Wind Effect On Sea Level Variation In Tropical Pacific Ocean During Two Types Of El Ni(?)o Events

Sea level variations in the tropical Pacific Ocean (TPO) during two types of ElNi o events are analyzed by AVISO altimeter data. Based on the Physical processesmodel, the contribution of wind field is evaluated during the evolution of the twotypes of El Nino events in the east off the Philippine coast (EOP). Then, combinedwith the ROMS model, an atmosphere and ocean mechanism which interprets the sealevel evolution in the two types of El Ni o events is given.The significant interannual signal is obtained by stochastic dynamic method inthe TPO. The interannual variations map spatial non-uniform features with twoprominent periods at30(quasi-biennial) and52months, which account for60%among the seven periods. The amplitudes of quasi-biennial mainly locate in the EOPand the equatorial Pacific. The other amplitudes located in the eastern equatorialPacific, and the east off the Philippine and New Guinea coast.With statistical SSTA in the TPO,21El Ni o events have been found in the past60years, including11Eastern-Pacific (EP) El Ni o events and the alternating10Central-Pacific (CP) El Ni o events. It is found that the CP El Ni o events haveoccurred frequently and comparably in the last two decades.The composite Sea Level anomaly (SLA) illustrates the remarkable discrepancygeographically. A “shuttle” pattern of the positive anomaly towers in centralequatorial Pacific, with the largest value nearly9cm, in the CP El Ni o. In contrast, asee-saw mode is dominant during the EP El Ni o event with the maximum anomalyup to22cm in eastern tropical Pacific, and the minimum anomaly about-24cm in thewestern Warm Pool.The sea level varies with the evolution of El Ni o events, such as a rise–droppattern in the central equatorial Pacific while a drop–rise mode in the EOP during theCP El Ni o events. A persist rise (drop) pattern in the EOP (South PacificConvergence Zone), and a rise–drop pattern in the eastern equatorial Pacific duringEP El Ni o events.The discrepancy of the regional sea level variation has been effected by the different pattern of atmospheric wind field during the two types of El Ni o events, Itis found that in the central equatorial Pacific (EOP), the anomalous wind fieldsconverge (diverge), the thermocline deepens (shoals), the oceanic stratificationstrengthens (weakens), and the vertical mixing becomes tender (intensive), combiningwith the warm(cool) temperature anomaly in the subsurface and the positive (negative)heat content anomaly, which contribute to the sea level rising (falling) during the CPevents. While the wind fields converge (diverge) in the eastern equatorial Pacific(Warm Pool) which cause the sea level rising (falling) during the EP events.Interannual sea level variation has a relationship with the atmospheric wind fieldby local and remote processes in the EOP. The two effects have a striking discrepancybetween the two types of El Ni o events. The effect caused by the Rossby wave isdominant compared with the local Ekman pumping effect. Meanwhile the wind fieldeffects during the EP El Ni o are larger than that in the CP El Ni o events. The localwind contributes to sea level evolution primarily in the beginning of the El Ni oevents. The remote process of the Rossby wave persists in35%of the three CP ElNi o phases, while the predicted skill distribution, about43-53%, maps geographicalvariability in the EP El Ni o event.The simulations of the ROMS model show that the interannual sea levelvariation is effected by the atmospheric wind field remarkably and geographically.During the EP El Ni o event, the wind field impacts the sea level variationssignificantly, and its contribution is nearly40-60%. During the CP El Ni o, theatmospheric effect of wind field contributes remarkably during the developing andmature phases in the EOP.