Assessing the Impacts of Climate Variability on Extratropical Cyclone Development and Strength

Given their extraordinary influence on mid-latitude weather conditions, understanding how the impacts of extratropical cyclones (ETCs) might differ in various cyclogenetic environments is crucial to understanding the effects of the Earth’s changing climate system on many of the most populated areas of the planet. However, projecting such changes is complicated by the many facets of climate change, which provide contradicting signals as to how ETC strength may vary in the future. Examining the responses of ETCs to changes in climate through use of observational data is difficult, given its incomplete coverage. Nonlinear responses to environmental perturbations limit the applicability of a purely theoretical approach. Numerical modeling provides a virtual laboratory that can be used to systematically explore ETC responses to changes in environmental characteristics.

Improving upon previous ETC sensitivity analysis methodologies, we develop a novel scheme for perturbing environmental temperature (as a proxy for moisture) and baroclinicity. Using the Weather Research and Forecasting model in an idealized configuration, we run several univariate ETC sensitivity experiments, as well as bivariate experiments that combine perturbations to both environmental moisture and baroclinicity. We find non-monotonic responses in cyclone strength due to the increasing effect of moist processes on ETCs with increasing temperature, and the interplay between the perturbed environmental characteristics. Additionally, we examine ETC sensitivity to the inclusion of radiative processes, often overlooked in previous considerations.

These experiments reveal that extratropical cyclone development can be divided into three regimes: baroclinic, diabatically-limited, and diabatically-driven. As environmental temperature warms, ETCs stray from the canonical development mechanisms of the baroclinic regime and are increasingly affected by diabatic heating and the formation of diabatic Rossby vortices. The inclusion of radiative processes consistently increases the strength of ETCs, primarily affecting development through radiative interactions with atmospheric water vapor. This suite of simulations also demonstrates the need to consider ETC sensitivity to multiple variables simultaneously to obtain a more complete understanding of the effect of climate change on dynamic weather systems.