Abstract
The fluctuation of the subsurface ocean heat condition along the equatorial Pacific is associated with the mass/heat exchanges between the equatorial and off-equatorial regions, which is the main cause of the phase transitions during the El Niño–Southern Oscillation (ENSO) cycle. In this work, the connection between the meridional transport convergences (MTCs) along the equatorial Pacific and variations of the warm water volume in the equatorial Pacific and their connections with the ENSO cycle are investigated. It is noted that the Sverdrup MTC induced by the wind stress curl has a significant impact on the thermocline fluctuation in nearly the entire equatorial Pacific but the impacts of its components vary with longitude. The component induced by the Ekman currents has a significant contribution from 150° W eastward to the coast, as well as the far-western Pacific, while the geostrophic component has a significant contribution in the central Pacific. There is a strong compensation between the surface wind stress-induced Ekman MTC and the Ekman pumping-induced geostrophic MTC which is confined in the central Pacific. Furthermore, the geostrophic component facilitates the phase transition of the ENSO cycle, while the Ekman component compensatively hinders it. The longitudinally varying component of the MTC enhances the anomalous thermocline tilting during the ENSO growth and maturing phases. These results may benefit the understanding, monitoring, and forecasting of ENSO evolution.
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Acknowledgements
The authors thank the reviewers for their constructive comments and insightful suggestions. GODAS and surface wind stress data from the National Environmental Prediction Center and Department of Energy reanalysis are available through Behringer (2007) and Li et al. (2020), and Kanamitsu et al. (2002), respectively. The data used in this study can be downloaded from https://www.esrl.noaa.gov/psd/data/gridded/data.godas.html and https://psl.noaa.gov/data/gridded/data.ncep.reanalysis2.html, or contact us via xiaofanli@zju.edu.cn. X. L. is supported by the National Natural Science Foundation of China (41930967). Z. H. is supported by the NOAA CTB project NA20OAR4590316. B. H. is supported by the NOAA MAPP drought project (NA17OAR4310144).
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Li, X., Hu, ZZ., Huang, B. et al. Oceanic meridional transports and their roles in warm water volume variability and ENSO in the tropical Pacific. Clim Dyn 59, 245–261 (2022). https://doi.org/10.1007/s00382-021-06124-w
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DOI: https://doi.org/10.1007/s00382-021-06124-w