Impacts of canonical and Modoki El Nino on tropical Atlantic SST

The impacts of canonical and Modoki El Nino on tropical Atlantic sea surface temperature (SST) are quantified using composite analysis. Results show that El Nino Modoki fails to produce significant warming in the tropical Atlantic, in contrast to the well known warming following canonical El Nino events. El Nino Modoki instead induces significant cooling in the northeastern tropical Atlantic and near-neutral conditions elsewhere in the tropical Atlantic. It is shown that the difference in SST response stems primarily from a much stronger Pacific/North American (PNA) teleconnection pattern and stronger atmospheric Kelvin wave response during canonical events compared to Modoki. The stronger PNA pattern and Kelvin waves during canonical events generate anomalously weak surface winds in the tropical North Atlantic, driving anomalously weak evaporative cooling and warmer SSTs. Past research has shown significant decadal variability in the frequency of noncanonical El Ninos relative to canonical events. If such variability continues, it is likely that the impact of El Nino on tropical Atlantic SST will also fluctuate from one decade to the next.