An Examination of Extratropical Cyclone Sensitivity to Environmental Variability

[摘要] As primary drivers of synoptic-scale midlatitude atmospheric variability, extratropical cyclones (ETCs) are an important influence on the day-to-day weather in the most populated regions of the planet. Given their environmental connections at multiple length scales, the impacts of ETCs in a future climate are difficult to predict. Some facets of a future climate, such as a weaker equator-to-pole temperature gradient, may weaken ETCs, while other factors, such as an increase in atmospheric moisture content, may strengthen ETCs. Separating these effects is complicated by incomplete observational coverage and the nonlinear response of the system to environmental perturbations. Therefore, we use numerical modeling to systematically explore ETC response to changes in environmental characteristics.Improving upon previous unrealistic and unphysical perturbation schemes, we developed a novel scheme for perturbing environmental temperature (as a proxy for moisture) and baroclinicity. Using the Weather Research and Forecasting model, we have run several suites of experiments focused on ETC sensitivity to each environmental characteristic individually. Additionally, we performed the first examination of a bivariate parameter space, combining simultaneous perturbations to environmental temperature and baroclinicity. We find non-monotonic responses in strength due to the increasing effect of moist processes on ETCs with increasing temperature, and interplay between the perturbed environmental characteristics. Additional experiments with a latitudinally-varying, beta-plane Coriolis configuration demonstrate the sensitivity of ETC response to a seemingly small configuration modification. Finally, we examine ETC sensitivity to the inclusion of radiative processes, largely neglected in idealized sensitivity literature.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 impacted 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 interactions with atmospheric water vapor. While not a complete examination of all environmental variables, this suite of simulations demonstrates the need to consider ETC sensitivity to multiple variables simultaneously, as there are a breadth of scales at which ETCs are affected by changes to the Earth’s climate system.

[发布机构] University of Michigan

[效力级别] Atmospheric Science

[关键词] Extratropical Cyclones;Atmospheric Science;Atmospheric;Oceanic and Space Sciences;Science;Atmospheric, Oceanic & Space Science