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  • 1
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    Role of internal variability in recent decadal to multidecadal tropical Pacific climate changes (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 44 (9). pp. 4246-4255.
    Details
    Publication Date: 2020-02-06
    Description: While the Earth's surface has considerably warmed over the past two decades, the tropical Pacific has featured a cooling of sea surface temperatures in its eastern and central parts, which went along with an unprecedented strengthening of the equatorial trade winds, the surface component of the Pacific Walker Circulation (PWC). Previous studies show that this decadal trend in the trade winds is generally beyond the range of decadal trends simulated by climate models when forced by historical radiative forcing. There is still a debate on the origin of and the potential role that internal variability may have played in the recent decadal surface wind trend. Using a number of long control (unforced) integrations of global climate models and several observational data sets, we address the question as to whether the recent decadal to multidecadal trends are robustly classified as an unusual event or the persistent response to external forcing. The observed trends in the tropical Pacific surface climate are still within the range of the long-term internal variability spanned by the models but represent an extreme realization of this variability. Thus, the recent observed decadal trends in the tropical Pacific, though highly unusual, could be of natural origin. We note that the long-term trends in the selected PWC indices exhibit a large observational uncertainty, even hindering definitive statements about the sign of the trends.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/2016GL072355
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Coupled North Atlantic Sub-decadal Variability in CMIP5 Models (2019)
    Wiley | AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 124 (4). pp. 2404-2417.
    Details
    Publication Date: 2022-01-31
    Description: The interaction between the atmosphere, specifically the North Atlantic Oscillation (NAO), and the North Atlantic ocean circulation on sub‐decadal timescale is analyzed in a subset of models participating in the Coupled Model Intercomparison Project phase 5 (CMIP5). From preindustrial control runs of at least 500 years length, we derive anomaly patterns in the atmospheric and ocean circulation and of air‐sea heat exchange. All models simulate a distinct dipolar oceanic overturning anomaly at the sub‐decadal timescale, with centers at 30° N and 55° N. The dipolar overturning anomaly goes along with marked anomalies in the North Atlantic sea surface temperature and gyre circulation. Lag‐regression analyses demonstrate, with relatively small ensemble spread, how the atmosphere and the ocean circulation interact. The dipolar anomalies in the overturning are forced by NAO‐related wind stress curl anomalies. Anomalous surface heat fluxes in concert with anomalous vertical motions drive a meridional dipolar heat content anomaly in the upper ocean, and it is this dipolar heat content anomaly which carries the coupled system from one phase of the sub‐decadal cycle to the other by reversing the tendencies in the overturning circulation. The coupled sub‐decadal variability derived from the CMIP5 models is characterized by three elements: a wind‐driven part steering the dipolar overturning anomaly, surface heat flux anomalies that support a heat build‐up in the subpolar gyre region, and the heat storage memory which is instrumental in the phase reversal of the NAO.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2018JC014539
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Large-scale drift of Arctic Sea ice retrieved from passive microwave satellite data (2000)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 105 (C4). pp. 8775-8788.
    Details
    Publication Date: 2018-04-17
    Description: A method of determining the large‐scale sea ice drift using 85.5 GHz Special Sensor Microwave Imager data are presented. A cross‐correlation method is applied to sequential images of gridded data covering the entire Arctic. Individual correlation results are validated with ice velocities derived from buoy data. The satellite‐derived mean drift values and the variabilities of the ice drift correspond closely with the buoy data. Similarly, time series of buoy data and associated satellite data are in good agreement even over large time periods. An example of a satellite‐retrieved 3 day mean drift field demonstrates the potential of the method for providing large‐scale ice circulation patterns. Mean drift fields of the winter periods 1987–1988 and 1992–1993 indicate a considerable interannual variability of the sea ice drift pattern in the Arctic Ocean. The Arctic region is divided into seven larger areas, and the area flux between these regions has been derived. The Kara Sea and the Laptev Sea show the largest area ice export with 0.02 and 0.015 km2 s−1, respectively. The central Arctic export through Fram Strait amounts to 0.12 Sv during the winter of 1992–1993 with a maximum of 0.15 Sv in January.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/1999JC900270
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Sea ice circulation in the Laptev Sea and ice export to the Arctic Ocean: Sea ice circulation in the Laptev Sea and ice export to the Arctic Ocean: Results from satellite remote sensing and numerical modeling (2000)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 105 (C7). pp. 17-143.
    Details
    Publication Date: 2018-04-18
    Description: Sea ice circulation in the Laptev Sea and ice exchange with the Arctic Ocean have been studied based on remote sensing data and numerical modeling. Ice drift patterns for short‐ and long‐term periods were retrieved from successive Okean radar images and Special Sensor Microwave/Imager data for the winters 1987/1988 and 1994/1995. Seasonal and interannual variabilities of ice drift in the Laptev Sea and ice exchange with the Arctic Ocean during the period from 1979 to 1995 were studied with a large‐scale dynamic‐thermodynamic sea ice model. During an “average year,” sea ice was exported from the Laptev Sea through its northern and eastern boundaries, with maximum and minimum export occurring in February and August, respectively. The winter ice outflow from the Laptev Sea varied between 251,000 km2 (1984/1985) and 732,000 km2 (1988/1989) with the mean value of 483,000 km2. Sea ice was exported into the East Siberian Sea mostly in summers with the mean value of 69,000 km2. Out of the 17 investigated summers, 12 were characterized by sea ice import from the Arctic Ocean into the Laptev Sea through its northern boundary. Magnitude and direction of ice export from the Laptev Sea corresponded with the large‐scale Arctic Ocean drift patterns during periods of prevailing cyclonic or anticyclonic circulation. Based on a semiempirical method that has been validated with the large‐scale model and satellite data, ice exchange between the Laptev Sea and the Arctic Ocean during the period from 1936 to 1995 has been estimated as 309,000km2 with strong interannual variability and no significant trend apparent.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2000JC900029
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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