Characteristics of Barotropic-Baroclinic Interactions during the Formation of Blocking Events in the Pacific Region.

Abstract

In this study, characteristics of barotropic-baroclinic conversions of kinetic energy C(K s ,K m ) are examined for atmospheric blocking, using the NCEP/NCAR reanalysis data. The energetics analysis was based on the formula derived originally by Wiin-Nielsen (1962). As a result of case studies and composite analysis, we found that there were two maxima of C(K s ,K m ) located along the western and eastern flanks of the blocking ridge, indicating that the baroclinic kinetic energy is converted to the barotropic kinetic energy in those regions. On the other hand, for a non-blocking case, where a ridge had amplified rapidly but not evolved into the blocking, the interactions C(K s ,K m ) indicate only one maximum along the western flank of the ridge. Around the blocking region, the nondivergent part of C(K s ,K m ) was a large contributor, which is associated with temperature advection. As a meridional flow is further amplified, the enhanced temperature advection associated with the meridional flow induces larger conversion of C(K s ,K m ). Because a blocking flow is characterized by an amplified meridional flow, especially for the barotropic component, the barotropic-baroclinic interactions C(K s ,K m ) appear to play an important role for the formation of a blocking.