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  • Articles  (222)
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  • 1
    Electronic Resource
    Electronic Resource
    New scheme for solving the amplitude equations in the state-specific coupled cluster theory with complete active space reference for ground and excited states (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 8503-8513 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new scheme for solving the coupled cluster (CC) amplitude equations for ground and excited electronic states in the state-selective multireference (MR) CC method based on the complete active space (CAS) reference wave function (CASCC) is proposed. The CASCC wave function is generated using a single formal reference determinant, which is one of the CAS determinants, as the origin of the configuration expansion. Some single and double excitations from other CAS determinants may be triple, quadruple, and higher excitations from the reference determinant. We show that one may include the contribution from these higher excitations indirectly by modifying the coupled cluster amplitude equations corresponding to the single and double excitations. The modification involves including projections against the higher excitations in the equations for the singles and doubles. Test calculations for the ground and the first excited state of the H8-model system and for the singlet–triplet splitting of the CH2-biradical shows that the results improve with the use of the new scheme and become to the FCI benchmarks. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1318758
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  • 2
    Electronic Resource
    Electronic Resource
    CASCCD: Coupled-cluster method with double excitations and the CAS reference (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9258-9268 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new multireference coupled-cluster method which includes double excitations and is based on the complete active space (CAS) multiconfigurational reference wave function is proposed. By partitioning the CAS orbitals into active and nonactive sets a two-component, coupled-cluster wave function involving excitations into orbitals of the different sets was constructed. The first component includes all the CAS excitations and the second component, which has the exponential form, consists of double external and semi-external excitations. The coupled-cluster equations for the energy and for the amplitudes involved in the two components of the wave function were derived and illustrated using a diagrammatic formalism. Several numerical tests were performed, and the results demonstrate a very good performance of the method as compared to the full configuration interaction results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481547
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  • 3
    Electronic Resource
    Electronic Resource
    Interannual variability in water masses in the Greenland Sea and adjacent areas (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Polar research 20 (2001), S. 0 
    Details
    ISSN: 1751-8369
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geography , Geosciences
    Notes: Oceanographic data covering the period 1950–1998 are used to determine interannual variations in the convection intensity and water mass structure in the Greenland Sea and adjacent areas. Extremely cold winters throughout 1965–1970 assisted intensification of the water vertical exchange in the Greenland and Norwegian seas. As a result, cold and fresh Greenland Sea Deep Water (GSDW) production was extremely high in the central Greenland Sea while in the southern Norwegian Sea warm and salty water spread downwards. The recent rapid warming in the Greenland Sea Gyre interior from 1980 originates, we argue, from an increase in the Atlantic Water (AW) temperature due to the advection of warm waters into the region with the Return Atlantic Current. The negative water temperature and salinity trends in the upper 300 m layer of the Atlantic Water in the Norwegian Sea prevailed during 1950–1990, whereas during 1980–1990 the water temperature trends are indicative of warming of that layer. Observation series obtained onboard the Ocean Weather Ship Mike confirmed the existence of layers with advectiondriven high oxygen concentrations in intermediate and deep layers. The depth of oxygen maxima and the values of oceanographic parameters at this horizon can be regarded as indicators of the convection intensity in the Arctic domain. A simultaneous rise in NAO index and GSDW temperature points to a link between atmospheric and thermohaline circulation. Weakening in water exchange with the North Atlantic could be the reason for the Polar Water recirculation increase within the Nordic seas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1751-8369.2001.tb00057.x
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  • 4
    Electronic Resource
    Electronic Resource
    Thermal Remagnetization of SmCo〈sub〉5〈/sub〉 Permanent Magnets - Influence of Starting Temperature and Field Fluctuations (2001)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 373-376 (Aug. 2001), p. 417-420 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/05/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.373-376.417.pdf
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  • 5
    Electronic Resource
    Electronic Resource
    Invasion of the Caspian Sea by the Comb Jellyfish Mnemiopsis Leidyi (Ctenophora) (2000)
    Springer
    Biological invasions 2 (2000), S. 255-258 
    Details
    ISSN: 1573-1464
    Keywords: caspian sea ; black sea ; ctenophore ; mnemiopsis ; aurelia ; beroe ; butterfish ; caspian seal ; invasions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010098624728
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  • 6
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    Contribution of Convection-Induced Heat Flux to Winter Ice Decay in the Western Nansen Basin (2018)
    American Geophysical Union
    In:  EPIC3Journal of Geophysical Research: Oceans, American Geophysical Union, ISSN: 2169-9275
    Details
    Publication Date: 2018-09-20
    Description: Gradually decaying Arctic sea ice changes the boundary conditions at the surface, separating ocean and atmosphere. In recent years, substantial reductions in sea ice during winter have been observed in the Atlantic sector of the Arctic Ocean, which forms the gateway for warm water inflow from the midlatitudes. In this study, we used routine output from the Mercator Ocean global operational system (MOGOS) to assess the efficiency of winter thermohaline convection transporting heat from deep layers to the ocean surface along the Atlantic origin water (AW) pathway, between Svalbard and Franz Joseph Land in the Nansen Basin. Positive temperature extremes in the AW layer in midwinter promote favorable prerequisite conditions for deep‐reaching thermohaline convection, with explicit signs captured by the MOGOS. Balance equations with several assumptions for the compact region around the position (81.30°N, 31°E) of the long‐term (2004–2010) mooring demonstrated that winter heat loss at the ocean surface is mainly compensated by convective heat flux from the AW layer. Heat and salt fluxes, associated with horizontal advection, are compatible with convective fluxes, while contribution of ice formation/melt is substantially smaller. Conclusion about the dominant role of vertical convection in shaping thermohaline structure and reducing sea ice in winter is supported by correlation analysis of the MOGOS output and mooring‐based measurements. Unfavorable background conditions (thick and consolidated sea ice in combination with specific directions of ice drift) may significantly alter convection development, as demonstrated for two sequential years with substantially different external forcing.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
