| In NH winter, the Pacific storm track tends to reach its maximum intensity during early and late winter, leaving a distinct minimum in January, which is known as "midwinter minimum" (MWMIN) of the Pacific storm track. The main objective of this study is to explain the origin of MWMIN from the perspective of dry dynamics. Diagnosing 40-year NCEP/NCAR reanalysis data, we examined the frequency of occurrence of MWMIN and the structural features in the planetary-scale flow associated with MWMIN. The results suggest a hypothesis that a significant enhancement of the barotropic damping relative to the baroclinic growth from early to midwinter is an important contributing factor for MWMIN. This hypothesis is tested with both an idealized quasi-geostrophic two-level model and a relatively realistic primitive equation model. The model results are compared against observations from the perspective of eddy energetics. Remaining questions and their implications are discussed. |
