Friday, September 21, 2012

Arctic Amplification and Midlatitude Weather

In the previous post, we discussed how the summer sea-ice extent is declining in the Arctic.  This sea-ice decline is simultaneously a result of and a contributor to enhanced warming of the Arctic relative to other regions, which is sometimes referred to as Arctic Amplification.  Arctic Amplification is produced by increased greenhouse gas concentrations combined with feedbacks such as increased absorption of solar radiation due to declining snow and ice cover.

An area of growing scientific interest concerns the implications of Arctic Amplification for midlatitude weather.  More rapid warming of the Arctic compared to the lower latitudes leads to a decrease in the average temperature contrast in the midlatitudes.  The strength of the upper-level flow is proportional to this temperature contrast.  Therefore, one would expect upper-level flow to weaken (on average) in response to Arctic Amplification.  

Recently, Francis and Vavrus (2012) proposed that this effect could contribute to more persistent weather patterns in the midlatitudes.  In particular, as the upper-level flow weakens, waves (i.e., troughs and ridges) tend to progress more slowly eastward.  They also suggest that the amplitude of these waves has increased due to Arctic Amplification, with upper-level ridges extending farther into the high latitudes, leading to higher amplitude upper-level waves that tend to move more slowly.

How the midlatitude flow will respond to global warming is a critical issue for projecting future regional climate change.  There is arctic amplification, but also other aspects of the climate system that are changing in ways that could affect the midlatitude flow.  This is an area of growing interest and research and fertile ground for motivated graduate students looking for a good thesis project.


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  2. Hi Jim, its funny that you bring this up as we had the exact same discussion in our Physical Meteorology class since we were reviewing radiation budgets. It was mentioned in this discussion that a lot of climate models don't necessarily include changing albedo (its simply kept constant) from the melting of the ice caps thus, you never get the weakening of the general circulation (or as you termed it, the weakening of the upper level flow). I found this intriguing since this is something that you would think should be included in all climate models! I was wondering if you had any knowledge whether this is true or not.

    Anyways great post, certainly makes for good food for thought!

    1. Derek:

      I don't work enough with climate models to know the answer to your question. Based on my work with weather models, it could be that the albedo of ice is fixed, but once the ice is gone, the surface albedo becomes that of the underlying land surface. Because of the former, the changes in the albedo of the ice due to changes in ice-grain size, dust and soot deposition, and other factors would not be included, but because of the latter, the dramatic change in albedo when the snow or ice is fully ablated is considered.

      If you do some digging into the literature, I suspect you can find an answer to your question. You might start with the Chapter 8 of the IPCC AR4, Working Group I report (, see cryospheric section) and references therein. Note that the runs being done for the forthcoming AR5 may contain updated parameterizations.