Seasonal Rainfall Predictions From Sea Surface Salinity Anomalies

We have discovered that sea surface salinity (SSS) is a better seasonal predictor of terrestrial rainfall than sea surface temperature (SST) or the usual pressure modes of atmospheric variability.  In many regions, a 3-6 month lead of SSS over rainfall on land can be seen.  While some lead is guaranteed due to the simple conservation of water and salt, the robust seasonal lead for SSS in some places is truly remarkable, often besting traditional SST and pressure predictors by a very significant margin.  One mechanism for the lead has been identified in the recycling of water on land through soil moisture in regional ocean to land moisture transfers (Li et al, 2016a, __, 2016b).  However, a global search has yielded surprising long-range SSS-rainfall teleconnections for other areas.  It is suggested that these teleconnections indicate a marked sensitivity of the atmosphere to where rain falls on the ocean.  That is, the latent heat of evaporation is by far the largest energy transfer from ocean to atmosphere and where the atmosphere cashes in this energy in the form of precipitation is well recorded in SSS.  SSS also responds to wind driven advection and mixing.  Thus, SSS appears to be a robust indicator of atmospheric energetics and moisture transport and the timing and location of rainfall events is suggested to influence the subsequent evolution of the atmospheric circulation. In a sense, if the fall of a rain drop is at least equivalent to the flap of a butterfly’s wings, the influence of a billion butterfly rainstorm allows for systematic predictions beyond the chaotic nature of the turbulent atmosphere.  SSS is found to be particularly effective in predicting extreme precipitation or droughts, which makes its continued monitoring very important for building societal resilience against natural disasters.

References:

Li, L., R. W. Schmitt, C. C. Ummenhofer, and K. B. Karnauskas, 2016a.  North Atlantic salinity as a predictor of Sahel rainfall. Science Advances, 2, e1501588.

Li, L., R. W. Schmitt, C. C. Ummenhofer, and K. B. Karnauskas, 2016b.  Implications of North Atlantic sea surface salinity for summer precipitation over the US Midwest: Mechanisms and predictive values. J. Climate, 29, 3143-3159.