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  • 1
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    Towards reliable Arctic sea ice prediction using multivariate data assimilation (2019)
    Elsevier
    In:  EPIC3Science Bulletin, Elsevier, 64, pp. 63-72
    Details
    Publication Date: 2019-01-29
    Description: Rapid declines in Arctic sea ice have captured attention and pose significant challenges to a variety of stakeholders. There is a rising demand for Arctic sea ice prediction at daily to seasonal time scales, which is partly a sea ice initial condition problem. Thus, a multivariate data assimilation that integrates sea ice observations to generate realistic and skillful model initialization is needed to improve predictive skill of Arctic sea ice. Sea ice data assimilation is a relatively new research area. In this review paper, we focus on two challenges for implementing multivariate data assimilation systems for sea ice forecast. First, to address the challenge of limited spatiotemporal coverage and large uncertainties of observations, we discuss sea ice parameters derived from satellite remote sensing that (1) have been utilized for improved model initialization, including concentration, thickness and drift, and (2) are currently under development with the potential for enhancing the predictability of Arctic sea ice, including melt ponds and sea ice leads. Second, to strive to generate the “best” estimate of sea ice initial conditions by combining model simulations/forecasts and observations, we review capabilities and limitations of different data assimilation techniques that have been developed and used to assimilate observed sea ice parameters in dynamical models.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Sea ice export through the Fram Strait derived from a combined model and satellite data set (2019)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3The Cryosphere, COPERNICUS GESELLSCHAFT MBH, 13(12), pp. 3209-3224, ISSN: 1994-0424
    Details
    Publication Date: 2020-05-15
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Arctic Ice Ocean Prediction System: evaluating sea-ice forecasts during Xuelong's first trans-Arctic Passage in summer 2017 (2019)
    INT GLACIOL SOC
    In:  EPIC3Journal of Glaciology, INT GLACIOL SOC, 65(253), pp. 813-821, ISSN: 0022-1430
    Details
    Publication Date: 2020-05-15
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Intensification and poleward shift of subtropical western boundary currents in a warming climate (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Oceans, Wiley, 121, pp. 4928-4945, ISSN: 0148-0227
    Details
    Publication Date: 2019-07-17
    Description: A significant increase in sea surface temperature (SST) is observed over the midlatitude western boundary currents (WBCs) during the past century. However, the mechanism for this phenomenon remains poorly understood due to limited observations. In the present paper, several coupled parameters (i.e., sea surface temperature (SST), ocean surface heat fluxes, ocean water velocity, ocean surface winds and sea level pressure (SLP)) are analyzed to identify the dynamic changes of the WBCs. Three types of independent data sets are used, including reanalysis products, satellite-blended observations. and climate model outputs from the fifth phase of the Climate Model Intercomparison Project (CMIP5). Based on these broad ranges of data, we find that the WBCs (except the Gulf Stream) are intensifying and shifting toward the poles as long-term effects of global warming. An intensification and poleward shift of near-surface ocean winds, attributed to positive annular mode-like trends, are proposed to be the forcing of such dynamic changes. In contrast to the other WBCs, the Gulf Stream is expected to be weaker under global warming, which is most likely related to a weakening of the Atlantic Meridional Overturning Circulation (AMOC). However, we also notice that the natural variations of WBCs might conceal the long-term effect of global warming in the available observational data sets, especially over the Northern Hemisphere. Therefore, long-term observations or proxy data are necessary to further evaluate the dynamics of the WBCs.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Ocean-atmosphere dynamics changes associated with prominent ocean surface turbulent heat fluxes trends during 1958–2013 (2016)
    In:  EPIC3Ocean Dynamics, 66(3), pp. 353-365, ISSN: 1616-7341
    Details
    Publication Date: 2019-07-17
    Description: In this study three prominent features of ocean surface turbulent heat fluxes (THF) trends during 1958-2013 are identifeed based on the Objectively Analyzed air-sea Fluxes (OAFlux). The associated ocean-atmosphere dynamics changes are investigated based on data of the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). First, the THF are enhanced over the mid-latitude expansions of the subtropical western boundary currents (WBCs). An intensified oceanic heat transport, forced by stronger near-surface zonal wind, is likely to be the cause of such THF tendency. Second, the THF are reduced over the tropical eastern Pacific Ocean, which is primarily caused by the decreasing near-surface wind speed and sea surface temperature (SST), associated with a local coupled ocean-atmosphere cooling mode. Finally, the THF are reduced over the northern tropical Atlantic Ocean, which is attributed to the decreasing air-sea humidity and temperature differences as a result of the convergence of near-surface air and the divergence of ocean currents (upwelling).