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    Atlantic water flow into the Arctic Ocean through the St. Anna Trough in the northern Kara Sea (2015)
    In:  EPIC3JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 120(7), pp. 5158-5178
    Details
    Publication Date: 2015-12-02
    Description: The Atlantic Water flow from the Barents and Kara seas to the Arctic Ocean through the St. Anna Trough (SAT) is conditioned by interaction between Fram Strait branch water circulating in the SAT and Barents Sea branch water—both of Atlantic origin. Here we present data from an oceanographic mooring deployed on the eastern flank of the SAT from September 2009 to September 2010 as well as CTD (conductivity-temperature-depth) sections across the SAT. A distinct vertical density front over the SAT eastern slope deeper than ∼50 m is attributed to the outflow of Barents Sea branch water to the Arctic Ocean. In turn, the Barents Sea branch water flow to the Arctic Ocean is conditioned by two water masses defined by relative low and high fractions of the Atlantic Water. They are also traceable in the Nansen Basin downstream of the SAT entrance. A persistent northward current was recorded in the subsurface layer along the SAT eastern slope with a mean velocity of 18 cm s−1 at 134–218 m and 23 cm s−1 at 376–468 m. Observations and modeling suggest that the SAT flow has a significant density-driven component. It is therefore expected to respond to changes in the cross-trough density gradient conditioned by interaction between the Fram Strait and Barents Sea branches. Further modeling efforts are necessary to investigate hydrodynamic instability and eddy generation caused by the interaction between the SAT flow and the Arctic Ocean Fram Strait branch water boundary current.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    Greater role for Atlantic inflows on sea-ice loss in the Eurasian Basin of the Arctic Ocean (2017)
    In:  EPIC3Science, 356(6335), pp. 285-291, ISSN: 0036-8075
    Details
    Publication Date: 2017-06-15
    Description: Arctic sea-ice loss is a leading indicator of climate change and can be attributed, in large part, to atmospheric forcing. Here, we show that recent ice reductions, weakening of the halocline, and shoaling of the intermediate-depth Atlantic Water layer in the eastern Eurasian Basin have increased winter ventilation in the ocean interior, making this region structurally similar to that of the western Eurasian Basin. The associated enhanced release of oceanic heat has reduced winter sea-ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing, thus explaining the recent reduction in sea-ice cover in the eastern Eurasian Basin. This encroaching "atlantification" of the Eurasian Basin represents an essential step toward a new Arctic climate state, with a substantially greater role for Atlantic inflows.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 9
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    Arctic Ocean warming contributes to reduced polar ice cap (2011)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 40 (2010): 2743–2756, doi:10.1175/2010JPO4339.1.
    Description: Analysis of modern and historical observations demonstrates that the temperature of the intermediate-depth (150–900 m) Atlantic water (AW) of the Arctic Ocean has increased in recent decades. The AW warming has been uneven in time; a local 1°C maximum was observed in the mid-1990s, followed by an intervening minimum and an additional warming that culminated in 2007 with temperatures higher than in the 1990s by 0.24°C. Relative to climatology from all data prior to 1999, the most extreme 2007 temperature anomalies of up to 1°C and higher were observed in the Eurasian and Makarov Basins. The AW warming was associated with a substantial (up to 75–90 m) shoaling of the upper AW boundary in the central Arctic Ocean and weakening of the Eurasian Basin upper-ocean stratification. Taken together, these observations suggest that the changes in the Eurasian Basin facilitated greater upward transfer of AW heat to the ocean surface layer. Available limited observations and results from a 1D ocean column model support this surmised upward spread of AW heat through the Eurasian Basin halocline. Experiments with a 3D coupled ice–ocean model in turn suggest a loss of 28–35 cm of ice thickness after 50 yr in response to the 0.5 W m−2 increase in AW ocean heat flux suggested by the 1D model. This amount of thinning is comparable to the 29 cm of ice thickness loss due to local atmospheric thermodynamic forcing estimated from observations of fast-ice thickness decline. The implication is that AW warming helped precondition the polar ice cap for the extreme ice loss observed in recent years.
    Description: This study was supported by JAMSTEC (IP and VI), NOAA (IP, VI, and ID), NSF (IP,VA,VI, ID, JT, andMS),NASA(IP andVI), BMBF (ID), and UK NERC (SB) grants.
    Keywords: Arctic ; Forcing ; Temperature ; Sea ice ; Heating ; Coupled models
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 10
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    Greater role for Atlantic inflows on sea-ice loss in the Eurasian Basin of the Arctic Ocean (2017)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Science 356 (2017): 285-291, doi:10.1126/science.aai8204.
    Description: Arctic sea-ice loss is a leading indicator of climate change and can be attributed, in large part, to atmospheric forcing. Here we show that recent ice reductions, weakening of the halocline, and shoaling of intermediate-depth Atlantic Water layer in the eastern Eurasian Basin have increased winter ventilation in the ocean interior, making this region structurally similar to that of the western Eurasian Basin. The associated enhanced release of oceanic heat has reduced winter sea-ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing, thus explaining the recent reduction in sea-ice cover in the eastern Eurasian Basin. This encroaching “atlantification” of the Eurasian Basin represents an essential step toward a new Arctic climate state, with a substantially greater role for Atlantic inflows.
    Description: This study was supported by NSF grants #1203473 and #1249133 (AP, IP, MA, RR, VI), NOAA grant # NA15OAR4310155 (AP, IP, MA, RR, TB, VI) and by the A-TWAIN project, funded by the Arctic Ocean program at the FRAM-High North Research Centre for Climate and the Environment.
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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