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Wyświetlanie 1-10 z 34
Tytuł:
A model-measurements comparison of atmospheric forcing and surface fluxes of the Baltic Sea
Autorzy:
Rudolph, C.
Lehmann, A.
Tematy:
coupled sea-ice-ocean model
surface flux
temperature
pressure
radiation flux
heat flux
air-sea interaction
Baltic Sea
wave radiation
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Wydawca:
Polska Akademia Nauk. Instytut Oceanologii PAN
Powiązania:
https://bibliotekanauki.pl/articles/48268.pdf  Link otwiera się w nowym oknie
Opis:
Observed basic meteorological quantities, heat and radiation fluxes from three different measurement stations in the Baltic Sea are compared with model data of the coupled sea-ice-ocean model BSIOM in order to evaluate the atmospheric forcing, corresponding surface fluxes and the sea surface response. Observational data weremade available from the BASIS winter campaigns in 1998 and 2001 as well as from the r/v ‘Alkor’ cruise in June 2001. Simulated fluxes were calculated from prescribed atmospheric forcing provided from the SMHI meteorological database and modelled sea surface temperatures. The comparison of these fluxes with observations demonstrates a strong correlation, even though mean differences in sensible heat fluxes range from 4 to 12 W m−2 in winter and −25 W m−2 in the June experiment. Differences in latent heat fluxes range from −10 to 23 W m−2. The short-wave radiation flux used as model forcing is on average 15 W m−2 less than the corresponding observations for the winter experiments and 40 W m−2 for the June experiment. Differences in net long-wave radiation fluxes range from −5 to 12W m−2 in winter and −62W m−2 for the June experiment. The correspondence between measured and calculated momentum fluxes is very high, which confirms the usability of our model component for calculating surface winds and wind stresses from the atmospheric surface pressure.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Dynamic features of successive upwelling events in the Baltic Sea - a numerical case study
Autorzy:
Myrberg, K.
Andrejev, O.
Lehmann, A.
Tematy:
Baltic Sea
Hel Peninsula
numerical modelling
coastal upwelling
thermal stratification
sea surface temperature
water column
Polish coast
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Wydawca:
Polska Akademia Nauk. Instytut Oceanologii PAN
Powiązania:
https://bibliotekanauki.pl/articles/48404.pdf  Link otwiera się w nowym oknie
Opis:
Coastal upwelling often reveals itself during the thermal stratification season as an abrupt sea surface temperature (SST) drop. Its intensity depends not only on the magnitude of an upwelling-favourable wind impulse but also on the temperature stratification of the water column during the initial stage of the event. When a ‘chain’ of upwelling events is taking place, one event may play a part in forming the initial stratification for the next one; consequently, SST may drop significantly even with a reduced wind impulse. Two upwelling events were simulated on the Polish coast in August 1996 using a three-dimensional, baroclinic prognostic model. The model results proved to be in good agreement with in situ observations and satellite data. Comparison of the simulated upwelling events show that the first one required a wind impulse of 28 000 kg m−1 s−1 to reach its mature, full form, whereas an impulse of only 7500 kg m−1 s−1 was sufficient to bring about a significant drop in SST at the end of the second event. In practical applications like operational modelling, the initial stratification conditions prior to an upwelling event should be described with care in order to be able to simulate the coming event with very good accuracy.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A statistical approach to coastal upwelling in the Baltic Sea based on the analysis of satellite data for 1990–2009
Autorzy:
Lehmann, A.
Myrberg, K.
Hoflich, K.
Tematy:
Baltic Sea
coastal upwelling
sea surface temperature
statistical analysis
numerical model
1990-2009 period
meteorological data
satellite data
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Wydawca:
Polska Akademia Nauk. Instytut Oceanologii PAN
Powiązania:
https://bibliotekanauki.pl/articles/49090.pdf  Link otwiera się w nowym oknie
Opis:
A statistical analysis of Baltic Sea upwelling has been carried out to cover, for the first time, the entire sea area for the period 1990–2009. Weekly composite SST maps based on NOAA/AVHRR satellite data were used to evaluate the location and frequency of upwelling. The results obtained were analysed and compared with earlier studies with excellent agreement. Our study enables the most intense upwelling areas in the entire Baltic Sea to be evaluated. According to the analysis of 443 SST maps, the most common upwelling regions are found off the Swedish south and east coasts (frequency 10–25%), the Swedish coast of the Bothnian Bay (16%), the southern tip of Gotland (up to 15%), and the Finnish coast of the Gulf of Finland (up to 15%). Pronounced upwelling also occurs off the Estonian coast and the Baltic east coast (up to 15%), the Polish coast and the west coast of Rugen (10–15%); otherwise the upwelling frequency was between 5 and 10%. Additionally, simulated SST distributions derived from a Baltic Sea numerical model were analysed for the same period. Furthermore, at specific positions close to the coastline, surface winds based on the SMHI meteorological data base were analysed for the same 20-year period. Wind components parallel to the coast were discriminated into favourable and unfavourable winds forcing upwelling. The obtained frequencies of upwelling-favourable winds fit very well the observed upwelling frequencies derived from satellite SST maps. A positive trend of upwelling frequencies along the Swedish east coast and the Finnish coast of the Gulf of Finland was calculated for the period 1990–2009.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Correlation analyses of Baltic Sea winter water mass formation and its impact on secondary and tertiary production
Autorzy:
Hinrichsen, H.H.
Lehmann, A.
