The Impact Of ENSO On IOD Skewness And The Causes Of Model Simulation Bia

When the Indian Ocean Dipole(IOD)occurs,it will have an important impact on its regional and global climate.Especially under the influence of the asymmetry(skewness)of IOD intensity,the impact of IOD on climate is also asymmetricextreme and positive IOD events often cause more serious disasters.Therefore,strengthening the research on IOD skewness has important scientific value for disaster prevention and mitigation.At present,the research on IOD skewness focuses on the local air-sea feedback effect in the Indian Ocean,and a large number of studies point out that El Ni(?)o-Southern Oscillation(ENSO)dominates the IOD variability through tropical atmospheric teleconnection,so it is necessary to further strengthen the research on the impact of ENSO on IOD skewness.Using reanalysis and model data,this paper discusses the modulation effect of ENSO on IOD bias by analyzing the IOD events corresponding to ENSO events of different intensities.The simulation status of IOD skewness in the model and the causes of simulation deviation are analyzed.The major conclusions can be summerized as follows:(1)A dipole structure of SST skewness in the Indian Ocean is observed and a negative value in the east pole during boreal autumn,concurrent with a positive SST skewness in the equatorial central-eastern Pacific.A nonlinear relationship is displayed between the IOD and ENSO and extreme positive IOD events tend to be accompanied by strong El Ni(?)o events.The composites of IOD associated SST and wind anomalies during strong El Ni(?)o and La Ni(?)a exhibit the positive asymmetric distributions.In contrast,the SST and wind anomalies of IOD display quasi-symmetric features in the spatial pattern and intensity between weak El Ni(?)o and La Ni(?)a events.As a result,ENSO could modulate IOD skewness in a nonlinear way via asymmetric remote atmospheric response.Positive IOD skewness is mainly attributed by the strongly positive IOD events that could be largely modulated by strong El Ni(?)o events.(2)In the models with good simulation of IOD skewness,there is a certain nonlinear relationship between ENSO and IOD,and the correlation is high in El Ni(?)o phase.Consistent with the observation,IOD shows significant asymmetric characteristics during strong El Ni(?)o and La Ni(?)a events.The intensity of IOD during weak El Ni(?)o and La Ni(?)a events shows quasi-symmetric characteristics.Strong El Ni(?)o events affect IOD skewness by modulating IOD intensity.Because ENSO skewness is better simulated,IOD skewness is also better simulated.In the models with poor simulation of IOD skewness,the correlation between ENSO and IOD is poor,or the correlation between ENSO and IOD is high during La Ni(?)a event.The skewness is caused by the extreme negative IOD events caused by the extreme La Ni(?)a events.Because the strong positive IOD events caused by the strong El Ni(?)o events cannot be simulated,the simulation bias of IOD skewness is caused.The simulation bias of ENSO intensity can also cause bias in the simulation of the Indian Ocean climatological sea temperature,zonal wind and thermocline depth,which makes the air-sea conditions of the Indian Ocean and the Pacific Ocean more conducive to the occurrence and development of La Ni(?)a and its corresponding negative IOD events in the poor models.Therefore,the bias of IOD skewness simulation in the poor model is mainly caused by the bias of ENSO skewness simulation.