Energy Studies On The Eddy-mean Flow Interactions In The Bay Of Bengal

Oceanic reanalysis data produced by Simple Ocean Data Assimilation(SODA)and the wind field data produced by NCEP(National Center for Environmental Prediction)are used in this paper to synthesize and analyze the onset date of Southwest Indian Ocean monsoon and the abnormal development of wind field from 2000 to 2016 under the influence of El Nino/La Nina events.energy analysis method used to diagnose the interannual variability of eddy-mean flow interaction in the Bay of Bengal(BOB)during summer and autumn from 2000 to 2015.Southwest monsoon over the Indian Ocean breaks out and prevails in summer and autumn.As a strong climatic anomaly signal,the development of El Nino/La Nina event could change the atmospheric circulation over the Indian Ocean.In this paper,we analysed the correlation between the onset date of the southwest monsoon and the ocean Nino index(ONI)in order to find out the correlation between the onset date of the southwest monsoon and the El Nino/La Nina event.By synthesizing wind speed data over 1000 hpa and 850 hpa isobaric surfaces,we discussed the anomalies of wind speed and direction before and after the onset of southwest monsoon under the influence of El Nino and La Nina events respectively.The results indicating that the development of the El Nino event will delay the onset of the southwest monsoon,and the wind field over the Bay of Bengal has not increased significantly.On the contrary,the impact brought by the La Nina event is opposite,the onset date of the monsoon is advanced and the strength of wind field over the Bay of Bengal is enhanced significantly.The gradient of the equatorial Indian Ocean zonal sea surface temperature anomaly developed by the Indian Ocean Dipole event will also drive the anomalous variation of the Indian Ocean atmospheric circulation.We synthesized and compared the effects on the wind field over the Bay of Bengal that modulated by different IOD events.The results reveals that the southwesterly wind over the Bay of Bengal is strengthened in the negative IOD anomaly year and has a weak cyclonic circulation anomaly.The high values of EKE(Eddy Kinetic Energy)in the Bay of Bengal are mainly centered at the northern part of the bay's western boundary and the eastern and western sides of the Bay mouth.The results show that the eddy-mean flow interaction in the Bay of Bengal is stronger in negative IOD anomaly year than in positive IOD anomaly year.The analysis illustrates that the wind field over the Bay of Bengal is stronger in the negative IOD anomaly year,The current velocity shear and the instability process in the upper ocean increased,therefore,the interaction between eddies and mean-flow is enhanced,more ocean energy is transferred from the mean flow field to the eddy field.In addition,we found that EKE around Bay mouth area is tend to develop a significant anomaly in negative IOD anomaly year compare to climatic spatial distribution pattern,so we chose typical negative IOD year 2010 as an example for more detailed analyses.Further study on budget of Bay mouth EKE anomalous area demonstrates that the main influencing factors of EKE interannual variation is the work done by the pressure term,the work done by barotropic instability process and advection term are weak when compared to pressure term,the contribution of the work done by the surface wind stress is low.