Preliminary Study Of ENSO Asymmetry

In this paper, the relationship between the ENSO asymmetry and nonlinear dynamicalheating, and the linear dynamical heating is examined. In addition, the oceanequatorial Kelvin wave plays an important role in the dynamic conditions of thePacific. The relationship between the ocean Kelvin wave and ENSO asymmetry isalso studied.According to the non-linear heating theory proposed by Jin (2003), nonlineardynamical heating has an important role in the ENSO asymmetry. Nonlineardynamical heating enhance the sea surface temperature anomaly growth during ElNino development stage and suppress the reduction of sea surface temperatureanomaly during La Nina development stage, which results in different sea surfacetemperature anomaly amplitude in the different phases of ENSO. The nonlineardynamic heating for a contribution of ENSO asymmetry is examined and get thefollowing conclusions: First, ENSO asymmetry has a phase-locking and reachmaturity during winter just as ENSO does. Second, the nonlinear dynamical heatingpeaked ahead of the sea surface temperature anomalies, and can be seen as the causeof sea surface temperature anomalies. Third, the zonal component of nonlineardynamic heating is a major contributor of ENSO asymmetry. Fourth, differentsubsurface depth has little influence in the vertical nonlinear dynamic heatingcalculation. Fifth, there is little difference the nonlinear dynamical heating calculationwith different region choice.The effect of the linear dynamical heating on ENSO asymmetry is not studied in Jin’s(2003) article. In this paper, the linear dynamical heating was calculated and itsinfluence on ENSO asymmetry is analyzed: First, meridional component plays amajor role in the whole linear dynamical heating. Second, linear dynamical heatinghas a role in ENSO asymmetry and zonal component of the linear dynamical heatingworks for the asymmetry of ENSO. Third, both Linear dynamical heating andnonlinear dynamical heating are work for the ENSO asymmetry by suppressing the reduction of sea surface temperature anomaly during La Nina developmentstage. Fourth, latitudinal gradient of the mixed layer temperature anomalies and mixedlayer velocity anomalies are the two factors which control the ENSOasymmetry. Equatorial Kelvin waves lead the change of latitudinal gradient of themixed layer temperature anomalies, thus they havean effect on ENSO asymmetry.