13.2 Dynamical Coupling Between the Middle Atmosphere and Arctic Sea Ice

Thursday, 29 June 2017: 1:45 PM
Salon G-I (Marriott Portland Downtown Waterfront)
Thomas Reichler, University of Utah, Salt Lake City, UT

The downward influence from stratospheric sudden warmings (SSWs) can impact surface weather and may be able to also influence the distribution of Arctic sea ice. Recent research also found evidence for the opposite effect, that Arctic sea ice anomalies influence the atmospheric circulation above. Some even argue that sea ice can impact the stratosphere and modulate the number of SSWs. The combined effects may have the potential for interesting two-way feedbacks between Arctic sea ice and the stratospheric circulation, which we study in this research. To this end, we investigate observations and a very long control integration with a stratosphere resolving climate model from GFDL. We find clear evidence for an impact of stratospheric circulation anomalies on the distribution of Arctic sea ice: SSWs are followed a few weeks later by persistent negative sea ice anomalies, in particular over the Labrador Sea. We also find that SSWs tend to be preceded by negative sea ice anomalies over the Barents and Kara Seas. This result is similar to recent observational and modeling studies, but our analysis leads to a very different interpretation for such a connection. Previous studies argued that positive anomalies in heat fluxes associated with the negative sea ice anomalies increase the stratospheric wave driving and hence the probability for SSWs. However, in our model we find that the sea ice anomalies preceding SSWs are due to forcing of the ocean by the atmosphere, and not the opposite way, casting some doubts on the previous interpretation. In our model, the atmospheric forcing is related to an internally generated wave-number-one pattern in sea level pressure, that not only increases stratospheric wave driving but also leads to anomalous sea ice advection. We conclude that there is a clear downward influence from the stratosphere onto sea ice, but that there is little evidence for an impact of sea ice variability onto the stratosphere.
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