Observed Changes of Poleward Energy Transport for Northern Hemisphere Cool-Season Extratropical Cyclones: A Multi-perspective Eulerian Approach

Diagnosing how global warming has impacted the seasonal poleward transport of heat and moisture, particularly that by Extratropical Cyclones (ETCs), remains an open question. This work uses a multi-perspective Eulerian approach to quantify the change in the role of Northern Hemisphere high-frequency transient eddies (and by proxy, ETCs) in the poleward transport of the largest terms (Dry Static Energy, DSE, and Latent Heat, LH) from 1980 to 2022 during the cool-season (November-March), when ETCs are often stronger and more impactful. Previous studies indicate opposing processes that both enhance and reduce poleward energy transport by transient eddies, resulting from changes in baroclinicity and moisture availability in the atmosphere. Key results of this study indicate a small, yet opposing trend by transients to the statistically-significant increase in the total DSE transport in the subtropics and midlatitudes (26.7% increase in total DSE over the 2001-2022 period), yet a reinforcement by ETCs to the weakening DSE transport past 60° N (15% decrease by tranisents over the same period). In addition to a 10% strengthening of equatorward LH transport from 5-15° N from 2001-2022, a poleward shift is found in the midlatitude location of maximum LH transport at 37° N, which is particularly evident in the Pacific storm track (increase by 23.3% over the same period). In this region, ETCs contribute nearly 48% to the seasonal climatology of LH transport, underscoring the importance of studying how ETCs and associated processes will respond in a warming world.