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• 1. [Article] Frontal Scale Air–Sea Interaction in High-Resolution Coupled Climate Models

  The emerging picture of frontal scale air–sea interaction derived from high-resolution satellite observations of surface winds and sea surface temperature (SST) provides a unique opportunity to test the ...

  Citation × Citation Citation Abstract Copy Title: Frontal Scale Air–Sea Interaction in High-Resolution Coupled Climate Models Author: Chelton, Dudley B., McClean, Julie L., Loeb, Norman G., Dennis, John M., Bryan, Frank O., Tomas, Robert The emerging picture of frontal scale air–sea interaction derived from high-resolution satellite observations of surface winds and sea surface temperature (SST) provides a unique opportunity to test the fidelity of high-resolution coupled climate simulations. Initial analysis of the output of a suite of Community Climate System Model (CCSM) experiments indicates that characteristics of frontal scale ocean–atmosphere interaction, such as the positive correlation between SST and surface wind stress, are realistically captured only when the ocean component is eddy resolving. The strength of the coupling between SST and surface stress is weaker than observed, however, as has been found previously for numerical weather prediction models and other coupled climate models. The results are similar when the atmospheric component model grid resolution is doubled from 0.5° to 0.25°, an indication that shortcomings in the representation of subgrid scale atmospheric planetary boundary layer processes, rather than resolved scale processes, are responsible for the weakness of the coupling. In the coupled model solutions the response to mesoscale SST features is strongest in the atmospheric boundary layer, but there is a deeper reaching response of the atmospheric circulation apparent in free tropospheric clouds. This simulated response is shown to be consistent with satellite estimates of the relationship between mesoscale SST and all-sky albedo. Title: Frontal Scale Air–Sea Interaction in High-Resolution Coupled Climate Models Author: Chelton, Dudley B., McClean, Julie L., Loeb, Norman G., Dennis, John M., Bryan, Frank O., Tomas, Robert The emerging picture of frontal scale air–sea interaction derived from high-resolution satellite observations of surface winds and sea surface temperature (SST) provides a unique opportunity to test the fidelity of high-resolution coupled climate simulations. Initial analysis of the output of a suite of Community Climate System Model (CCSM) experiments indicates that characteristics of frontal scale ocean–atmosphere interaction, such as the positive correlation between SST and surface wind stress, are realistically captured only when the ocean component is eddy resolving. The strength of the coupling between SST and surface stress is weaker than observed, however, as has been found previously for numerical weather prediction models and other coupled climate models. The results are similar when the atmospheric component model grid resolution is doubled from 0.5° to 0.25°, an indication that shortcomings in the representation of subgrid scale atmospheric planetary boundary layer processes, rather than resolved scale processes, are responsible for the weakness of the coupling. In the coupled model solutions the response to mesoscale SST features is strongest in the atmospheric boundary layer, but there is a deeper reaching response of the atmospheric circulation apparent in free tropospheric clouds. This simulated response is shown to be consistent with satellite estimates of the relationship between mesoscale SST and all-sky albedo. Close

• 2. [Article] Trajectory Analysis of Black Carbon in the Arctic Region

  Black carbon (BC) is a troubling particulate. Commonly known as soot, BC forms through the incomplete combustion of fossil fuels, biofuels, and biomass. It has a very low albedo compared to natural particulates ...

  Citation × Citation Citation Abstract Copy Title: Trajectory Analysis of Black Carbon in the Arctic Region Author: Gottschalk, Kimberly Year: 2016 Black carbon (BC) is a troubling particulate. Commonly known as soot, BC forms through the incomplete combustion of fossil fuels, biofuels, and biomass. It has a very low albedo compared to natural particulates making it a very efficient absorber of solar radiation. As BC is deposited on snow and ice, albedo is decreased - enhancing solar heating and increasing meltwater production. With rising air temperatures, melting rates of polar ice are increasing and are being enhanced by BC, leading to accelerated global sea level rise. This study aimed to document sources and deposition areas of BC in the Arctic. Utilizing HySplit, an air trajectory model, patterns of BC trajectories are assessed. Spatial patterns of deposition are estimated from known sources and source regions predicted from known deposition locations through the use of backward trajectory. Atmospheric circulation transports BC from temperate regions into the Arctic. The strength and location of the polar front in relation to the North Atlantic Oscillation is a dominant controlling factor. Preliminary results show reoccurring potential sources located in the Northeastern United States, Nova Scotia, Northern United Kingdom, and the Scandinavian Peninsula with large deposition events occurring within the first six months of the year. Title: Trajectory Analysis of Black Carbon in the Arctic Region Author: Gottschalk, Kimberly Year: 2016 Black carbon (BC) is a troubling particulate. Commonly known as soot, BC forms through the incomplete combustion of fossil fuels, biofuels, and biomass. It has a very low albedo compared to natural particulates making it a very efficient absorber of solar radiation. As BC is deposited on snow and ice, albedo is decreased - enhancing solar heating and increasing meltwater production. With rising air temperatures, melting rates of polar ice are increasing and are being enhanced by BC, leading to accelerated global sea level rise. This study aimed to document sources and deposition areas of BC in the Arctic. Utilizing HySplit, an air trajectory model, patterns of BC trajectories are assessed. Spatial patterns of deposition are estimated from known sources and source regions predicted from known deposition locations through the use of backward trajectory. Atmospheric circulation transports BC from temperate regions into the Arctic. The strength and location of the polar front in relation to the North Atlantic Oscillation is a dominant controlling factor. Preliminary results show reoccurring potential sources located in the Northeastern United States, Nova Scotia, Northern United Kingdom, and the Scandinavian Peninsula with large deposition events occurring within the first six months of the year. Close

