Low Frequency Change Of Sea Level Anomalies In The Bay Of Bengal And Its Response To ENSO

The low frequency change of sea level anomalies (SLA) in the Bay of Bengal isinvestigated based on the merged altimeter data from AVISO/CNES ranged fromJanuary1993to December2009．Detailed analysis shows that the sea level variabilityis closely related to ENSO. When an El Ni o event took place such as in l997, the sealevel of the Bay of Bengal showd a negative anomaly．While in a La Ni a event suchas in1998, a reverse situation took place．The EOF analysis shows that the mainmode of the low frequency change of SLA in Bay of Bengal can be called as anENSO mode, with its variance contribution33%. The EOF1stmode time series has acorrelation coefficient of-0.64with Nino3/SST index. In combination with the spacialdistribution, EoF1stmode shows that in El Ni o year, coastal SLA decreases andcentral SLA rises. In La Ni a year, the opposite situation takes place.A CSVD (Complex Singular Value Decomposition) analysis is completed usingSLA and CCMP (Cross-Calibrated Multi-Platform Ocean Surface Wind Components)local wind data. CSVD1stmode SLA time series has a correlation coefficient of0.73with wind time series. The correlation coefficient of SLA time series and wind timeseries with Nino3index is0.62and0.53respectively. Another CSVD analysis is doneusing SLA and NCEP/NCAR850hPa wind data over tropical Indian Ocean andPacific Ocean. SLA time series of CSVD1stmode, whose covariance contribution of75.54%, has a correlation coefficient of0.72with wind time series. The respectivecorrelation coefficient of SLA time series and wind time series with Nino3index is0.64and0.78. So we obtain the conclusion that ENSO mode is the main mode ofinterannual change of SLA in Bay of Bengal and wind anomaly over tropical Indianand Pacific Ocean. Wind anomaly over the equatorial east Indian Ocean can exciteKelvin waves which can become coastal Kelvin waves and reach the east and northboundary of Bay of Bengal. Together with the anticyclonic wind stress anomaly it caninfluence sea level change of the Bay of Bengal. During El Ni o years, there is ananticyclone over the Bay of Bengal, causing an Ekman transport to pile up water inthe centre, at the same time reduce the water around coastal area in the Bay of Bengal.Steric sea level anomaly is the main reason for the low frequency change of the SeaLevel Anomaly. Through wavelet coherence analysis, it’s found that the steric sealevel anomaly has a good coherence with Nino3/SST index on3.5-5year periods. Theopposite phase indicates that when El Ni o event took place, SST over East TropicalPacific increases and the mean steric sea level in Bay of Bengal decreases. Being apart of the West Pacific-East Indian Ocean warm pool, the sea water temperature inthe Bay of Bengal cools when an El Ni o took place, causing the steric sea level todecrease.