Enhanced North American ENSO Teleconnections During the Little Ice Age Revealed by Paleoclimate Data Assimilation

Abstract

AbstractTeleconnection rainfall over North America may be systematically altered by tropical Pacific mean state changes. Characterizing teleconnection changes to improve prediction requires many realizations of ENSO events, but twentieth century data are temporally limited. To extend twentieth century records, we evaluate ENSO events in a new last‐millennium paleoclimate data assimilation reconstruction to deduce how mean state changes affect the magnitude/extent of ENSO‐driven rainfall in the United States. Despite global cooling during the Little Ice Age, the central‐eastern tropical Pacific warms relative to the Medieval Climate Anomaly, shifting teleconnections eastward and increasing rainfall anomalies in the southwestern United States. Teleconnections strengthen independently of ENSO amplitude; we thus suggest caution in using paleoclimate reconstructions of teleconnection rainfall as a proxy for ENSO amplitude. We demonstrate teleconnection rainfall is sensitive to the pattern of tropical Pacific mean SST changes, underscoring the importance of reducing uncertainties in future warming patterns in the tropical Pacific.