A Further Investigation of the Decadal Variation of ENSO Characteristics with Instability Analysis

Based on instability theory and some former studies, the Simple Ocean Data Assimilation (SODA)data are analyzed to further study the difference between the propagation of the ENSO-related oceanic anomaly in the off-equatorial North Pacific Ocean before and after 1976. The investigation shows that after 1976 in the off-equatorial North Pacific Ocean, there is a larger area where the necessary conditions for baroclinic and/or barotropic instability are satisfied, which may help oceanic anomaly signals propagating in the form of Rossby waves to absorb energy from the mean currents so that they can grow and intensify.The baroclinic energy conversion rate in the North Pacific after 1976 is much higher than before 1976,which indicates that the baroclinic instability has intensified since 1976. From another perspective, the instability analysis gives an explanation of the phenomena that the ENSO-related oceanic anomaly signal in the North Pacific has intensified since 1976.