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  • 1. Bjork, Goran
    et al.
    Stranne, Christian
    Borenäs, Karin
    SMHI, Core Services.
    The Sensitivity of the Arctic Ocean Sea Ice Thickness and Its Dependence on the Surface Albedo Parameterization2013In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 26, no 4, p. 1355-1370Article in journal (Refereed)
    Abstract [en]

    In this study, the response of sea ice thickness to changes in the external forcing is investigated and particularly how this response depends on the surface albedo formulation by means of a one-dimensional coupled ocean-ice-atmosphere model. The main focus is on the thickness response to the atmospheric heat advection F-wall, solar radiation F-SW, and amount of snow precipitation S-prec. Different albedo parameterization schemes [ECHAM5, CSIRO, and Community Climate System Model, version 3 (CCSM3)] representing albedos commonly used in global climate models are compared together with more simplified schemes. Using different albedo schemes with the same external forcing produces large differences in ice thickness. The ice thickness response is similar for all realistic albedo schemes with a nearly linear decrease with increasing F-wall in the perennial ice regime and with a steplike transition into seasonal ice when F-wall exceeds a certain threshold. This transition occurs at an annual-mean ice thickness of 1.7-2.0 m. Latitudinal differences in solar insolation generally leads to increasing ice thickness toward the North Pole. The snow response varies significantly depending on which albedo scheme is used. The ECHAM5 scheme yields thinner ice with S-prec, the CSIRO scheme gives ice thickness nearly independent of S-prec, and with the CCSM3 scheme the ice thickness decreases with S-prec. A general result is that the modeled ice cover is rather sensitive to positive perturbations of the external heat supply when it is close to the transition such that just a small increase of, for example, F-wall can force the ice cover into the seasonal regime.

  • 2.
    Borenäs, Karin
    et al.
    SMHI, Core Services.
    Hietala, R.
    Laanearu, J.
    Lundberg, P.
    Some estimates of the Baltic deep-water transport through the Stolpe trench2007In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 59, no 2, p. 238-248Article in journal (Refereed)
    Abstract [en]

    The subsurface flow of high-saline water masses from the Bornholm Basin through the Stolpe Channel plays an important role for the renewal of the Baltic Central Basin deep waters. In order to determine whether rotating 11/2-layer hydraulic theory is an appropriate tool for describing this process, maximal-transport estimates based on climatological data from the Bornholm and Gdansk Basins have been established. These were found to deviate considerably from observational realities, and hence similar hydraulic considerations were also applied to more-or-less synoptic field data from a Finnish field campaign carried through in the mid-1980s. Also in this case significant differences were found between calculated transport capacity and observations. Since it furthermore was demonstrated that the characteristics of the observed cross-channel hydrographic structure could be explained using a frictional-balance model of the deep-water flow, it has been concluded that a hydraulic framework, although providing an upper bound of the transport, is of limited use when dealing with the Stolpe-Channel overflow. Although it cannot be excluded that the inflow is inviscid, but submaximal, it is more likely that the transport is governed by the combined effects of friction and wind forcing.

  • 3.
    Borenäs, Karin
    et al.
    SMHI, Core Services.
    Lake, Irene
    Lundberg, P A
    On the intermediate water masses of the Faroe-Bank Channel overflow2001In: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 31, no 7, p. 1904-1914Article in journal (Refereed)
    Abstract [en]

    A review of available hydrographic data from the Faroe-Bank Channel indicates that North Icelandic/Arctic Intermediate water masses are present in the passage to a larger extent than was previously believed. The presently compiled statistics, including results on the seasonality, are discussed in relation to previous investigations. Finally, a high quality subset of the hydrographic data is used for an analysis of the alongchannel mixing of the intermediate water masses.

  • 4.
    Borenäs, Karin
    et al.
    SMHI, Core Services.
    Lundberg, P
    The Faroe-Bank channel deep-water overflow2004In: Deep-sea research. Part II, Topical studies in oceanography, ISSN 0967-0645, E-ISSN 1879-0100, Vol. 51, no 4-5, p. 335-350Article in journal (Refereed)
    Abstract [en]

    In the late 1950s it was recognised that a considerable transport of water from the deeper reaches of the Norwegian Sea into the Atlantic takes place through the Faroe-Bank Channel, which thereby serves as an important source for the renewal of the North Atlantic Deep Water. Consequently, substantial efforts have, over the past decades, been dedicated towards quantifying the overflow as well as clarifying the underlying dynamics. In the present review, an attempt is made to summarise the main body of the observational results as well as some theoretical considerations regarding the dynamical mechanisms. The most prominent characteristic of the Faroe-Bank Channel overflow is that it is a persistent phenomenon with a yearly average deep-water (viz. T<5degreesC) transport of around 2 Sv. Using inviscid rotating hydraulics, the flow through the controlling section at the sill, furthermore, can be reasonably well predicted on the basis of upstream conditions in the Norwegian Sea. After passing the threshold the descending overflow plume is subject to intense mixing, a process very much in the focus of ongoing research. (C) 2004 Elsevier Ltd. All rights reserved.

