Storm Track Response to Uniform Global Warming Downstream of an Idealized Sea Surface Temperature Front

The future evolution of storm tracks, their intensity, shape, and location, is an important driver of regional precipitation changes, cyclone-associated weather extremes, and regional climate patterns. For the North Atlantic storm track, Coupled Model Intercomparison Project (CMIP) data indicate a tripole pattern of change under the RCP8.5 scenario and no clear poleward shift but rather a downstream extension and local intensification. In this study, the tripole pattern is for the first time qualitatively reproduced by simulating the change of a storm track generated downstream of an idealized sea surface temperature (SST) anomaly, which mimics the land-sea contrast and Gulf Stream SST front, under uniform warming on an aquaplanet.

The simulated tripole pattern consists of reduced eddy kinetic energy (EKE) upstream and equatorward of the SST anomaly, extended and poleward shifted enhanced EKE downstream of the SST anomaly, and a regionally reduced EKE increase at polar latitudes. In the absence of the idealized SST anomaly, in contrast, the storm track exhibits a poleward shift but no tripole pattern. A detailed analysis of the EKE and eddy available potential energy (EAPE) sources and sinks reveals that the changes are locally driven by changes in baroclinic conversion rather than diabatic processes, in contrast to argument based solely on thermodynamics. However, globally the change in baroclinic conversion averages to zero; thus the observed global EAPE increase results from diabatic generation, in agreement with thermodynamic arguments. Stationary waves amplify above the SST anomaly, as well as up- and downstream of it, in agreement with theory, and further shape the reduction of EKE poleward of the front. Finally, automated cyclone tracking is used to illuminate changes in cyclone life cycle characteristics under warming in the vicinity and absence of the SST front.

Literature: Storm track response to uniform global warming downstream of an idealized sea surface temperature front. Schemm, S., Papritz, L., & Rivière, G. (2022). Weather and Climate Dynamics, 3(2), 601-623.