How Strong Is Influence of the Tropics and Midlatitudes on the Arctic Atmospheric Circulation and Climate Change

Relaxation experiments with the atmosphere model from European Centre for Medium-range Weather Forecasts are analyzed to understand influence of lower latitudes (south of about 52 degrees N) on climate variability and change over the Arctic region. Interannual variability of the Arctic troposphere is impacted strongly by both the tropics and the midlatitudes. In general, the link in winter is stronger than that in summer. Furthermore, the tropics and midlatitudes have different preferred pathways by which they influence the Arctic. Trend analysis suggests that winter surface warming trends over the Arctic are driven strongly by the local sea ice-atmospheric interaction. Warming at higher altitudes is strongly tied to remote non-Arctic drivers, with some local amplification. Summer warming trends in northeastern Canada and Greenland are driven strongly by sea surface temperature/sea ice changes and partly by the tropics. The summer warming in northern Europe and western Russia is more strongly driven by the midlatitudes. Plain Language Summary This study analyzes model output from relaxation experiments, in which the atmosphere at lower latitudes is nudged toward reanalysis data, to understand influences of tropics and midlatitudes on the Arctic atmosphere in terms of variability and trends. Our results demonstrate that the Arctic atmospheric circulation in terms of interannual variability can be relatively well constrained by lower latitudes. Generally, lower-latitude forcing of the Arctic is stronger in winter than in summer. However, the Arctic temperature variability is less well constrained, owning possibly to poorly constrained local cloud/radiation feedback. In terms of the recent warming trends in the Arctic region, the surface warming is more strongly related to the local sea ice-atmosphere interaction during winter. The warming at higher altitudes is strongly driven by remote processes. The summer warming is located mainly over the land areas and the driving factors are region dependent.