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.