Study On Seasonal Variation Of Upper Layer Circulation And Its Mechanism In Lombok Strait And Adjacent Sea Area

Based on the MITgcm model,a high-resolution numerical experiment was conducted to simulate the circulation of the Indonesian sea from January to June2002.The analysis results show that MITgcm can simulate the circulation of the Indonesian area,and describe the shape of the Indonesian throughflow(ITF)in detail.The transports of Lombok,Ombai and Makassar straits are basically consistent with the observation data.From the perspective of MITgcm model,the circulation structure of Lombok sea area is influenced by the Makassar strait throughflow and Karimata strait throughflow.We found that in the first three months,the Lombok strait was mainly affected by the joint action of two throughflows.From April to June,with the local monsoon turning,KSTF turn to the east,and MSTF become the main factor affecting the Lombok strait.This conclusion is supported by the thermohaline variation of MITgcm model.Based on Ocean Forecast Australian Model data,we investigated seasonal variation characteristics of the upper layer circulation of Lombok sea area and what is its influencing factors by using multiple statistical methods such as spectral analysis and composite analysis.The results indicated that the average volume transport of Lombok strait accounts for 15% of that of Indonesian throughflow,which shows distinctive seasonal variation feature—strong in winter and weak in summer in the southern hemisphere.Half a year and one year are its typical cycle.Owing to the cyclical effect of Karimata strait throughflow with high temperature and low salt water mass and Makassar strait throughflow with low temperature and high salt water mass,significant seasonal structural differences exist in the upper circulation of the Lombok sea area.There is a difference between the results of MITgcm and OFAM,the evolution of circulation structure in MITgcm is one month in advance.Further analyses suggest that local wind,submarine topography and MJO are the main influencing factors of the seasonal variation of the upper circulation structure in the Lombok sea area.