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Albedo of coastal landfast sea ice in Prydz Bay, Antarctica: Observations and parameterization (2016)
    In:  EPIC3Advances in Atmospheric Sciences, 33(5), pp. 535-543, ISSN: 0256-1530
    Details
    Publication Date: 2016-04-15
    Description: The snow/sea-ice albedo was measured over coastal landfast sea ice in Prydz Bay, East Antarctica (off Zhongshan Station) during the austral spring and summer of 2010 and 2011. The variation of the observed albedo was a combination of a gradual seasonal transition from spring to summer and abrupt changes resulting from synoptic events, including snowfall, blowing snow, and overcast skies. The measured albedo ranged from 0.94 over thick fresh snow to 0.36 over melting sea ice. It was found that snow thickness was the most important factor influencing the albedo variation, while synoptic events and overcast skies could increase the albedo by about 0.18 and 0.06, respectively. The in-situ measured albedo and related physical parameters (e.g., snow thickness, ice thickness, surface temperature, and air temperature) were then used to evaluate four different snow/ice albedo parameterizations used in a variety of climate models. The parameterized albedos showed substantial discrepancies compared to the observed albedo, particularly during the summer melt period, even though more complex parameterizations yielded more realistic variations than simple ones. A modified parameterization was developed, which further considered synoptic events, cloud cover, and the local landfast sea-ice surface characteristics. The resulting parameterized albedo showed very good agreement with the observed albedo.
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Assimilating summer sea-ice concentration into a coupled ice–ocean model using a LSEIK filter (2015)
    INT GLACIOL SOC
    In:  EPIC3Annals of Glaciology, INT GLACIOL SOC, 56(69), pp. 38-44, ISSN: 0260-3055
    Details
    Publication Date: 2019-07-17
    Description: The decrease in summer sea-ice extent in the Arctic Ocean opens shipping routes and creates potential for many marine operations. For these activities accurate predictions of sea-ice conditions are required to maintain marine safety. In an attempt at Arctic sea-ice prediction, the summer of 2010 is selected to implement an Arctic sea-ice data assimilation (DA) study. The DA system is based on a regional Arctic configuration of the Massachusetts Institute of Technology general circulation model (MITgcm) and a local singular evolutive interpolated Kalman (LSEIK) filter to assimilate Special Sensor Microwave Imager/Sounder (SSMIS) sea-ice concentration operational products from the US National Snow and Ice Data Center (NSIDC). Based on comparisons with both the assimilated NSIDC SSMIS concentration and concentration data from the Ocean and Sea Ice Satellite Application Facility, the forecasted sea-ice edge and concentration improve upon simulations without data assimilation. By the nature of the assimilation algorithm with multivariate covariance between ice concentration and thickness, sea-ice thickness fields are also updated, and the evaluation with in situ observation shows some improvement compared to the forecast without data assimilation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    Improving Arctic sea ice seasonal outlook by ensemble prediction using an ice-ocean model (2019)
    ELSEVIER SCIENCE INC
    In:  EPIC3Atmospheric Research, ELSEVIER SCIENCE INC, 227, pp. 14-23, ISSN: 0169-8095
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    Publication Date: 2020-05-15
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
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    Intensification and poleward shift of subtropical western boundary currents in a warming climate (2016)
    Wiley Online Library
    In:  EPIC3Journal of Geophysical Research: Oceans, Wiley Online Library, 121(7), pp. 4928-4945
    Details
    Publication Date: 2022-07-13
    Description: A significant increase in sea surface temperature (SST) is observed over the midlatitude western boundary currents (WBCs) during the past century. However, the mechanism for this phenomenon remains poorly understood due to limited observations. In the present paper, several coupled parameters (i.e., sea surface temperature (SST), ocean surface heat fluxes, ocean water velocity, ocean surface winds and sea level pressure (SLP)) are analyzed to identify the dynamic changes of the WBCs. Three types of independent data sets are used, including reanalysis products, satellite-blended observations. and climate model outputs from the fifth phase of the Climate Model Intercomparison Project (CMIP5). Based on these broad ranges of data, we find that the WBCs (except the Gulf Stream) are intensifying and shifting toward the poles as long-term effects of global warming. An intensification and poleward shift of near-surface ocean winds, attributed to positive annular mode-like trends, are proposed to be the forcing of such dynamic changes. In contrast to the other WBCs, the Gulf Stream is expected to be weaker under global warming, which is most likely related to a weakening of the Atlantic Meridional Overturning Circulation (AMOC). However, we also notice that the natural variations of WBCs might conceal the long-term effect of global warming in the available observational data sets, especially over the Northern Hemisphere. Therefore, long-term observations or proxy data are necessary to further evaluate the dynamics of the WBCs.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 10
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    Intensification and poleward shift of subtropical western boundary currents under global warming (2015)
    EGU General Assembly 2015
    In:  EPIC3EGU General Assembly 2015, Vienna, Austria, 2015-04-12-2015-04-17EGU General Assembly 2015
    Details
    Publication Date: 2022-09-29
    Description: Dynamic changes of subtropical western boundary currents (WBCs) are investigated based on three types of independent data sets. These include reconstructed and reanalysis products, satellite/blended observations and climate models output from the fifth phase of the Climate Model Intercomparison Project (CMIP5). Consistent increasing of sea surface temperature (SST) and ocean surface heat loss are found over the mid-latitude expansions of WBCs. Furthermore, the upper 100 m ocean water velocity are increasing in the same direction as the background WBCs, demonstrating that WBCs are strengthening. In addition, the positions of WBCs induced sharp SST fronts and intensive ocean heat loss are migrating towards the poles, suggesting that the routes of WBCs are shifting poleward. According to the ensemble projections from the CMIP5 models, the WBCs (except the Gulf Stream) will continue strengthening and shifting poleward if carbon dioxide levels keep rising in this century. The significant dynamic changes of WBCs are affected by an intensified and poleward shift of near-surface ocean zonal winds, which are attributed to positive annular modes-like trends, particularly over the Southern Hemisphere.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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