Characterizing ENSO coupled variability and its impact on North American seasonal precipitation and temperature

Here, we re-examine whether ENSO can be adequately characterized by a simple, seasonally invariant time series, such as the Niņo-3.4 SST index, or whether the addition of outgoing long wave radiation (OLR) is needed to adequately represent the coupled system. We also explore whether the use of a combined index of SST with OLR explains additional variance of North American temperature and precipitation anomalies beyond those described by using a single index alone.

As a first step, we define ENSO as the leading mode of seasonally varying canonical correlation analysis (CCA) between anomalies of tropical Pacific SST and OLR. The CCA reveals that the strongest regions of coupling are mostly invariant as a function of season and correspond to an OLR region located in the Central Pacific Ocean and an SST region in the east Pacific that coincides with the Niņo-3 region.

With ENSO defined using area-averages over these regions, we then examine whether indices of a single component, SST or OLR, or the combination help to quantify U.S. climate impacts. We find that a combined index describes more variability in winter/spring precipitation and summer temperature over certain regions.