Linking Instantaneous and Climatological Perspectives on Eddy-Driven and Subtropical Jets

The distinction between eddy-driven and subtropical jets is conceptually important and well-founded based on different driving mechanisms and dominant types of variability. This climatological perspective may be augmented by consider-ing instantaneous maxima in the wind field and linking these to the time-mean jets. Inspired by EOF and cluster analyses to ex-plore the variability in jet occurrences, we propose a straightforward framework that naturally distinguishes subtropical from eddy-driven jets in instantaneous data. We document that for most ocean basins, there is a clear bimodality in instantaneous jet occurrences in potential temperature-wind speed space. The two types of jets in this phase space align well with the conceptual expectations for subtropical and eddy-driven jets regarding their vertical structure as well as their regional occurrence. Interest-ingly, the bimodality in phase space is most pronounced in the western North Pacific during winter. The climatological jet in this region is typically regarded as "merged," resulting from a mixture of thermal driving and eddy driving. Our results clarify that the strongest instantaneous jets in this region are classified as subtropical, with eddy-driven jets occurring in close proximity to the climatological mean jet, though weaker and slightly more poleward. We also show that the regions of climatological tran-sition from predominantly subtropical to predominantly eddy-driven jets are just downstream of the strongest climatological jets.