Role of Mean States on Atmospheric Responses to High-latitude thermal forcing and Arctic Warming

The study investigated the atmospheric responses to high-latitude thermal forcing and its implication in the Arctic amplification. We found an important role of mean state in affecting how midlatitude waves respond to high-latitude warming by conducting a set of experiments with three different idealized control climates: a perpetual equinox-like climate, a perpetual winter-like climate, and a perpetual summer-like climate. Our result suggests that the background stability affects both the time scale and magnitude of atmospheric responses to high-latitude heating.
The background stability affects the structure of the tropospheric warming, leading to distinct responses of midlatitude waves. Our finding shows that the surface trapped warming in a cold climate lead to a relatively more unstable lower-troposphere, resulting to a weak change in baroclinicity and a muted eddy momentum flux response in the upper level. On the other hand, the extending warming in the warm climate leads to significant decrease in baroclinicity due to a strong decrease in meridional temperature gradient and a weak decrease in stability.
Subsequently, we analyze simulations involving abrupt CO2 forcing, utilizing data sourced from Liang et al. (2022). Our analysis reveals enhanced wave generation near 60N and 65S in specific seasons in response to varying CO2 concentrations. We suggest that these anomalies result from the structure of the warming and corresponded stability changes. Given the close relationship between baroclinicity, upper-level eddy momentum flux, and midlatitude westerlies, we suggest that the mechanism of stability change and its effect on wave generation in our study will improve the understanding of the changes in midlatitude waves and westerlies in the future.