  • 5. Enmar, Linda
    et al.
    Borenäs, Karin
    SMHI, Core Services.
    Lake, Irene
    SMHI, Core Services.
    Lundberg, Peter
    Comments on "Is the Faroe Bank Channel Overflow Hydraulically Controlled?''2009In: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 39, no 6, p. 1534-1538Article in journal (Other academic)
    Abstract [en]

    In a recent paper Girton et al., due to what appears to be a misunderstanding, stated that a critical-flow analysis of the deep-water transport through the Faroe Bank Channel had been undertaken by Lake et al. on the basis of rotating hydraulic theory for a channel of parabolic cross section. In fact, this quoted investigation dealt with a rectangular passage. In the present comment it is demonstrated how the use of parabolic bathymetry leads to significant improvements of the Froude number results.

  • 6. Eriksson, Leif E. B.
    et al.
    Borenäs, Karin
    SMHI, Core Services.
    Dierking, Wolfgang
    Berg, Anders
    Santoro, Maurizio
    Pemberton, Per
    SMHI, Research Department, Oceanography.
    Lindh, Henrik
    SMHI, Core Services.
    Karlson, Bengt
    SMHI, Research Department, Oceanography.
    Evaluation of new spaceborne SAR sensors for sea-ice monitoring in the Baltic Sea2010In: CANADIAN JOURNAL OF REMOTE SENSING, ISSN 1712-7971, Vol. 36, p. S56-S73Article in journal (Refereed)
    Abstract [en]

    In this study, synthetic aperture radar (SAR) data from the Advanced Land Observing Satellite (ALOS) and the Envisat, RADARSAT-2, and TerraSAR-X satellites were compared to evaluate their usefulness for sea-ice monitoring in the Baltic Sea. Radar signature characteristics at different frequencies, polarizations, and spatial resolutions are presented for three examples from 2009. C-band like-polarization data, which have been used for operational sea-ice mapping since the early 1990s, serve as a reference. Advantages and disadvantages were identified for the different SAR systems and imaging modes. One conclusion is that cross-polarized data improve the discrimination between sea ice and open water. Another observation is that it is easier to identify ice ridges in L-band data than in images from shorter wavelengths. The information content of X-and C-band images is largely equivalent, whereas L-band data provide complementary information. L-band SAR also seems to be less sensitive to wet snow cover on the ice.

  • 7.
    Lake, Irene
    et al.
    SMHI, Core Services.
    Borenäs, Karin
    SMHI, Core Services.
    Lundberg, P
    Potential-vorticity characteristics of the Faroe Bank Channel deep-water overflow2005In: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 35, no 6, p. 921-932Article in journal (Refereed)
    Abstract [en]

    Results from a 71-day deployment of three ADCP current meters on a section across the sill region of the Faroe Bank Channel are reported. The characteristic density structure of the channel, with warm, highly saline North Atlantic Ocean surface water overlying colder, less-saline deep water originating from the Nordic seas, lends itself well to a two-layer description of flow processes in this region. The dataset has been analyzed to describe the spatial and temporal characteristics of the deep-water potential vorticity. The most striking feature is a persistent cross-channel variation of this quantity, with higher values on the Faroe Bank side. In the 11/2-layer hydraulic calculations that were undertaken the potential vorticity was approximated as a linear distribution. The ADCP observations indicated that the deep-water flow was hydraulically controlled, and, using the direct observed transport, the analysis yielded diagnostic results for the upstream reservoir interface level that were in good agreement with observations. It was also concluded that the deviation of the potential vorticity from a constant value had no significant effects on the deep-water transport.

  • 8. Nikolopoulos, A
    et al.
    Borenäs, Karin
    SMHI, Core Services.
    Hietala, R
    Lundberg, P
    Hydraulic estimates of Denmark Strait overflow2003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no C3, article id 3095Article in journal (Refereed)
    Abstract [en]

    Upper bounds of the Denmark Strait deep-water overflow from the Nordic seas into the North Atlantic are estimated using rotating hydraulic theory. The calculations are made for the real bottom topography of the strait and are based on hydrographic sections surveyed during a dedicated field experiment in the area. Results are presented for zero as well as finite (but constant) potential vorticity, and it is shown that the differences in outcome between these two approaches are only minor. The calculated interface configurations are found to be in good agreement with those observed, and the theoretically obtained transports conform with earlier estimates.

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