Constraining the Varied Response of Northern Hemisphere Winter Circulation Waviness to Climate Change.

While a large latitudinal displacement of the westerly jet brings about disproportionate socioeconomic impacts over Northern Hemisphere midlatitude continents, it is not well understood as to whether the winter circulation will become wavier or less in response to climate change. Here, using observations and large ensembles of climate models, we show that changes in atmospheric waviness can be estimated from the optimal structures of the westerly jet for wavier circulation, which are obtained from an advection‐diffusion model. Thus, the changes in westerly jet structure in climate models under climate change provide a physical constraint on changes in atmospheric waviness, indicating that the North Atlantic wave activity will experience a robust decline in a warmer climate, while future North Pacific wave activity is obscured by model uncertainty rather than internal variability. These findings highlight the changes to jet stream structure as a constraint for regional circulation waviness in a changing climate. Plain Language Summary: A large latitudinal meandering of Northern Hemisphere winter circulation can induce stagnant weather that causes severe impacts on densely populated East Asia, Western North America, or Western Europe, yet whether the winter circulation will become wavier or less under climate change remains uncertain. Here we analyze observations and large ensembles of climate models and show that changes to atmospheric wave activity under climate change are largely constrained by changes to zonal advecting wind for the Lagrangian motion of air parcels in an advection‐diffusion model. This constraint further indicates a consistent decline in future waviness over the North Atlantic, while changes to future wave activity over the North Pacific are uncertain, due to model uncertainty rather than internal variability of the climate system. Key Points: Changes in atmospheric waviness can be roughly estimated by changes in zonal advecting wind in an advection‐diffusion modelChanges in the optimal structure of jet stream help constrain regional circulation waviness in a changing climateModel results suggest future waviness will robustly decline in North Atlantic but is less clear in North Pacific due to model uncertainty [ABSTRACT FROM AUTHOR]