• 3. [Article] Response of marine stratus to successive polluting events by ships

  Ship tracks have proven to be an ideal laboratory for studying the response of marine stratocumulus to an increase in aerosol pollution. Here the response of already polluted marine stratocumulus to further ...

  Citation × Citation Citation Abstract Copy Title: Response of marine stratus to successive polluting events by ships Author: Sechrist, B. Ship tracks have proven to be an ideal laboratory for studying the response of marine stratocumulus to an increase in aerosol pollution. Here the response of already polluted marine stratocumulus to further pollution was examined by studying the clouds where two ship tracks cross. 78 crossings of ship tracks were collected and analyzed using Terra and Aqua MODIS multispectral satellite daytime imagery for summertime passes off the west coast of the U.S. Partly cloudy pixels, though collected and compared to overcast pixels, were excluded from the analysis of the crossings in order to reduce biases in the retrieved cloud properties caused by subpixel spatial variation among the clouds. When clouds were polluted by the plume of a ship, the visible optical depth and the column droplet number concentration increased significantly. The cloud droplet radius decreased significantly, while the cloud liquid water path decreased slightly. The cloud temperature was unchanged. Of any two ship tracks that crossed, one of the tracks exhibited a much larger change in droplet radius compared to the control clouds than did the other track compared to the control clouds. This dominant ship track typically displayed properties closer to those of the clouds at the crossing than did the subordinate ship track. Local gradients in the retrieved cloud properties were determined for both the dominant and subordinate ship tracks. The values of the gradients at the crossing were used as proxies for what the cloud properties would have been if the clouds had been polluted by only one ship. The differences between the retrieved properties of the clouds in the crossing pixels and the values established by the gradients represented the response of the clouds in one ship track to pollution by a second ship. The responses to pollution by the dominant ship were compared for the uncontaminated control clouds and the clouds that had already been polluted by the subordinate ship. The same analysis was repeated with the subordinate ship polluting both the uncontaminated control clouds and the clouds that had already been polluted by the dominant ship. These comparisons revealed that the response to additional aerosol loading was diminished for clouds that had already been polluted. The decreased response at higher aerosol concentrations was observed for the optical depth, the droplet radius, and the column droplet number concentration. Cloud susceptibility was also examined by comparing the response to pollution of optically thin clouds with that of optically thick clouds. The visible reflectivity of the optically thin clouds was observed to be highly susceptible to an increase in column droplet number concentration, while the reflectivity of the optically thick clouds proved to be insensitive. Title: Response of marine stratus to successive polluting events by ships Author: Sechrist, B. Ship tracks have proven to be an ideal laboratory for studying the response of marine stratocumulus to an increase in aerosol pollution. Here the response of already polluted marine stratocumulus to further pollution was examined by studying the clouds where two ship tracks cross. 78 crossings of ship tracks were collected and analyzed using Terra and Aqua MODIS multispectral satellite daytime imagery for summertime passes off the west coast of the U.S. Partly cloudy pixels, though collected and compared to overcast pixels, were excluded from the analysis of the crossings in order to reduce biases in the retrieved cloud properties caused by subpixel spatial variation among the clouds. When clouds were polluted by the plume of a ship, the visible optical depth and the column droplet number concentration increased significantly. The cloud droplet radius decreased significantly, while the cloud liquid water path decreased slightly. The cloud temperature was unchanged. Of any two ship tracks that crossed, one of the tracks exhibited a much larger change in droplet radius compared to the control clouds than did the other track compared to the control clouds. This dominant ship track typically displayed properties closer to those of the clouds at the crossing than did the subordinate ship track. Local gradients in the retrieved cloud properties were determined for both the dominant and subordinate ship tracks. The values of the gradients at the crossing were used as proxies for what the cloud properties would have been if the clouds had been polluted by only one ship. The differences between the retrieved properties of the clouds in the crossing pixels and the values established by the gradients represented the response of the clouds in one ship track to pollution by a second ship. The responses to pollution by the dominant ship were compared for the uncontaminated control clouds and the clouds that had already been polluted by the subordinate ship. The same analysis was repeated with the subordinate ship polluting both the uncontaminated control clouds and the clouds that had already been polluted by the dominant ship. These comparisons revealed that the response to additional aerosol loading was diminished for clouds that had already been polluted. The decreased response at higher aerosol concentrations was observed for the optical depth, the droplet radius, and the column droplet number concentration. Cloud susceptibility was also examined by comparing the response to pollution of optically thin clouds with that of optically thick clouds. The visible reflectivity of the optically thin clouds was observed to be highly susceptible to an increase in column droplet number concentration, while the reflectivity of the optically thick clouds proved to be insensitive. Close

