Sensitivity of transient climate change to tidal mixing: Southern Ocean heat uptake in climate change experiments performed with ECHAM5/MPIOM     

E. Exarchou  J.-S. von Storch  J. H. Jungclaus 《Climate Dynamics》2014,42(7-8):1755-1773

We investigate the sensitivity of the transient climate change to a tidal mixing scheme. The scheme parameterizes diapycnal diffusivity depending on the location of energy dissipation over rough topography, whereas the standard configuration uses horizontally constant diffusivity. We perform ensemble climate change experiments with two setups of MPIOM/ECHAM5, one setup with the tidal mixing scheme and the second setup with the standard configuration. Analysis of the responses of the transient climate change to CO₂ increase reveals that the implementation of tidal mixing leads to a significant reduction of the transient surface warming by 9 %. The weaker surface warming in the tidal run is localized particularly over the Weddell Sea, likely caused by a stronger ocean heat uptake in the Southern Ocean. The analysis of the ocean heat budget reveals that the ocean heat uptake in both experiments is caused by changes in convection and advection. In the upper ocean, heat uptake is caused by reduced convection and enhancement of the Deacon Cell, which appears also in isopycnal coordinates. In the deeper ocean, heat uptake is caused by reduction of convective cooling associated with the circulation polewards of 65°S. Tidal mixing leads to stronger heat uptake in the Southern Ocean by causing stronger changes in advection, namely a stronger increase in the Deacon Cell and a stronger reduction in advective cooling by the circulation polewards of 65°S. Counter-intuitively, the relation between tidal mixing and greater heat storage in the deep ocean is an indirect one, through the influence of tidal mixing on the circulation.  相似文献   

Polar Low genesis over the North Pacific under different global warming scenarios   总被引：1，自引：1，他引：0  

Fei Chen  Hans von Storch  Lili Zeng  Yan Du 《Climate Dynamics》2014,43(12):3449-3456

Following an earlier climatological study of North Pacific Polar Lows by employing dynamical downscaling of NCEP1 reanalysis in the regional climate model COSMO-CLM, the characteristics of Polar Low genesis over the North Pacific under different global warming scenarios are investigated. Simulations based on three scenarios from the Special Report on Emissions Scenarios were conducted using a global climate model (ECHAM5) and used to examine systematic changes in the occurrence of Polar Lows over the twenty first century. The results show that with more greenhouse gas emissions, global air temperature would rise, and the frequency of Polar Lows would decrease. With sea ice melting, the distribution of Polar Low genesis shows a northward shift. In the scenarios with stronger warming there is a larger reduction in the number of Polar Lows.  相似文献   

Chemistry of the heavily urbanized Bagmati River system in Kathmandu Valley, Nepal: export of organic matter, nutrients, major ions, silica, and metals     

Maya P. Bhatt  William H. McDowell  Kevin H. Gardner  Jens Hartmann 《Environmental Earth Sciences》2014,71(2):911-922

Water quality in less-developed countries is often subject to substantial degradation, but is rarely studied in a systematic way. The concentration and flux of major ions, carbon, nitrogen, silicon, and trace metals in the heavily urbanized Bagmati River within Kathmandu Valley, Nepal, are reported. The concentrations of all chemical species increased with distance downstream with the exceptions of protons and nitrate, and showed strong relationships with population density adjacent to the river. Total dissolved nitrogen (TDN), dominated by NH₄, was found in high concentrations along the Bagmati drainage system. The export of dissolved organic carbon (DOC) and TDN were 23 and 33 tons km^?2 year^?1, respectively, at the outlet point of the Kathmandu Valley, much higher than in relatively undeveloped watersheds. The cationic and silica fluxes were 106 and 18 tons km^?2 year^?1 at the outlet of the Bagmati within Kathmandu Valley, and 36 and 32 tons km^?2 year^?1 from the relatively pristine headwater area. The difference between headwaters and the urban site suggests that the apparent weathering flux is three times higher than the actual weathering rate in the heavily urbanized Bagmati basin. Fluxes of cations and silica are above the world average, as well as fluxes from densely populated North American and European watersheds. End-member composition of anthropogenic sources like sewage or agricultural runoff is needed to understand the drivers of this high rate of apparent weathering.  相似文献   

Anthropogenic influence of trace metals in sediments of the Al-Qilt catchment,West Bank,Palestine: 1. Contamination factor and bonding forms     

Sobhi Samhan  Kurt Friese  Wolf von Tümpling  Herbert Pöllmann  Heinz Hoetzl  Marwan Ghanem 《Environmental Earth Sciences》2014,71(4):1533-1539

