The Bivariate Sensitivity of Persistent Anomalies to Environmental Temperature and Baroclinicity

Given their frequent association with blocking activity, persistent anomalies (PAs) in geopotential height play a crucial role in defining the midlatitude wave guide. However, their effects are most felt by society when blocking patterns result in high-impact weather – extreme temperature or precipitation events on the order of several days to weeks, such as heat waves, droughts, and flooding. With a large spatial scale and long temporal scale, PAs both exert significant influence on the surrounding environment and are significantly influenced by it. As this environment continues changing with climate change, untangling these influences to understand how PA activity may change in the future becomes an increasingly more complex question. Until now, most work on PA-environmental interaction has focused on the overall impact of climate change on PAs, rather than isolating the separate effects of changes in specific climate variables.

We present a process-based, bivariate examination of PA sensitivity to environmental temperature/moisture and baroclinicity using the Weather Research and Forecasting model in an idealized channel configuration, isolating environmental variables that mirror increasing global temperatures and Arctic amplification. This approach reveals potential interactions between the two variables of interest, and more directly addresses situations in which the existing literature describes competing influences on PAs. Indeed, this is the case with Arctic amplification, wherein a weaker jet stream results in slower propagation speeds (increasing PA activity) and less baroclinic activity (decreasing PA activity by reducing atmospheric variance) – leaving the overall theoretical result unclear. Turning to idealized modeling for more clarity, we first characterize the mean flow in our simulations, before analyzing the sensitivity response of PA frequency, strength, and duration. Using a PA identification algorithm with a constant height anomaly threshold we find that an increase in temperature results in stronger PAs. Finally, we compare the isolated and combined responses of PAs to both temperature and baroclinicity, thus learning more about the underlying dynamics of how climate change may influence PA activity.