Interactions between Summer Intraseasonal Oscillations and
Synoptic-scale Disturbances over the Western North Pacific
Pang-chi Hsu and Tim Li
LFBS to Eddy
ISO to Eddy
Eddy to ISO
(Left) 850-hPa barotropic energy conversion between LFBS and eddy averaged over July-September. 850-hPa barotropic energy
conversion between ISO and eddy during the ISO (Middle) active and (Right) suppressed phase. Units: 10-5m2/s3.
The role of scale interactions in the eddy kinetic energy (EKE) budget during the wet and dry
phases of the intraseasonal oscillation (ISO) was examined with a newly constructed eddy
energetics diagnostic tool that separates the EKE of the ISO from that of the low-frequency
background state (LFBS, with periods longer than 90 days). In boreal summer, synoptic eddies
take on kinetic energy from LFBS regardless of the ISO phase. During the moist ISO phase, the
eddies extract energy from the ISO. This positive barotropic energy conversion results from eddyinteraction with the low-level cyclonic and convergent/confluent ISO flows. During the dry ISO
phase, the synoptic eddies lose kinetic energy to the ISO flow. This negative barotropic energy
conversion results from eddy-interaction with the anticyclonic and divergent/diffluent ISO flows.