The seasonal variability of midlatitude storm tracks and their sensitivity to baroclinicity and jet location in an idealized GCM

Observational studies have shown that while baroclinicity over the Pacific ocean reaches its peak in midwinter, transient eddy activity exhibits a distinct minimum during this season, and a maximum in late-fall and early-spring. This behavior has been attributed to different factors, including diabatic effects, reduced seeding over Asia, and upper-level trapping. To explore the seasonal cycle of storm tracks in an idealized moist atmospheric general circulation model (GCM), we implement an idealized seasonal cycle by varying the radiative parameters of the model. Through a series of numerical experiments, we investigate the relation between baroclinicity and the energetics of storm track eddies. It is found that eddy kinetic energy (EKE) in the storm track is sensitive to the position of the jet in the idealized model, and is uncorrelated with the period of maximum baroclinicity. This relation becomes relevant in light of observations, since during midwinter, the intensity of Pacific jet stream has been shown to be negatively correlated with the storm track activity. We further investigate this using NCEP reanalysis data, averaged between the years 1981-2010, which reveals that during these periods of negative correlation, the jet has stronger vertical shear, and is located closer to the equator relative to fall or spring. In addition, the implications of other factors, such as diabatic heating, in the seasonal cycle of the Pacific storm track will be discussed.