# Machine Learning Reconstruction of Wyrtki Jet Seasonal Variability in the Equatorial Indian Ocean
## 1 Introduction  
The Wyrtki Jet (WJ), a strong eastward equatorial current in the Indian Ocean directly driven by equatorial westerly winds [1], constitutes a critical component of the Indian Ocean circulation system. The WJ regulates the zonal transport of water masses, salinity, and heat in the upper ocean between the tropical eastern and western Indian Ocean, while influencing basin-scale air-sea interactions [2, 3, 4, 5, 6]. The WJ exhibits pronounced seasonal variability, forming during monsoon transition periods and intensifying with narrow flow widths in boreal spring (April-May) and autumn (October-November) [1]. Both theoretical calculations and observational data indicate that the autumn WJ exhibits consistently higher current velocities (70-100 cm/s) compared to spring (50-90 cm/s). This conclusionis supported by multiple methodologies, including direct buoy measurements [7], drifting buoy trajectories, and satellite altimeter datasets [8], collectively demonstrating the consistency and reliability of the research findings. However, [PERSON] et al. [9] identified anomalous behavior in the 2013 spring WJ within the eastern equatorial Indian Ocean, where spring velocities slightly exceeded autumn values. Additionally, these studies have not only validated the fundamental seasonal variability characteristics of the WJ but have further quantified its intensity differences. Such advancements hold significant implications for elucidating the seasonal adjustment mechanisms of the Indian Ocean circulation system. Figure 1 illustrates the 30-year (1993-2022) seasonal mean zonal velocity distribution of the WJ in the equatorial Indian Ocean. The data reveal that the zonal velocity reaches 0.3 m/s in spring, gradually dissipates in summer, peaks at 0.5 m/s in autumn (significantly exceeding spring values), and disappears in winter. These findings align with previous studies [1; 7; 8], further corroborating the pronounced seasonal variability of the WJ. During summer and winter, the jet weakens substantially, with winter exhibiting a distinct westward flow. During WJ events, surface currents in the central equatorial Indian Ocean can exceed 80 cm/s [10]. The resultant large-scale water mass transport drives eastward advection of warm surface waters from the central equatorial Indian Ocean, redistributing heat and salt across the central and eastern equatorial Indian Ocean [11; 12; 13]. This process elevates (depresses) sea surface height (SSH) in the eastern (western) equatorial Indian Ocean, deepens (shoals) the thermocline [14; 15], and consequently modulates sea surface temperature variability in the eastern Indian Ocean Warm Pool and upwelling activity [16]. Therefore, accurate reconstruction of the WJ in the equatorial Indian Ocean is critical for elucidating its role in basin-scale water exchange and energy cycling within the Indian Ocean system. In oceanographic research, the acquisition of sea surface current data remains a critical challenge. This issue is particularly pronounced in regions, such as the equatorial Indian Ocean, where observational data for surface current fields, like the Wyrtki Jet, are extremely scarce. Currently, surface ocean current datasets primarily originate from three sources: first, direct observations through oceanic drifting buoys. For instance, the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) project deployed a mooring-mounted Acoustic Doppler Current Profiler (ADCP) at 0\({}^{\circ}\), 80.5\({}^{\circ}\) E in the central equatorial Indian Ocean in August 2008, conducting current observations in the upper ocean layer above 200 m [17]. However, this method suffers from long-term data gaps and discontinuity issues, primarily due to instrument malfunctions or deployment failures. Second, current calculations have been derived from satellite remote sensing data.