed, such as due to Type IIindirect effects, modeling of the relationship between aerosol concentration and cloud optical properties, and contribution of aerosols other than anthropogenic sulfate.  相似文献   

Climate Scenarios for the Southeastern U.S. Based on GCM and Regional Model Simulations     

L. O. Mearns  F. Giorgi  L. McDaniel  C. Shields 《Climatic change》2003,60(1-2):7-35

We analyze the control runs and 2 × CO₂ projections (5-yearlengths) of the CSIRO Mk 2 GCM and the RegCM2 regional climate model, which was nested in the CSIRO GCM, over the Southeastern U.S.; and we present the development of climate scenarios for use in an integrated assessment of agriculture. The RegCM exhibits smaller biases in both maximum and minimum temperature compared to the CSIRO. Domain average precipitation biases are generally negative and relatively small in winter, spring, and fall, but both models produce large positive biases in summer, that of the RegCM being the larger. Spatial pattern correlations of the model control runs and observations show that the RegCM reproduces better than the CSIRO the spatial patterns of precipitation, minimum and maximum temperature in all seasons. Under climate change conditions, the most salient feature from the point of view of scenarios for agriculture is the large decreases in summer precipitation, about 20% in the CSIRO and 30% in the RegCM. Increases in springprecipitation are found in both models, about 35% in the CSIRO and 25% in theRegCM. Precipitation decreases of about 20% dominate in winter in the CSIRO,while a more complex pattern of increases and decreases is exhibited by the regional model. Temperature increases by 3 to 5 °C in the CSIRO, the higher values dominating in winter and spring. In the RegCM, temperature increases are much more spatially and temporally variable, ranging from 1 to 7 °C acrossall months and grids. In summer large increases (up to 7 °C) in maximum temperature are found in the northeastern part of the domain where maximum drying occurs.  相似文献   

Variability and trends of sub-continental scale surface climate in the twentieth century. Part I: observations   总被引：1，自引：0，他引：1  

F. Giorgi 《Climate Dynamics》2002,18(8):675-691

An analysis is presented of observed temperature and precipitation variability and trends throughout the twentieth century over 22 land regions of sub-continental scale. Summer, winter and annual data are examined using a range of variability measures. Statistically significant warming trends are found over the majority of regions. The trends have a magnitude of up to 2 K per century and are maximum over cold climate regions. Only a few precipitation trends are statistically significant. Regional temperature and precipitation show pronounced variability at scales from interannual to multidecadal, with maximum over cold climate regions. The interannual variability shows significant variations and trends throughout the century, the latter being mostly negative for precipitation and both positive and negative for temperature. Temperature and precipitation anomalies show a chaotic-type behavior in which the regional conditions oscillate around the long term mean trend and occasionally fall into long-lasting (up to 10 years or more) anomaly regimes. A generally modest temporal correlation is found between anomalies of different regions and between temperature and precipitation anomalies for the same region. This correlation is mostly positive for temperature in cases of adjacent regions or regions in the same latitude belts. Several cases of negative inter-regional precipitation anomaly correlation are found. The ENSO significantly affects the anomaly variability patterns over a number of regions, primarily in tropical areas, while the NAO significantly affects the variability over northern mid- and high-latitude regions of Europe and Asia.  相似文献   

A multi-disciplinary study of the 2002–03 Etna eruption: insights into a complex plumbing system     

Daniele Andronico  Stefano Branca  Sonia Calvari  Michael Burton  Tommaso Caltabiano  Rosa Anna Corsaro  Paola Del Carlo  Gaetano Garfì  Luigi Lodato  Lusia Miraglia  Filippo Murè  Marco Neri  Emilio Pecora  Massimo Pompilio  Guiseppe Salerno  Letizia Spampinato 《Bulletin of Volcanology》2005,67(4):314-330

The 2002–03 Mt Etna flank eruption began on 26 October 2002 and finished on 28 January 2003, after three months of continuous explosive activity and discontinuous lava flow output. The eruption involved the opening of eruptive fissures on the NE and S flanks of the volcano, with lava flow output and fire fountaining until 5 November. After this date, the eruption continued exclusively on the S flank, with continuous explosive activity and lava flows active between 13 November and 28 January 2003. Multi-disciplinary data collected during the eruption (petrology, analyses of ash components, gas geochemistry, field surveys, thermal mapping and structural surveys) allowed us to analyse the dynamics of the eruption. The eruption was triggered either by (i) accumulation and eventual ascent of magma from depth or (ii) depressurisation of the edifice due to spreading of the eastern flank of the volcano. The extraordinary explosivity makes the 2002–03 eruption a unique event in the last 300 years, comparable only with La Montagnola 1763 and the 2001 Lower Vents eruptions. A notable feature of the eruption was also the simultaneous effusion of lavas with different composition and emplacement features. Magma erupted from the NE fissure represented the partially degassed magma fraction normally residing within the central conduits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is typical of most Etnean eccentric eruptions. We believe that there is a high probability that Mount Etna has entered a new eruptive phase, with magma being supplied to a deep reservoir independent from the central conduit, that could periodically produce sufficient overpressure to propagate a dyke to the surface and generate further flank eruptions.Editorial responsibility: J. Donnelly-Nolan  相似文献