Search Results
You are looking at 1 - 3 of 3 items for :
- Author or Editor: Jinlun Zhang x
- Journal of Physical Oceanography x
- Refine by Access: All Content x
Abstract
The theory of sea ice thickness distribution developed by Thorndike et al. has been extended to include sea ice enthalpy distribution. The extended theory conserves both ice mass and thermal energy, in the form of the heat stored in the ice, by jointly solving a thickness-distribution equation and an enthalpy-distribution equation. Both equations have been implemented in a one-dimensional dynamic thermodynamic sea-ice model with 12 ice thickness categories following the numerical procedure of Hibler. The implementation of the enthalpy-distribution equation allows the sea-ice model to account for any changes in the ice thermal energy induced by sea ice processes. As a result, the model is able to conserve not only the ice mass but also its thermal energy in the presence of ice advection, growth, melting, and ridging. Conserving ice thermal energy in a thickness-distribution sea ice model improves the prediction of ice growth, summer ice melt in particular, and therefore ice thickness. Inability to conserve the thermal energy by not implementing the enthalpy-distribution equation, compounded with an effect of the surface albedo feedback, causes the model to underestimate ice thickness by up to 11% under various conditions of thermal and mechanical forcing. This indicates the importance of conserving energy in numerical investigations of climate.
Abstract
The theory of sea ice thickness distribution developed by Thorndike et al. has been extended to include sea ice enthalpy distribution. The extended theory conserves both ice mass and thermal energy, in the form of the heat stored in the ice, by jointly solving a thickness-distribution equation and an enthalpy-distribution equation. Both equations have been implemented in a one-dimensional dynamic thermodynamic sea-ice model with 12 ice thickness categories following the numerical procedure of Hibler. The implementation of the enthalpy-distribution equation allows the sea-ice model to account for any changes in the ice thermal energy induced by sea ice processes. As a result, the model is able to conserve not only the ice mass but also its thermal energy in the presence of ice advection, growth, melting, and ridging. Conserving ice thermal energy in a thickness-distribution sea ice model improves the prediction of ice growth, summer ice melt in particular, and therefore ice thickness. Inability to conserve the thermal energy by not implementing the enthalpy-distribution equation, compounded with an effect of the surface albedo feedback, causes the model to underestimate ice thickness by up to 11% under various conditions of thermal and mechanical forcing. This indicates the importance of conserving energy in numerical investigations of climate.
Abstract
A coupled sea ice–ocean model is developed to quantify the sea ice response to changes in atmospheric and oceanic forcing in the Bering Sea over the period 1970–2008. The model captures much of the observed spatiotemporal variability of sea ice and sea surface temperature (SST) and the basic features of the upper-ocean circulation in the Bering Sea. Model results suggest that tides affect the spatial redistribution of ice mass by up to 0.1 m or 15% in the central-eastern Bering Sea by modifying ice motion and deformation and ocean flows. The considerable interannual variability in the pattern and strength of winter northeasterly winds leads to southwestward ice mass advection during January–May, ranging from 0.9 × 1012 m3 in 1996 to 1.8 × 1012 m3 in 1976 and averaging 1.4 × 1012 m3, which is almost twice the January–May mean total ice volume in the Bering Sea. The large-scale southward ice mass advection is constrained by warm surface waters in the south that melt 1.5 × 1012 m3 of ice in mainly the ice-edge areas during January–May, with substantial interannual variability ranging from 0.94 × 1012 m3 in 1996 to 2.0 × 1012 m3 in 1976. Ice mass advection processes also enhance thermodynamic ice growth in the northern Bering Sea by increasing areas of open water and thin ice. Ice growth during January–May is 0.90 × 1012 m3 in 1996 and 2.1 × 1012 m3 in 1976, averaging 1.3 × 1012 m3 over 1970–2008. Thus, the substantial interannual variability of the Bering Sea ice cover is dominated by changes in the wind-driven ice mass advection and the ocean thermal front at the ice edge. The observed ecological regime shifts in the Bering Sea occurred with significant changes in sea ice, surface air temperature, and SST, which in turn are correlated with the Pacific decadal oscillation over 1970–2008 but not with other climate indices: Arctic Oscillation, North Pacific index, and El Niño–Southern Oscillation. This indicates that the PDO index may most effectively explain the regime shifts in the Bering Sea.
