Arctic Amplification Weakens the Variability of Daily Temperatures over Northern Middle-High Latitudes

Arctic amplification (AA) reduces meridional temperature gradients (dT/dy) over the northern mid-high latitudes, which may weaken westerly winds. It is suggested that this may lead to wavier and more extreme weather in the midlatitudes. However, temperature variability is shown to decrease over the northern mid-high latitudes under increasing greenhouse gases due to reduced dT/dy. Here, through analyses of coupled model simulations and ERA5 reanalysis, it is shown that consistent with previous studies, cold-season surface and lower-mid troposphere temperature (T) variability decreases over northern mid-high latitudes even in simulations with suppressed AA and sea ice loss under increasing CO2; however, AA and sea ice loss further reduce the T variability greatly, leading to a narrower probability distribution and weaker cold or warm extreme events relative to future mean climate. Increased CO2 strengthens meridional wind (upsilon) with a wavenumber-4 pattern but weakens meridional thermal advection [-upsilon(dT/dy)] over most northern mid-high latitudes, and AA weakens the climatological upsilon and -upsilon(dT/dy). The weakened thermal advection and its decreased variance are the primary causes of the T variability decrease, which is enlarged by a positive feedback between the variability of T and -upsilon(dT/dy). AA not only reduces dT/dy, but also its variance, which further decreases T variability through -upsilon(dT/dy). While the mean snow and ice cover decreases, its variability increases over many northern latitudes, and these changes do not weaken the T variability. Thus, AA's influence on midlatitude temperature variability comes mainly from its impact on thermal advection, rather than on winds as previously thought.