Investigating Future Arctic Sea Ice Loss and Near‐Surface Wind Speed Changes Related to Surface Roughness Using the Community Earth System Model
The Arctic is undergoing a pronounced and rapid transformation in response to changing greenhouse gasses, including a reduction in sea ice extent and thickness. There are also projected increases in near-surface Arctic wind. Decreasing sea ice concentration is making the Arctic more accessible, and the combination of more open water with stronger winds can lead to larger wave heights, which drive coastal erosion and can be a hazard to ships. Therefore, it is particularly important to fully understand the relationships between sea ice loss and near-surface winds due to the large human and physical system impacts. Two possible drivers of increasing Arctic near-surface winds are (1) reduced atmospheric stability due to enhanced surface warming as sea ice melts could lead to enhanced turbulent transport from the free troposphere downward, and (2) reduction in surface roughness due to the transition from sea ice cover to open ocean could lead to an acceleration of near-surface winds.
This study addresses how wind trends may be driven by changing surface roughness and/or stability in different Arctic regions and seasons, by comparing CESM2 experiments with artificially decreased sea ice roughness to the 50 members of the CESM2 Large Ensemble. Our results are important because they show that sea ice loss is driving future changes in meteorological near-surface conditions that can impact vessel-based transportation in the Arctic.
The surface roughness change from sea ice loss drives about 30-60% of the near-surface wind trends in autumn and winter. Thus, the near-surface wind trends are the result of how sea ice loss drives changes in both surface roughness and near-surface atmospheric stability, yet the sea ice mean state and trends are not driven by coupled impacts from surface roughness on near-surface winds or fluxes but from the overall warming trend due to increasing greenhouse gas emissions. Many state-of-the-art Earth system models use a single constant to represent ice roughness, while observed sea ice roughness varies due to ice conditions, including concentration, thickness, ridge fraction, pond fraction, etc. Because the Arctic wind trends do depend on surface roughness, it is important to better understand how surface roughness may change in the future by using more sophisticated and realistic representations of surface roughness in coupled models.