A second-generation global internal tide model from satellite altimetry

Internal tides are ubiquitous in the global ocean and play an important role in various ocean processes. It is a challenging and rewarding task to construct internal tide models for the oceanographic community. Satellite altimetry is fortunately the only practical technique for observing internal tides on a global scale. However, there are a number of issues in extracting the much weaker internal tide signal out of nontidal noise O (10) times larger. These difficulties are mainly caused by (1) the relatively low spatiotemporal sampling rate with conventional nadir-looking satellite altimetry and (2) the complex nature of the multiconstituent multimodal multidirectional internal tide field. Based on the success of our first-generation global internal tide model, in this project, we have constructed a second-generation model by addressing two key issues: (1) west-east propagating internal tides previously missed can be retrieved by a newly-developed mapping technique; (2) seasonal and interannual variations of internal tides are determined and taken into account. The new model is evaluated using independent satellite data from altimeter missions Cryosat-2, Haiyang-2A, Setinal-3, and ALtiKa. Significant improvements are demonstrated. Meanwhile, we identify some issues (e.g., multiple baroclinic modes) that can and will be addressed for constructing next-generation internal tide models.