Bare Ice Albedo Research Articles

Modelled and satellite‐derived surface albedo of lake ice – Part I: evaluation of the albedo parameterization scheme of the Canadian Lake Ice Model

AbstractAccurate simulations of freshwater lake ice are integral for the study of climatic variability in northern environments. Surface albedo, a component often parameterized in lake ice models, has been shown to affect the timing of ice break‐up during the melt season. In situ snow and ice albedo measurements were taken over a partially snow‐covered freshwater lake near Churchill, Manitoba for the evaluation of the albedo parameterization of the Canadian Lake Ice Model (CLIMo) and the Moderate Resolution Imaging Spectrometer (MODIS) albedo products (MOD10A1/MYD10A1 and MCD43A3). The albedo simulations using CLIMo were performed with and without snow integrated into the model and evaluated against in situ albedo measurements recorded over clear ice, snow ice and snow‐covered ice. The simulated snow albedo from CLIMo for the entire ice growth season evaluated against snow albedo observations had a root mean square error of 0.07, a mean absolute error of 0.06, and a mean bias error (MBE) of −0.01. With snow removed from CLIMo, the albedo parameterization overestimated albedo values measured in the field over snow‐free clear ice and snow ice with MBE values of 0.13 and 0.10, respectively. These findings suggest that CLIMo's bare ice albedo parameterization needs to be revised to account for albedo differences between ice types.The evaluation of the MODIS albedo products with in situ snow and ice albedo observations and the comparison of these satellite products with CLIMo's albedo parameterization during the melt period, when in situ radiation measurement stations needed to be removed from the lake‐ice surface, are addressed in paper Part II (this issue). Copyright © 2014 John Wiley & Sons, Ltd.

Simulating the mass balance and salinity of Arctic and Antarctic sea ice. 2. Importance of sea ice salinity variations

Sea ice has a non-zero salinity that varies in space and time. This affects the sea ice thermal properties as well as the ice–ocean salt and freshwater exchanges, which may influence the sea ice mass balance and the polar oceans’ characteristics. However, current sea ice models neglect or misrepresent the ice salinity. In this paper, we address the question of the importance of large-scale sea ice salinity variations for the sea ice mass balance and the upper ocean. To examine this question, we formulate salinity variations in the framework of the sea ice thickness distribution theory, using a simple parameterization for brine entrapment and drainage. The latter is tested one-dimensionally and then included in a three-dimensional large-scale ice–ocean model, OPA9-LIM3, which is run over 1970–2006, forced by a combination of atmospheric reanalyses and climatologies. Due to differences in the physical forcings, the model simulates Arctic and Antarctic sea ice salinity fields that profoundly differ, with a seasonal cycle that is found in reasonable agreement with available ice core data. Then, the role of salinity variations is analyzed by comparing the results of the simulation including the interactive salinity with several sensitivity runs using simpler representations of ice salinity. The simulated large-scale sea ice mass balance and upper ocean characteristics are found to be quite sensitive to the representation of ice salinity. In the Arctic, salinity variations induce changes in ice thickness up to one meter in some regions, due to modifications in the sea ice thermal properties. Around Antarctica, including salinity variations increases the simulated winter sea ice volume by up to 28% because of changes in ice–ocean interactions that stabilize the ocean. The model sensitivity to the sea ice salinity is of the same order of magnitude as a 10% change in bare ice albedo. Given the importance of salinity on the simulated sea ice characteristics, sea ice salinity variations should be included in assessments of the response of the high-latitude oceans to ongoing and future climate change.

Reply to comment by E. T. DeWeaver et al. on “On the reliability of simulated Arctic sea ice in global climate models”

Reply to comment by E. T. DeWeaver et al. on “On the reliability of simulated Arctic sea ice in global climate models”

The sensitivity of a thermodynamic sea ice model to changes in surface albedo parameterization

The sensitivity of a thermodynamic sea ice model to changes in surface energy fluxes in the Arctic is investigated. The main emphasis of the paper is on the testing of the model sensitivity to changes in surface albedo parameterization. Climatologies of turbulent and long‐wave fluxes in the Arctic are scarce, and those that exist are shown to generate significant differences in the predicted ice thickness. There is considerable disagreement in the literature on albedo values, and in particular, proposed albedos of bare, puddled ice range from 0.4 to 0.66. The differences among published model simulations are shown to be potentially explicable in terms of this range in bare ice albedo. A new ice albedo parameterization is proposed, and its sensitivity is tested. It is shown that the increase in surface albedo with cloud cover can cause a doubling of the ice thickness, and the need to include melting snow as an albedo class distinct from dry snow is demonstrated. The value of bare‐ice albedo is shown to be important in determining whether the ice is in a multiyear or a seasonal ice zone, and the need for more observational data on the extent and role of melt puddles is emphasized.