Al-Qilt catchment, located east of both the Ramallah and Jerusalem districts is strongly influenced by waste waters discharged from Israeli settlements and Palestinian urban centers. In this research, our aim was to verify the chemical status of the surface sediments from the Al-Qilt catchment during 2008/2009. For this purpose, 36 surface sediment samples were collected and analyzed with ICP/MS within the fraction of below 63 μm. The extent of contamination of trace metals from Al-Qilt sediments sites were measured by evaluating the contamination factors (CF) from digestion by aqua regia and additionally by sequential extraction steps using the BCR-method. On the basis of the calculated CF, sediments appear particularly contaminated with Zn, Cu, Ag, Sn, Cd, Hg, Bi, and B. Three regions, Wadi Sweanit, Ras Al-Qilt, and Qalandiah have been identified as critical points of contamination. Trace metal inputs to the Al-Qilt catchment need to be kept under strict control in the future since Ras Al-Qilt is considered as one of the important springs in the area and is used for domestic purposes. Moreover, it will be susceptible to pollution if no action is taken to decrease the pollution at the upstream of Al-Qilt.  相似文献   

Boundary layer ion composition at Jupiter during the inbound pass of the Ulysses flyby     

A.B. Galvin  C.M.S. Cohen  F.M. Ipavich  R. von Steiger  J. Woch  U. Mall 《Planetary and Space Science》1993,41(11-12)

During the inbound segment of the Ulysses flyby of Jupiter, there were multiple incursions into the dawnside low-latitude boundary layer, as identified by Bame et al. (Science257, 1539–1542, 1992) using plasma electron data. In the present study, ion composition and spectral measurements provide independent collaborative evidence for the existence of distinct boundary layer regions. Measurements are taken in the energy-per-charge range of 0.6–60 keV/e and involve mass as well as mass-per-charge identification by the Ulysses/SWICS experiment. Ion species of Jovian magnetospheric origin (including O⁺, O²⁺, S²⁺, S³⁺) and sheath origin (including He²⁺ and high charge state CNO) have been directly identified for the first time in the Jovian magnetospheric boundary layer. Protons of probably mixed origin and He⁺ of possibly sheath (ultimately interstellar pickup) origin were also observed in the boundary layer. Sheath-like ions are observed throughout the boundary layer; however, the Jovian ions are depleted or absent for portions of two boundary layer cases studied. Ions of solar wind origin are observed within the outer magnetosphere. and ions of magnetospheric origin are found within the sheath, indicating that transport across the magnetopause boundary can work both ways, at least under some conditions. Although their source cannot be uniquely identified, the proton energy spectrum in the boundary layer suggests a sheath origin for the lower energy protons.  相似文献   

Turbulence in Class 0 and I protostellar envelopes     

D. Ward-Thompson  L. Hartmann  D. J. Nutter 《Monthly notices of the Royal Astronomical Society》2005,357(2):687-690

We estimate the levels of turbulence in the envelopes of class 0 and I protostars using a model based on measurements of the peak separation of double-peaked asymmetric line profiles. We use observations of 20 protostars of both class 0 and I taken in the  HCO⁺(J = 3 → 2)  line that show the classic double-peaked profile. We find that some class 0 sources show high levels of turbulence, whilst others demonstrate much lower levels. In class I protostars, we find predominantly low levels of turbulence. The observations are consistent with a scenario in which class 0 protostars form in a variety of environments and subsequently evolve into class I protostars. The data do not appear to be consistent with a recently proposed scenario in which class 0 protostars can only form in extreme environments.  相似文献   

Assessing the Completeness of Bicycle Trail and Lane Features in OpenStreetMap for the United States   总被引：1，自引：0，他引：1       下载免费PDF全文

Hartwig H. Hochmair  Dennis Zielstra  Pascal Neis 《Transactions in GIS》2015,19(1):63-81

This article assesses the completeness of bicycle trail and on‐street lane features in OpenStreetMap (OSM). Comparing OSM cycling features with reference data from local planning agencies for selected US Urbanized Areas shows that OSM bicycle trails tend to be more completely mapped than bicycle lanes. Manual evaluation of mapped cycling features in OSM and Google Maps for selected test areas within the Central Business Districts of Portland (OR) and Miami (FL) through comparison with governmental datasets, satellite imagery, and Google Street View, shows that the Bicycle layer in Google Maps can help to identify some missing or erroneously mapped OSM cycling links. However, Google Maps was also found to have some gaps in its data layers, suggesting that consultation of current trail and lane data from local planning authorities, if available, should be considered as an additional data source for bicycle related planning projects.  相似文献   

Zircon geochronology and geochemistry to constrain the youngest eruption events and magma evolution of the Mid-Miocene ignimbrite flare-up in the Pannonian Basin,eastern central Europe     

Réka?LukácsEmail author  Szabolcs?Harangi  Olivier?Bachmann  Marcel?Guillong  Martin?Dani?ík  Yannick?Buret  Albrecht?von?Quadt  István?Dunkl  László?Fodor  Jakub?Sliwinski  Ildikó?Soós  János?Szepesi 《Contributions to Mineralogy and Petrology》2015,170(5-6):52

