Abstract
The drivers of rapid Arctic climate change—record sea ice loss, warming SSTs, and a lengthening of the sea ice melt season—compel us to understand how this complex system operates and use this knowledge to enhance Arctic predictability. Changing energy flows sparked by sea ice decline, spotlight atmosphere-surface coupling processes as central to Arctic system function and its climate change response. Despite this, the representation of surface turbulent flux parameterizations in models has not kept pace with our understanding. The large uncertainty in Arctic climate change projections, the central role of atmosphere-surface coupling, and the large discrepancy in model representation of surface turbulent fluxes indicates that these processes may serve as useful observational constraints on projected Arctic climate change. This possibility requires an evaluation of surface turbulent fluxes and their sensitivity to controlling factors (surface-air temperature and moisture differences, sea ice, and winds) within contemporary climate models (here Coupled Model Intercomparison Project 6). The influence of individual controlling factors and their interactions is diagnosed using a multi-linear regression approach. This evaluation is done for four sea ice loss regimes, determined from observational sea ice loss trends, to control for the confounding effects of natural variability between models and observations. The comparisons between satellite- and model-derived surface turbulent fluxes illustrate that while models capture the general sensitivity of surface turbulent fluxes to declining sea ice and to surface-air gradients of temperature and moisture, substantial mean state biases exist. Specifically, the central Arctic is too weak of a heat sink to the winter atmosphere compared to observations, with implications to the simulated atmospheric circulation variability and thermodynamic profiles. Models were found to be about 50% more efficient at turning an air-sea temperature gradient anomaly into a sensible heat flux anomaly relative to observations. Further, the influence of sea ice concentration on the sensible heat flux is underestimated in models compared to observations. The opposite is found for the latent heat flux variability in models; where the latent heat flux is too sensitive to a sea ice concentration anomaly. Lastly, the results suggest that present-day trends in sea ice retreat regions may serve as suitable observational constraints of projected Arctic warming.
Highlights
Sea ice and its overlying snowpack shape energy flows through the Arctic by reflecting the majority of the solar radiation in the sunlit months and inhibiting the Arctic Ocean and atmosphere from exchanging heat, moisture and momentum year-round (e.g., Screen et al, 2013; Vihma, 2014; Boisvert et al, 2015b; Taylor et al, 2018)
We address this hypothesis by 1) evaluating the SHF and linear response of SHF (LHF) climatological distribution in Coupled Model Intercomparison Project 6 (CMIP6) models against observations, 2) comparing observed and simulated SHF and LHF trends within sea ice retreat regimes, 3) analyzing SHF and LHF sensitivities to controlling factors, and 4) analyzing relationships with projected Arctic warming
The central Arctic is characterized by a broad region of negative SHF and LHF values that contribute to the Arctic average SHF and LHF values: −31.8 ± 5.19 W m−2 and −3.1 ± 1.88 W m−2, respectively (Table 2 and 3)
Summary
Sea ice and its overlying snowpack shape energy flows through the Arctic by reflecting the majority of the solar radiation in the sunlit months and inhibiting the Arctic Ocean and atmosphere from exchanging heat, moisture and momentum year-round (e.g., Screen et al, 2013; Vihma, 2014; Boisvert et al, 2015b; Taylor et al, 2018). Arctic sea ice has melted and satellite monitoring of sea ice extent has shown that the summer minimum has decreased at a rate of ~14% per decade over the past 4 decades (Cavalieri and Parkinson, 2012; Stroeve and Notz, 2018). From 2009 to 2020, the Arctic saw 11 out of the lowest 13 September sea ice extents of the satellite record. Arctic sea ice extent is decreasing in all months, with the most rapid declines occurring since the early 2000s (Parkinson and DiGirolamo, 2016). In addition to declining sea ice extent, the totality of the changing conditions in the Arctic, including a warming of SSTs and a lengthening of the sea ice melt season, contribute to increases in evaporation and turbulent fluxes In addition to declining sea ice extent, the totality of the changing conditions in the Arctic, including a warming of SSTs and a lengthening of the sea ice melt season, contribute to increases in evaporation and turbulent fluxes (e.g. Steele et al, 2008; Markus et al, 2009; Stroeve et al, 2014; Boisvert et al, 2015a; Taylor et al, 2018; Boeke et al, 2021)
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