The researchers suggest that when solar activity is low the winter jet stream over the North Atlantic is more likely to get blocked. (Which means vast tongues of cold arctic air stretch far to the south, and someone somewhere, gets freaky and not-nice weather.)
2014 coldest since 1912.
What caused the “Polar Vortex” in 1912?
when solar activity is low = low sunspot count
It turns out that the Sun's magnetic field is in decline,
leading to low or zero sunspot count
last time this occurred there was a mini ice age that lasted 400 years, 1350 to 1750.