Interdecadal Variation Of Equatorial Rossby Waves During Boreal Summer

The equatorial Rossby waves(ERWs)are a westerly component of Convectively coupled equatorial waves.Their activities have an important impact on the weather and climate in the tropics and even in the world.The research results can provide scientific basis for improving the simulation performance of the numerical model for the tropical atmospheric waves and improving the short-term climate prediction level of China for the tropical areas,which has important practical value.The main methods used are spatiotemporal spectrum analysis,wavenumber-frequency-filtered,empirical orthogonal function analysis,synthesis analysis,correlation analysis.The interdecadal variation of summer equatorial Rossby waves(ERWs)intensity and its main drivers are revealed from an analysis of zonal winds(NCEP),interpolated outgoing longwave radiation(NOAA),and monthly mean sea surface temperature data(Met Office Hadley Centre)and the atmospheric general circulation model ECHAM version 6.The main methods used are spatiotemporal spectrum analysis,wavenumber-frequency-filtered,empirical orthogonal function analysis,synthesis analysis,correlation analysis.An index of ERWs intensity(ERWs-II)is defined using the principal components associated with the two leading modes identified from an empirical orthogonal function analysis of wavenumber-frequency-filtered OLR anomalies during 1979-2018(JJAS).Analysis of ERWs-II shows that ERWs intensity underwent significant interdecadal variation around 1995/1996,with ERWs intensity being relatively weak before 1995,but stronger after 1996.The configuration of Pacific Decadal Oscillation(PDO),Atlantic Multidecadal Oscillation(AMO),and Indian Ocean Basin Mode(IOBM)mainly accounts for the interdecadal variation of summer ERW intensity during different phases.Under the synergistic effect of global sea surface temperature warming,when the PDO is in its negative phase,and the AMO and IOBM are in their positive phase,ERW intensity is stronger at the interdecadal time scale,and vice versa.The observation results are verified by numerical test of ECHAM6 model.Modeling results confirm the associated physical processes driving this variation.The anomalous state of divergent wind caused by the coordinated changes of PDO,AMO and IOBM in the context of global warming When the anomalous state of divergent wind resonates with its climatic state in the same phase,the intensity of equatorial Rossby waves is strengthened.The anomalous state of divergent wind and its climatic state are in the same resonance,which is the main reason for the interdecadal variation of the equatorial Rossby wave intensity in the boreal summer.