The following linkage between AA and mid-latitude weather patterns has been hypothesized [1]. Increasing AA weakens the poleward temperature gradient—a fundamental driver of zonal winds in upper levels of the atmosphere—which causes zonal winds to decrease, following the thermal wind relationship [18]. A weaker poleward temperature gradient is also a signature of the negative phase of the so-called Arctic oscillation/Northern annular mode (AO/NAM), in which weaker zonal winds are associated with a tendency for a more meridional flow, blocking, and a variety of extreme weather events in much of the extratropics [19]. Disproportionate Arctic warming and sea-ice loss favor a negative AO/NAM aloft [1, 2, 20, 21] and a Northward migration of ridges in the upper-level flow [1], further contributing to an increased meridional pattern. As the wave amplitude and/or frequency of amplified flow regimes increases, the incidence of blocking becomes more likely [2], which reduces the Eastward propagation speed of the pattern. Consequently, the associated weather systems persist longer in a particular area. Extreme weather events caused by prolonged weather conditions (such as cold spells, stormy periods, heat waves, and droughts), therefore, should also become more likely, as illustrated by recent studies linking these events to high-amplitude planetary waves [22–24]. http://iopscience.iop.org/article/10.1088/1748-9326/10/1/014005
Gelukkig maar.