Characteristics And Mechanism On Low Frequency Variations Of Sea Level In The Tropical Indian Ocean

Based on the satellite altimeter data, tide gauge data and sea level reconstructiondata systematically analyzed the tropical Indian Ocean sea level low frequency variationcharacteristics, mainly is the interannual features; Combining the relationship betweensea level variation and thermohaline, flow field and wind field, low frequency variationmechanism are discussed.The interannual variation of sea level in the tropical Indian Ocean has significantregional character, mainly concentrated in the southwest of the tropical Indian Oceanand coast of Sumatra-Java, standard deviation general up to8cm. The sea level EOFfirst mode variance contribution is44.3%, a reverse change; the second mode is mainlyfor "sandwich" structure. Southwest tropical Indian Ocean sea level variation lagSumatra-Java sea area for3months, the correlation coefficient up to-0.88, the timeseries of the8tide stations along Indian peninsula coast and the8tide stations alongwestern Australia have a very good lag correlation. The sea level variation when bothIOD and ENSO occurred is more significant than IOD occurred. The IOD event playsan important role on interannual sea level variations than ENSO event. The remarkablesea level variations associate with IOD event illustrates in the whole tropical basin,while the ENSO’s is mainly located in the southern tropical Indian Ocean. Australia’swestern coast sea level and ENSO index has good negative correlation relationship atthe same time, reach-0.6, the sea level of Fremantle tide gauge station in the west coastand ENSO index have a correlation coefficient is0.66.The decadal variation of the sealevel exist in the tropical Indian Ocean, in the southwest of the tropical Indian Oceanand Sumatra-Java sea area up to3cm. The sea level decadal variation has significantspatial difference, its spatial distribution are similar with interannual variation, has anegative relationship with the PDO (Pacific decadal oscillation). The reconstruction data EOF first mode variance contribution is73.3%, and showed a negative correlationwith the PDO index, the correlation coefficient is-0.48,1974and1994are at theextreme value of decadal; the correlation coefficient between the Australia tide gaugedata time series in the west coast and the PDO index reaches-0.75.The main influence factors of regional sea level interannual variations are stericeffect and atmospheric wind field force, ocean circulation and net heat flux play animportant role in the local area. The atmospheric wind field affects sea level interannualvariations by Ekman effect and baroclinic Rossby waves, which has significant regionalcharacteristics. The Rossby waves can explain more than30%of the sea level variationson ocean basin scale. Only in the Arabian Sea and the center area of the equatorialIndian Ocean, the local Ekman effect is more effective. The significant discrepancy ofthe interannual sea level variations is mainly caused by the different distribution of windfield.On the ocean basin scale, steric effect can explain at least50%of the sea levelvariations. The uplifting(sinking) of the main thermocline with the increasing(cooling)of the seawater temperature, sea level rise(sink), corresponding of seawater temperaturevertical structure change and sea level interannual variations have a good consistency.Most of the sea level variations in the tropical Indian Ocean caused by the sea surfacenet heat flux are negatively correlated with the observed sea level variations, but heatflux play an important role in the Arabian Sea. Composite analysis shows that in thesouthwest tropical Indian Ocean appear anticlockwise vortex flow, and the backgroundflow field is clockwise, the strongest during IOD+ENSO events, the second during IODevent and the weakest during ENSO events; The anticlockwise flow field inducepositive sea level variations in the southwest of the tropical Indian Ocean during threeevents, the transport of flow field has a very good adjustment effect on sea levelvariations. The existence of Indonesia through flow connects the sea level variations ofwestern Pacific with Australia’s west coast.