A silicic ignimbrite flare-up episode occurred in the Pannonian Basin during the Miocene, coeval with the syn-extensional period in the region. It produced important correlation horizons in the regional stratigraphy; however, they lacked precise and accurate geochronology. Here, we used U–Pb (LA-ICP-MS and ID-TIMS) and (U–Th)/He dating of zircons to determine the eruption ages of the youngest stage of this volcanic activity and constrain the longevity of the magma storage in crustal reservoirs. Reliability of the U–Pb data is supported by (U–Th)/He zircon dating and magnetostratigraphic constraints. We distinguish four eruptive phases from 15.9 ± 0.3 to 14.1 ± 0.3 Ma, each of which possibly includes multiple eruptive events. Among these, at least two large volume eruptions (>10 km³) occurred at 14.8 ± 0.3 Ma (Demjén ignimbrite) and 14.1 ± 0.3 Ma (Harsány ignimbrite). The in situ U–Pb zircon dating shows wide age ranges (up to 700 kyr) in most of the crystal-poor pyroclastic units, containing few to no xenocrysts, which implies efficient recycling of antecrysts. We propose that long-lived silicic magma reservoirs, mostly kept as high-crystallinity mushes, have existed in the Pannonian Basin during the 16–14 Ma period. Small but significant differences in zircon, bulk rock and glass shard composition among units suggest the presence of spatially separated reservoirs, sometimes existing contemporaneously. Our results also better constrain the time frame of the main tectonic events that occurred in the Northern Pannonian Basin: We refined the upper temporal boundary (15 Ma) of the youngest counterclockwise block rotation and the beginning of a new deformation phase, which structurally characterized the onset of the youngest volcanic and sedimentary phase.  相似文献   

Star Formation in Violent and Normal Evolutionary Phases     

Uta Fritze – von Alvensleben 《Astrophysics and Space Science》2002,281(1-2):379-382

Mergers of massive gas-rich galaxies trigger violent starbursts that - over timescales of > 100 Myr and regions > 10 kpc - form massive and compact star clusters comparable in mass and radii to Galactic globular clusters. The star formation efficiency is higher by 1–2 orders of magnitude in these bursts than in undisturbed spirals, irregulars or even BCDs. We ask the question if star formation in these extreme regimes is just a scaled-up version of the normal star formation mode of if the formation of globular clusters reveals fundamentally different conditions. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

I S L A An Astronomical World Space Observatory for The First Century of the 3 rd Millenium     

G.F.O. von Appen-Schnur  T. Luks 《Astrophysics and Space Science》1997,258(1-2):301-328

ISLA will be an astronomical observatory, operating at the upper limit of our planet Earth atmosphere, offering space like observing conditions in most aspects. ISLA can be maintained easily, modified easily if necessary, always kept at the state of the art and operated for very extended periods without polluting the stratosphere. ISLA is ideally suited to become the first world space observatory as the observing conditions are very much space-like – diffraction limited angular resolution, very low ambient temperature, remote control – however ISLA is easily accessible, telescopes and instruments can be continuously improved and ISLA's costs corresponds only to those of ground-based modern astronomical installations like the ESO-VLT-, KECK- and GEMINI-observatories. The cost of observing and experimenting on ISLA will be orders of magnitudes lower than those of building and operating any space telescope, allowing the astronomers of developing nations to participate in the ISLA observatory within their limited financial possibilities as competent and full partners. ISLA's 4-m and 2-m telescopes will operate diffraction limited from 0.3 μm in the optical, over the infrared, far-infrared to the sub-mm spectral range. ISLA's individual telescopes will permit imaging with 20 milli-arcsec spatial resolution in the optical, 5 times better than the Hubble Space Telescope. ISLA's telescopes can be combined to form an interferometer with a maximum baseline of 250 m with nearly complete coverage of the u,v plane. Interferometric resolution will be of the order of 20 micro-arcsec for the optical. ISLA will thus offer spatial resolution comparable or better than the intercontinental VLBI radio interferometers. ISLA's telescope efficiency will be many orders of magnitude better than comparable ground-based telescopes. The light collecting power of ISLA's interferometric telescopes will be orders of magnitudes greater than the future space interferometers under discussion. ISLA, being an aviation project and not a space project, can be realised in the typical time scale for the development of aviation: about 5 years. ISLA's cost for the whole observatory, including its movable ground station etc. will be of the order of a typical medium size ESA space mission. ISLA's lifetime will be in excess of many decades, as it can easily be maintained, modernised, repaired and improved. ISLA will become the origin of a new astronomical international organisation with worldwide participation. ISLA's telescopes will be of the greatest importance to all astronomical fields, as it will permit to study much fainter, much more distant objects with microscopic spatial resolution in wavelength regions inaccessible from ground. ISLA's many telescopes permit easily simultaneous observations at many wavelengths for rapidly varying objects, from continuously monitoring the surfaces of the planets in our solar system, surfaces of close-by stars, nuclei of galaxies to QSO's. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献