8.6 The Atmospheric Response to Extratropical Ocean Warming Induced By Arctic Sea Ice Loss

Wednesday, 28 June 2017: 11:45 AM
Salon F (Marriott Portland Downtown Waterfront)
Paul J. Kushner, Univ. of Toronto, Toronto, Canada; and R. Blackport

The recent dramatic reduction in Arctic sea ice has motivated a large number of studies that model the atmospheric general circulation response to sea ice loss. Most of these studies force an atmospheric general circulation model (AGCM) with prescribed sea ice loss while keeping sea surface temperatures (SSTs) fixed (e.g Deser et al. 2010). These fixed SST experiments eliminate potentially important thermodynamic and dynamical feedbacks in the coupled ocean atmosphere system. This has motivated recent studies to examine the impact that ocean coupling has on the hemispheric and global-scale response to sea ice loss. Recent work of Deser and others shows that coupling to a dynamical ocean enhances warming in the Arctic mid-troposphere and tropical upper-troposphere (a so-called “mini global warming”) and amplifies by about 50% the atmospheric circulation response. The mechanisms governing this amplification are poorly understood, in light of previous work suggesting that the circulation response to the mini global warming in the tropics should oppose the Arctic amplification response driven by sea ice loss.
In this study, we hypothesize that extratropical ocean warming caused by sea ice loss but located away from the sea ice loss region is an important driver of enhanced Arctic mid-troposphere warming and the associated amplified atmospheric circulation response. This is tested in two ways. We first impose in an AGCM the extratropical SST warming associated with sea ice loss from coupled model experiments, separately from sea ice loss itself, and find that this drives Arctic free tropospheric warming in winter. Next, we estimate the direct impact of sea ice loss on oceanic SSTs in the absence of tropical atmospheric adjustment, using a two parameter pattern scaling technique recently developed by the authors. When this new midlatitude SST pattern is imposed as a separate forcing in the AGCM, it also enhances Arctic free tropospheric warming. The results suggest that Arctic sea ice loss can directly drive midlatitude oceanic warming, which in turn can enhance Arctic free tropospheric warming, even in the absence of tropical adjustment.
- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner