The Intraseasonal Oscillation and the Energetics of Summertime Tropical Western North Pacific Synoptic-Scale Disturbances

Abstract

Abstract The tropical intraseasonal oscillation (ISO) causes variations in the large-scale flow over the western North Pacific during June–August that strongly impact the energetics of tropical depression (TD)-type disturbances. An energetics analysis is conducted with NCEP–NCAR reanalysis data during June–August of 1979–2001. Composite TD-type disturbance perturbation kinetic energy (PKE) is significantly higher during ISO 850-hPa westerly periods than during ISO 850-hPa easterly periods. ISO westerly periods are associated with enhanced barotropic conversion and enhanced perturbation available potential energy (PAPE) to PKE conversion. ISO easterly periods are characterized by diminished TD-type PKE, negligible barotropic conversion, and weakened PAPE to PKE conversions, as compared to composite TD-type disturbances during ISO westerly periods and the entire June–August record. Barotropic conversion accounts for a larger fraction of the PKE generation during ISO westerly periods than during the entire J...