• 4. [Article] Modeling Arctic melt ponds using a resolved ice model with GCM forcing

  The albedo of Arctic sea ice depends greatly on the formation of melt ponds. These ponds form in depressions on the ice as surface snow melts during the summer months, and their location is determined ...

  Citation × Citation Citation Abstract Copy Title: Modeling Arctic melt ponds using a resolved ice model with GCM forcing Author: Collins, Lee E. The albedo of Arctic sea ice depends greatly on the formation of melt ponds. These ponds form in depressions on the ice as surface snow melts during the summer months, and their location is determined mainly by the initial snow topography. Using a high resolution sea ice model forced with data taken from the Atmospheric Radiation Measurement (ARM) site in Barrow, AK, we investigate how specific factors, both internal model parameters and initial conditions, affect the evolution of melt ponds on Arctic sea ice. We also use forcing data taken from output of the Community Earth Systems Model (CESM) to investigate the differences in melt pond parametrization between our model and CESM. The resolved model uses a unique and innovative approach in pond modeling, the trigger depth method, to initiate pond drainage. Results from sensitivity analysis on the trigger depth show the validity of this new approach, suggesting it could be useful in other ice models. The initial snowpack has a very large role in pond formation and extent. We use surface topography gathered from LiDAR scans from the ARM site to provide a realistic snowpack surface. For our sensitivity analysis of the total initial amount of snow in the model, we alter only the minimum thickness of the snow on top of the ice, retaining a consistent surface topography for each simulation. The LiDAR topography from the ARM site provides a more realistic approach to the pond model, as opposed to a randomly generated method of creating snow topography. Large initial snowpack inhibits the formation of deep channels in the ice, reducing pond fraction at the end of the melt season. Finally, we force the resolved model simulations with data from CESM and compare the pond behavior to that of CESM. CESM does an unrealistic job of representing melt ponds, partially due to the way melt ponds are parametrized in the model, using a thickness-class method for creating and categorizing melt ponds. CESM pond formation occurs over a much broader time span compared to observations and our resolved model. Results from this work will be used to investigate and possibly improve the melt pond parametrization in CESM. Title: Modeling Arctic melt ponds using a resolved ice model with GCM forcing Author: Collins, Lee E. The albedo of Arctic sea ice depends greatly on the formation of melt ponds. These ponds form in depressions on the ice as surface snow melts during the summer months, and their location is determined mainly by the initial snow topography. Using a high resolution sea ice model forced with data taken from the Atmospheric Radiation Measurement (ARM) site in Barrow, AK, we investigate how specific factors, both internal model parameters and initial conditions, affect the evolution of melt ponds on Arctic sea ice. We also use forcing data taken from output of the Community Earth Systems Model (CESM) to investigate the differences in melt pond parametrization between our model and CESM. The resolved model uses a unique and innovative approach in pond modeling, the trigger depth method, to initiate pond drainage. Results from sensitivity analysis on the trigger depth show the validity of this new approach, suggesting it could be useful in other ice models. The initial snowpack has a very large role in pond formation and extent. We use surface topography gathered from LiDAR scans from the ARM site to provide a realistic snowpack surface. For our sensitivity analysis of the total initial amount of snow in the model, we alter only the minimum thickness of the snow on top of the ice, retaining a consistent surface topography for each simulation. The LiDAR topography from the ARM site provides a more realistic approach to the pond model, as opposed to a randomly generated method of creating snow topography. Large initial snowpack inhibits the formation of deep channels in the ice, reducing pond fraction at the end of the melt season. Finally, we force the resolved model simulations with data from CESM and compare the pond behavior to that of CESM. CESM does an unrealistic job of representing melt ponds, partially due to the way melt ponds are parametrized in the model, using a thickness-class method for creating and categorizing melt ponds. CESM pond formation occurs over a much broader time span compared to observations and our resolved model. Results from this work will be used to investigate and possibly improve the melt pond parametrization in CESM. Close