Abstract
A coupled sea ice–ocean model is developed to quantify the sea ice response to changes in atmospheric and oceanic forcing in the Bering Sea over the period 1970–2008. The model captures much of the observed spatiotemporal variability of sea ice and sea surface temperature (SST) and the basic features of the upper-ocean circulation in the Bering Sea. Model results suggest that tides affect the spatial redistribution of ice mass by up to 0.1 m or 15% in the central-eastern Bering Sea by modifying ice motion and deformation and ocean flows. The considerable interannual variability in the pattern and strength of winter northeasterly winds leads to southwestward ice mass advection during January–May, ranging from 0.9 × 1012 m3 in 1996 to 1.8 × 1012 m3 in 1976 and averaging 1.4 × 1012 m3, which is almost twice the January–May mean total ice volume in the Bering Sea. The large-scale southward ice mass advection is constrained by warm surface waters in the south that melt 1.5 × 1012 m3 of ice in mainly the ice-edge areas during January–May, with substantial interannual variability ranging from 0.94 × 1012 m3 in 1996 to 2.0 × 1012 m3 in 1976. Ice mass advection processes also enhance thermodynamic ice growth in the northern Bering Sea by increasing areas of open water and thin ice. Ice growth during January–May is 0.90 × 1012 m3 in 1996 and 2.1 × 1012 m3 in 1976, averaging 1.3 × 1012 m3 over 1970–2008. Thus, the substantial interannual variability of the Bering Sea ice cover is dominated by changes in the wind-driven ice mass advection and the ocean thermal front at the ice edge. The observed ecological regime shifts in the Bering Sea occurred with significant changes in sea ice, surface air temperature, and SST, which in turn are correlated with the Pacific decadal oscillation over 1970–2008 but not with other climate indices: Arctic Oscillation, North Pacific index, and El Niño–Southern Oscillation. This indicates that the PDO index may most effectively explain the regime shifts in the Bering Sea.
Abstract
To understand the factors causing the interannual variations in the summer retreat of the Beaufort Sea ice edge, Seasonal Ice Zone Reconnaissance Surveys (SIZRS) aboard U.S. Coast Guard Arctic Domain Awareness flights were made monthly from June to October in 2012, 2013, and 2014. The seasonal ice zone (SIZ) is where sea ice melts and reforms annually and encompasses the nominally narrower marginal ice zone (MIZ) where a mix of open-ocean and ice pack processes prevail. Thus, SIZRS provides a regional context for the smaller-scale MIZ processes. Observations with aircraft expendable conductivity–temperature–depth probes reveal a salinity pattern associated with large-scale gyre circulation and the seasonal formation of a shallow (~20 m) fresh layer moving with the ice edge position. Repeat occupations of the SIZRS lines from 72° to 76°N on 140° and 150°W allow a comparison of observed hydrography to atmospheric indices. Using this relationship, the basinwide salinity signals are separated from the fresh layer associated with the ice edge. While this layer extends northward under the ice edge as the melt season progresses, low salinities and warm temperatures appear south of the edge. Within this fresh layer, average salinity is correlated with distance from the ice edge. The salinity observations suggest that the upper-ocean freshening over the summer is dominated by local sea ice melt and vertical mixing. A Price–Weller–Pinkel model analysis reveals that observed changes in heat content and density structure are also consistent with a 1D mixing process.
Abstract
To understand the factors causing the interannual variations in the summer retreat of the Beaufort Sea ice edge, Seasonal Ice Zone Reconnaissance Surveys (SIZRS) aboard U.S. Coast Guard Arctic Domain Awareness flights were made monthly from June to October in 2012, 2013, and 2014. The seasonal ice zone (SIZ) is where sea ice melts and reforms annually and encompasses the nominally narrower marginal ice zone (MIZ) where a mix of open-ocean and ice pack processes prevail. Thus, SIZRS provides a regional context for the smaller-scale MIZ processes. Observations with aircraft expendable conductivity–temperature–depth probes reveal a salinity pattern associated with large-scale gyre circulation and the seasonal formation of a shallow (~20 m) fresh layer moving with the ice edge position. Repeat occupations of the SIZRS lines from 72° to 76°N on 140° and 150°W allow a comparison of observed hydrography to atmospheric indices. Using this relationship, the basinwide salinity signals are separated from the fresh layer associated with the ice edge. While this layer extends northward under the ice edge as the melt season progresses, low salinities and warm temperatures appear south of the edge. Within this fresh layer, average salinity is correlated with distance from the ice edge. The salinity observations suggest that the upper-ocean freshening over the summer is dominated by local sea ice melt and vertical mixing. A Price–Weller–Pinkel model analysis reveals that observed changes in heat content and density structure are also consistent with a 1D mixing process.
