Deciphering Mean Flow-Eddy Interaction in Pacific-North American Teleconnection Linked to Storm Tracks at Subseasonal Time Scales

The features of large-scale atmospheric circulations, storm tracks, and the mean fl ow-eddy interaction during winter Paci fi c-North American (PNA) events are investigated using National Centers for Environmental Prediction- National Center for Atmospheric Research (NCEP-NCAR) reanalysis data at subseasonal time scales from 1979 to 2022. The day-to-day variations of storm-track activity and streamfunction reveal that storm-track activity varies along the evolution of mean fl ow. To better understand storm-track variability with the mean fl ow-eddy interaction, further exploration is made by analyzing local energy energetics. The changes in horizontal and vertical baroclinic energy conversions from background fl ow correspond to the storm-track anomalies over the North Paci fi c, indicating that the anomalies in storm tracks are due to the anomalous mean fl ow associated with PNA patterns impacting energy conversion through mean fl ow-eddy interaction. Eddy feedback driven by vorticity and heat fl uxes is analyzed. This provides a concrete illustration of how eddy feedback serves as a positive factor for the upper-tropospheric circulation anomalies associated with the PNA pattern. SIGNIFICANCE STATEMENT: The background fl ow plays a crucial role in governing storm-track dynamics. Our emphasis is on the Paci fi c storm tracks (PST) and their relation to Paci fi c-North American (PNA) patterns at subseasonal time scales. We unveil the relationship between anomalies of PST and PNA patterns using local energetics and eddy feedback on a day-by-day basis. It is noteworthy that the evolution of anomalous storm tracks during PNA events is the manifestation of mean fl ow-eddy interaction. Additionally, we provide detailed con fi rmation of the impact of anomalous storm tracks on large-scale anomalies associated with the PNA pattern.