The weakening summer circulation in the Northern Hemisphere mid-latitudes

Abstract

Rapid warming in the Arctic could influence mid-latitude circulation by reducing the poleward temperature gradient. The largest changes are generally expected in autumn or winter, but whether significant changes have occurred is debated. Here we report significant weakening of summer circulation detected in three key dynamical quantities: (i) the zonal-mean zonal wind, (ii) the eddy kinetic energy (EKE), and (iii) the amplitude of fast-moving Rossby waves. Weakening of the zonal wind is explained by a reduction in the poleward temperature gradient. Changes in Rossby waves and EKE are consistent with regression analyses of climate model projections and changes over the seasonal cycle. Monthly heat extremes are associated with low EKE, and thus the observed weakening might have contributed to more persistent heat waves in recent summers.

Spatio-Temporal Linkages between Declining Arctic Sea-Ice Extent and Increasing Wildfire Activity in the Western United States

“…While many of the above-described atmospheric modes of variation also have been linked to increasing wildfire activity in the western United States [21,54,[57][58][59][60], caution must be taken when establishing direct causal linkages between declining ASIE and increasing wildfire activity through correlative analyses. In short, low (high) levels of ASIE perturb atmospheric flow through interactions with latitudinal temperature gradients, which in turn can impact atmospheric thickness, zonal (meridional) flow patterns [12,16] and surface climatic conditions associated with both wildfire and specific modes of variation [21].…”

“…Our understanding of the processes is constantly evolving (e.g., [13,14]) with recent research suggesting that, among others, ASIE is potentially a controlling factor or interacts with (1) the Atlantic multidecadal oscillation (AMO; [14]); (2) the NAO [13,15]; (3) the western Pacific pattern (WP) and El Nino Southern Oscillation (ENSO; [15]); (4) declining summertime total kinetic energy and zonal flow [16]; (5) the Pacific Decadal Oscillation (PDO; [17]); (6) surface temperature extremes [10]; and (7) surface precipitation extremes [18,19]. An example of the evolution of our understanding of the linkages includes studies [13,20], which found that contrary to earlier work based on empirical data [2,5], model simulations show that lower levels of ASIE are associated with reductions in wintertime cold events in Northern Europe, not increases in these events.…”

The 2015 European Heat Wave

“…This might have favored a northward shift of the North Atlantic summer storm track (e.g., Ogawa et al 2012;Dong et al 2013a and2013b;Duchez et al 2016), which would result in reduced precipitation in summer 2015 over central Europe (Supplemental Fig. S12.1g) | Arctic might also be a factor for the 2015 summer heat wave (Coumou et al 2015).…”

More homogeneous wind conditions under strong climate change decrease the potential for inter-state balancing of electricity in Europe

“…State-of-the-art global climate models reveal that changes in zonal wind depend on the temperature structure of the lower atmosphere (Haarsma et al, 2013) and that zonal-mean zonal wind and eddy kinetic energy decline almost linearly in time due to polar amplification (Coumou et al, 2015). There are also natural sources of variability at up to decadal timescales.…”