Petereit, C.
Schmidt, J.
Tematy:
zooplankton
fish egg
development
thermal stratification
winter
water
Baltic Sea
mass formation
survival
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Wydawca:
Polska Akademia Nauk. Instytut Oceanologii PAN
Powiązania:
https://bibliotekanauki.pl/articles/47630.pdf  Link otwiera się w nowym oknie
Opis:
The thermal stratification of the upper water layers in the Baltic Sea varies seasonally in response to the annual cycle of solar heating and wind-induced mixing. In winter,the stratification down to the halocline is almost completely eroded by convection and strong wind mixing. Monthly averaged temperature profiles obtained from the ICES hydrographic database were used to study the long-term variability (1950 to 2005) of winter water mass formation in different deep basins of the Baltic Sea east of the island of Bornholm. Besides strong interannual variability of deep winter water temperatures,the last two decades show a positive trend (increase of 1–1.5◦C). Correlations of winter surface temperatures to temperatures of the winter water body located directly above or within the top of the halocline were strongly positive until the autumn months. Such a close coupling allows sea surface temperatures in winter to be used to forecast the seasonal development of the thermal signature in deeper layers with a high degree of confidence. The most significant impact of winter sea surface temperatures on the thermal signature in this depth range can be assigned to February/March. Stronger solar heating during spring and summer results in thermal stratification of the water column leading to a complete decoupling of surface and deep winter water temperatures. Based on laboratory experiments,temp erature-dependent relationships were utilised to analyse interannual variations of biological processes with special emphasis on the upper trophic levels (e.g.,stage-sp ecific developmental rates of zooplankton and survival rates of fish eggs).
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin and Charge Current in a Short Semiconducting Chain of Paramagnetic Ionic Blocks
Autorzy:
Lehmann-Szweykowska, A.
Wojciechowski, R.
Micnas, R.
Tematy:
72.25.Dc
73.61.Le
73.63.Rt
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1810512.pdf  Link otwiera się w nowym oknie
Opis:
We deal with the electric current flowing through a short chain of paramagnetic ionic blocks, coupled to metallic electrodes in the serial configuration. An original three-band Hubbard-Anderson Hamiltonian is diagonalised at the level of the single ionic block. A minimal but sufficient set of the latter's four hybridised eigenstates serves as a basis for the determination of the time-ordered temperature-dependent matrix Green functions, in terms of which all the current-voltage (I-V) characteristics can be expressed provided the coupling to the electrodes is weak. The separation of the opposite-spin contributions to the electric current and, consequently, the spin current from the left to right electrode can result from the on-site Coulomb repulsion term of Hubbard-Anderson Hamiltonian, with no spin polarisation at the electrodes, but with the Zeeman-like coupling of the centre to either a molecular or an external magnetic field.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Structural and Magnetic Properties of Co Thin Films on Au(111) Substrates
Autorzy:
Walczak, A.
Ślusarski, T.
Lehmann-Szweykowska, A.
Kamieniarz, G.
Tematy:
75.70.-i
68.35.-p
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1489873.pdf  Link otwiera się w nowym oknie
Opis:
The structural and magnetic properties of thin Co films grown on Au(111) substrates are investigated using ab initio local-spin-density calculations in the generalized gradient approximation. It is shown that a large lattice intermismatch between Co and Au(111) leads to a strong contraction of the interlayer distances within the Co layer, which adopts either the hexagonal close-packed (α-phase) or the face-centered cubic (β-phase) structure of bulk Co. Magnetic moments in the Co layer are increased beyond their value in bulk Co, the enhancement being strongest at the free surface and at the Co/Au interface, and more modest in the central part of the adlayer. Moderating influence of capping Ag layers on the structure and the magnetic properties of the films has also been considered. It is shown that Ag capping reduces the magnetic moments in comparison to uncovered Co/Au systems.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Energy Spectrum of Single-Hole States in Transition Metal Oxides
Autorzy:
Lehmann-Szweykowska, A.
Wojciechowski, R. J.
Gehring, G. A.
Tematy:
71.10.Fd
72.20.-i
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/2013222.pdf  Link otwiera się w nowym oknie
Opis:
The p-d hybridised single-hole states of the transition-metal-oxygen tetrahedron (TMO$\text{}_{4}$) are collectivised due to the direct p-p hopping between oxygens of different clusters. The lowest-lying energy band is always narrow and fully occupied. The first excited band gets occupied as an effect of valence-uncompensated doping, so it can be almost localised. The possible hole excitations to the two higher energy bands, which are wider, may imply the Mott-like hopping form of charge transport in these systems.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Properties of the Semi Spin Glass Ground State of Garnets
Autorzy:
Koper, A.
Lehmann-Szweykowska, A.
Thomas, M.
Wojciechowski, R. J.
Tematy:
75.10.Hk
75.50.Bb
81.30.Bx
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1861316.pdf  Link otwiera się w nowym oknie
Opis:
A strong magnetic ordering response to valence-uncompensated doping observed experimentally in yttrium iron garnet, indicates the importance of a thorough analysis of the problem. Within the framework of the classical two-sublattice Heisenberg model the position on the ground state phase diagram, corresponding to the experimentally found values of the superexchange parameters of yttrium iron garnet, turns out to lie close to the semi spin glass region. Thus, in this paper, the magnetic structure factor, the spectrum of magnetic excitations, the density of states and a magnetic contribution to the specific heat, are calculated and discussed.
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-10 z 34

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