SAM-ENSO Index (SEI)

Note: This v.3 updates the SEI data up to the 01.10.2025 as new SAM and ENSO data became available. The SAM-ENSO climate index (SEI) provided here combines the Southern Anular Mode (SAM) index (Marshall, 2003) with the Oceanic Niño Index (ONI) (Bamston et al., 1997; Huang et al., 2016), taking into account that their opposing phases reinforce each other in their overlapping effects on the wind field around Antarctica (Fogt et al., 2011; McKee et al., 2011; Stammerjohn et al., 2008). \(SEI = {SAM \over std(SAM)} - {ONI \over std(ONI)}\) The SEI has been first employed in Llanillo et al. (2023). References: Bamston, A. G., Chelliah, M., & Goldenberg, S. B. (1997). Documentation of a highly enso-related sst region in the equatorial pacific: Research note. Atmosphere - Ocean, 35(3), 367–383. https://doi.org/10.1080/07055900.1997.9649597 Fogt, R. L., Bromwich, D. H., & Hines, K. M. (2011). Understanding the SAM influence on the South Pacific ENSO teleconnection. Climate Dynamics, 36(7), 1555–1576. https://doi.org/10.1007/s00382-010-0905-0 Huang, B., Thorne, P. W., Smith, T. M., Liu, W., Lawrimore, J., Banzon, V. F., Zhang, H. M., Peterson, T. C., & Menne, M. (2016). Further exploring and quantifying uncertainties for extended reconstructed sea surface temperature (ERSST) version 4 (v4). Journal of Climate, 29(9), 3119–3142. https://doi.org/10.1175/JCLI-D-15-0430.1 Llanillo, P.J., Kanzow, T., Janout, M. and Rohardt, G. (2023): The Deep-Water Plume in the northwestern Weddell Sea, Antarctica: Mean state, seasonal cycle and interannual variability influenced by climate modes. Journal of Geophysical Research Oceans, 128(2), https://doi.org/10.1029/2022JC019375 Marshall, G. J. (2003). Trends in the Southern Annular Mode from observations and reanalyses. Journal of Climate, 16(24), 4134–4143. https://doi.org/10.1175/1520-0442(2003)016<4134:TITSAM>2.0.CO;2 McKee, D. C., Yuan, X., Gordon, A. L., Huber, B. A., & Dong, Z. (2011). Climate impact on interannual variability of Weddell Sea Bottom Water. Journal of Geophysical Research: Oceans, 116(5), 1–17. https://doi.org/10.1029/2010JC006484 Stammerjohn, S. E., Martinson, D. G., Smith, R. C., Yuan, X., & Rind, D. (2008). Trends in Antarctic annual sea ice retreat and advance and their relation to El Niño–Southern Oscillation and Southern Annular Mode variability. Journal of Geophysical Research, 113(C3), C03S90. https://doi.org/10.1029/2007JC004269