The observed losses in Arctic sea ice during the past decades have been linked to the relaxation of poleward thickness gradients (thus weakened zonal winds) and a slower eastward progression of Rossby waves in the upper-level, which help promote prolonged extreme weather conditions, such as heat waves, within the mid-latitudes (e.g., Francis & Vavrus, 2012). However, the background zonal wind and vertical wind shear are important ingredients for tornado formation. An article published in npj Climate and Atmospheric Science (Trapp & Hoogewind, 2018) further explored this idea to report a robust positive correlation between U.S. tornado activity and Arctic sea-ice extent (SIE) in boreal summer during 1990 – 2015. This statistical relationship is supported by the presence of anomalous regional circulation and storm track that are unfavorable for tornado-bearing thunderstorm formation when SIE is low.
Figure 3 from Trapp & Hoogewind (2018): Probability of a tornado day within the U.S. as a function of calendar day, for tornadoes rated a F/EF3 and greater, and bF/EF1 and greater. The green curve represents a 26-y mean, with the lighter-green shading indicating the daily 95% confidence intervals determined from 10,000 bootstrapped resamples. The blue (red) curve shows the 10-y mean from 1990–1999 (2006–2015). A 15-day Gaussian filter was applied to the raw probabilities over each period. Note that the scales of the y-axis in (a) and (b) are different.
Trapp, R. J., & Hoogewind, K. A. (2018). Exploring a possible connection between US tornado activity and Arctic sea ice. npj Climate and Atmospheric Science, 1(1), 14. https://www.nature.com/articles/s41612-018-0025-9.
Francis, J. A., & Vavrus, S. J. (2012). Evidence linking Arctic amplification to extreme weather in mid‐latitudes. Geophysical Research Letters, 39(6). https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012GL051000.