Relative Effect of Indian Ocean in the Indo-Pacific/North America Teleconnection

The impact of the Indian Ocean on North America has long been considered a passive and secondary effect of the El Niño–Southern Oscillation (ENSO)-induced Pacific–North American (PNA) teleconnection, largely because of the strong covariability between the Pacific and Indian Ocean, as well as the small interannual variance of Indian Ocean sea surface temperatures (SSTs). However, the relative importance of the Indian Ocean–induced teleconnection has not been well quantified. In this study, with a combination of observation-based statistical analysis and atmospheric model simulations, we single out the Indian Ocean–North American (INA) teleconnection pattern, represented as a Rossby wave train pattern from the subtropical Indian Ocean to North America along the westerly jet. While the PNA pattern drives a north–south contrast temperature pattern over North America in boreal winter, the Indian Ocean warming in turn induces an eastern warming–western cooling pattern. Further analysis indicates that both the atmospheric circulation and surface temperature anomalies associated with the PNA and INA patterns are additive. More importantly, about half of the Indian Ocean SST variability is independent of ENSO, which also contributes substantially to the wintertime North American climate. During ENSO events, an anomalously warm or cold Indian Ocean may drive distinct climate anomalies over the east and west coasts of the United States. Our study highlights the relative importance of the Indian Ocean in driving the tropical ocean–midlatitude teleconnection patterns, which has broad implications for the predictability and future projection of wintertime North American climate.