ENSO and atmospheric energetics along the tropical storm track

Warm SST anomalies over the Central-Eastern Pacific SST are associated with the strengthening and eastward stretching of the monsoon trough and westerly jet stretching from Bay of Bengal to the western North Pacific (WNP) along 5°-15°N. During this SST warm period, the frequency and intensity of tropical storms over the WNP also increase. The formation of the tropical storm extends southeastward. The interannaul variability of this large-scale circulation and tropical storm during July to September are investigated by the energetic diagnostic tool.

Composites of kinetic energy over the WNP indicate that the mean kinetic energy (MKE) and eddy kinetic energy (EKE) are larger during warm years than during cold years. With coincidence of the eastward extension of the monsoon trough, westerly jet, and the formation of tropical storm, the maximum axes of both of mean kinetic energy and eddy kinetic energy extend eastward during warm years. The westerly jet is maintained by an enhanced mean baroclinic energy conversion. The increase of EKE along the tropical storm track, during warm years, is contributed by both the barotropic energy conversion and baroclinic energy conversion. The stronger barotropic conversion occurs in the low levels and is mainly related to enhancement of the low-level westerly jet. Contrary to the barotropic energy conversion, the baroclinic energy conversion maximizes in the upper levels. This indicates that during ENSO years, the enhancement and eastward extension of monsoon trough and westerly jet at low levels, and the strengthened convection at upper levels provide a favorable condition for the growth of transient eddies including tropical storms through eddy barotropic and baroclinic energy conversion.