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Bimodal Astroclimatic Modulation of ENSO Dynamics by Net Shortwave Solar Radiation
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Abstract
The persistent Spring Predictability Barrier (SPB) suggests that current ENSO models may omit a crucial external forcing. This study identifies and quantifies a bimodal, season-dependent modulation of the El Niño–Southern Oscillation (ENSO) during the 1999–2024 period, driven by variations in net short-wave solar radiation. Using a SARIMAX framework combined with permutation tests, two distinct regimes were identified: a Short Cycle (March–May) showing a significant positive association with the Oceanic Niño Index (ONI), and a Long Cycle (June–February) exhibiting an inverse relationship. These empirical patterns demonstrate that the ENSO system responds differentially to solar radiation depending on the seasonal phase, providing a new astroclimatic perspective on its dynamics. The methodology rigorously accounts for intrinsic red noise and internal ONI autocorrelations, establishing a physically coherent mechanism that links seasonal orbital forcing to the ENSO energy balance. By integrating the SPB within an empirical external-forcing framework, these findings offer new insights that may enhance seasonal-to-annual predictability and improve the physical realism of ENSO models.
DOI
https://doi.org/10.31223/X50Q92
Subjects
Physical Sciences and Mathematics
Keywords
Interannual Climate Variability, El Niño–Southern Oscillation (ENSO), Astroclimatology, Bimodal Forcing, Solar Radiation, Seasonal Modulation, numerical models
Dates
Published: 2025-10-27 22:51
Last Updated: 2025-10-27 22:51
License
CC BY Attribution 4.0 International
Additional Metadata
Conflict of interest statement:
None
Data Availability (Reason not available):
Data Availability Oceanic Niño Index (ONI) data for seasons were obtained from the NOAA Climate Prediction Center (2024), available at: https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php Astronomical ephemerides, including Earth–Sun distance and solar declination, were calculated using the IMCCE Solar System ephemeris service via its Solar System Portal: (Orbital Ephemerides) : https://ssp.imcce.fr/forms/ephemeris Dates of solstices and equinoxes were sourced from NASA’s ModelE AR5 Simulations dataset provided by the Goddard Institute for Space Studies (GISS): https://data.giss.nasa.gov/modelE/ar5plots/srvernal.html Net downward shortwave radiation data were obtained from NASA’s MERRA-2 reanalysis via the Goddard Earth Sciences Data and Information Services Center (GES DISC), using the open water net downward shortwave flux product for marine regions: https://giovanni.gsfc.nasa.gov/giovanni For further information on measurement definitions, see: https://disc.gsfc.nasa.gov/information/glossary?title=Giovanni%20Measurement%20Definitions:%20Net%20Radiation All datasets used in this study are openly accessible and were utilized in accordance with their respective data use policies. All graphics were generated by the author using publicly available datasets; no copyrighted or third-party material was reproduced.
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